1 Technical Overview {#technical_overview}
2 ========================================
6 @section OCCT_TOVW_SECTION_1 Product Overview
8 Open CASCADE Technology is an object-oriented C++ class library designed for rapid production of sophisticated domain-specific design applications. A typical application developed using OCCT deals with two or three-dimensional (2D or 3D) geometric modeling
9 in general-purpose or specialized Computer Aided Design (CAD) systems, manufacturing
10 or analysis applications, simulation applications, or illustration tools. OCCT Object
11 Libraries help you to develop your applications significantly faster.
13 @image html /technical_overview/images/technical_overview_over.png
14 @image latex /technical_overview/images/technical_overview_over.png
16 The OCCT Library provides the following services:
19 * 2D and 3D geometric modeling toolkits which allow you to model any type of object:
20 * Creating primitives such as prism, cylinder, cone and torus
21 * Performing Boolean operations (addition, subtraction and intersection)
22 * Tweaking constructions using fillets, chamfers and drafts
23 * Modeling constructions using offsets, shelling, hollowing and sweeps
24 * Computing properties such as surface, volume, center of gravity, curvature
25 * Computing geometry using projection, interpolation, approximation
26 * Visualization services that allow you to manage object display and manipulate views, for example:
30 * The application framework features:
31 * Association between non-geometric application data and geometry
32 * Parameterization of models
33 * Java Application Desktop (JAD), a framework for creating your Graphical User Interfaces (GUI)
34 * Data exchange providing import and export functions of OCCT models to and from standard formats such as IGES and STEP
36 OCCT Library is developed and marketed by OPEN CASCADE Company. The library is designed
37 to be truly modular and extensible. As such, they separate C++ classes for:
39 * Defining data structures (geometric modeling, display and graphic selection)
40 * Implementing complex algorithms
41 * Providing Application Programming Interfaces (APIs)
44 Related classes are grouped into packages to prevent any class-name conflicts;
45 C++ class-names are prefixed by a package name. For example, all classes defining
46 3D geometric objects belong to the Geompackage.
47 In Geom, the class implementing Bezier surfaces is called BezierSurface, and its full name is <i> Geom_BezierSurface</i>.
49 Packages are then archived into libraries, to which you can link your application.
51 Finally, libraries are grouped into six modules: Foundation Classes,
52 Modeling Data, Modeling Algorithms, Visualization, Data Exchange and Application Framework.
54 In addition Draw Test Harness (Draw) provides testing tools for the Visualization,
55 Modeling Algorithms, Application Framework and Data Exchange modules.
56 These tools include a wide range of interpreted commands which allow experimenting with OCCT.
58 Refer to the Technical Overview and OCCT documentation for details about the services provided in each module.
60 @section OCCT_TOVW_SECTION_2 Foundation Classes
63 Foundation Classes provide a variety of general-purpose services such as:
65 * Primitive types, strings and various types of quantities
66 * Automated management of heap memory
68 * Classes for manipulating data collections
69 * Math tools such as vectors, matrices and primitive geometric types
70 * Basic services for saving data in ASCII files
72 These services are organized into the following libraries:
78 The technical overview provides only a basic description of the libraries. Please, refer for more details to Foundation Classes User's guide
80 See also: our web site at E-learning and Training.
82 @subsection OCCT_TOVW_SECTION_2_1 Kernel Classes
88 Root Classes, primarily implemented in the Standard package, are the predefined classes on which
89 all other Open CASCADE Technology classes are built. They provide:
91 * Primitive types such as Boolean, Character, Integer or Real
92 * Memory manager based on reference counting for optimizing the allocation and deallocation of large numbers of small C++ objects
93 * <i>Standard_Transient</i> class automating memory management through smart pointers
94 * OCCT <i>Handle</i>; most of OCCT classes inherit from this base class.
95 * Management of exceptions,
96 * Encapsulation of C++ streams.
100 Quantity classes provide the following services:
102 * Definition of primitive types representing most of mathematical and physical quantities
103 * Unit conversion tools.
104 * Resources to manage time information such as dates and time periods
105 * Resources to manage color definition
107 A mathematical quantity is characterized by the name and the value (real).
108 A physical quantity is characterized by the name, the value (real) and the unit.
109 The unit may be either an international unit complying with the International Unit System (SI)
110 or a user defined unit. The unit is managed by the physical quantity user.
112 The fact that both physical and mathematical quantities are manipulated as real
115 * They are defined as aliases of real values, so all functions provided by the <i>Standard_Real</i> class are available on each quantity.
116 * It is possible to mix several physical quantities in a mathematical or physical formula involving real values.
118 <i>Quantity</i> package includes all commonly used basic physical quantities.
122 Exception classes list all the exceptions, which can be raised by any OCCT function.
124 Each exception inherits from Standard_Failure either directly or by inheriting from
127 Exceptions describe anomalies which can occur during the execution of a method. With
128 the raising of an exception, the normal course of program execution is abandoned.
129 The execution of actions in response to this situation is called the treatment of
133 The methods try & catch are redefined in OCCT to work properly on any platform. Nevertheless
134 they call native mechanisms each time it is possible. The only reason not to use
135 native exceptions is that they may not work properly on some compilers. In this case,
136 a specific OCCT code is used instead.
141 Strings are classes that handle dynamically sized sequences of characters based on
142 ASCII/Unicode UTF-8 (normal 8-bit character type)
143 and UTF-16/UCS-2 (16-bit character type). They provide editing operations with built-in
144 memory management which make the relative objects easier to use than ordinary character
147 String classes provide the following services to manipulate character strings:
148 * Editing operations on string objects, using a built-in string manager
149 * Handling of dynamically-sized sequences of characters
150 * Conversion from/to ASCII and UTF-8 strings.
152 Strings may also be manipulated by handles and therefore, can be shared.
154 These classes are implemented in <i>TCollection</i> and <i>NCollection</i> packages.
159 Apart from strings, the <i> TCollection</i> package contains classes of dynamically sized
160 aggregates of data. They include a wide range of collections.
162 * Arrays (unidimensional and bidimensional) are generally used for quick access to an item.
163 Note that an array is a fixed-sized aggregate.
164 * Sequences are ordered collections of non-unique objects.
165 A sequence item is longer to access than an array item: only an exploration in sequence
166 is efficient (but sequences are not adapted for numerous explorations).
167 Arrays and sequences are commonly used as data structures for more complex objects.
168 * Maps are dynamic structures where the size is constantly adapted to the number of inserted
169 items and access to an item is the fastest. Maps structures are commonly used in
170 cases of numerous explorations: they are typically internal data structures for complex
171 algorithms. Sets generate the same results as maps but computation time is considerable.
172 * Lists, queues and stacks, which are minor structures similar to sequences but with different
173 algorithms to explore them
174 * Specific iterators for sequences, maps, and stacks.
176 Most collections follow value semantics: their instances are the actual collections,
177 not handles to a collection. Only arrays, sequences and sets may also be manipulated
178 by handle, and therefore shared.
181 Collection classes are generic (C++ template-like), so they can contain
182 a variety of objects which do not necessarily inherit from
183 a unique root class. When you need to use a collection of a given object type, you
184 must instantiate the collection for this specific type. Once the code for this declaration
185 is compiled, all functions available on the generic collection are available on your
188 Each collection directly used as an argument in Open CASCADE Technology public syntax
189 is instantiated in an OCCT component using the corresponding generic class in package
190 <i> TCollection</i>, by means of compiling the CDL declaration of the instance.
191 Thus OCCT generic classes require compilation of definitions in the CDL language and therefore
192 can only be instantiated in WOK.
194 If you are not using CDL in your project (CDL compilation under WOK is necessary
195 to instantiate any generic Collection from package <i>TCollection</i>), then you should
196 use the Collections defined in <i> NCollection</i> package. It contains definitions of the
197 same generic collection classes described above, but in a form of C++ templates.
198 Therefore, to instantiate any collection type no additional support is required beyond
199 the ANSI C++ compiler.
201 @subsection OCCT_TOVW_SECTION_2_2 Math Utilities
204 ### Vectors and Matrices
207 The <i> Vector</i> and <i> Matrix </i> classes provide commonly used mathematical algorithms which
210 * Basic calculations involving vectors and matrices;
211 * Computation of eigenvalues and eigenvectors of a square matrix;
212 * Solvers for a set of linear algebraic equations;
213 * Algorithms to find the roots of a set of non-linear equations;
214 * Algorithms to find the minimum function of one or more independent variables.
216 These classes also provide a data structure to represent any expression,
217 relation, or function used in mathematics, including the assignment of variables.
219 Vectors and matrices have arbitrary ranges which must be defined at declaration time
220 and cannot be changed after declaration.
224 // a vector of dimension 3 with range (1..3)
226 math_Matrix m(0, 2, 0, 2);
227 // a matrix of dimension 3x3 with range (0..2, 0..2)
229 math_Vector v(N1, N2);
230 // a vector of dimension N2-N1+1 with range (N1..N2)
233 Vector and Matrix objects follow "value semantics", that is, they cannot be shared
234 and are copied though assignment.
237 math_Vector v1(1, 3), v2(0, 2);
239 v2 = v1; // v1 is copied into v2
240 // a modification of v1 does not affect v2
243 Vector and Matrix elements can be retrieved using indexes, which must be in the range
244 defined upon Vector/Matrix creation. The elements can be initialized with some numerical
245 value upon creation as well.
249 math_Matrix m(1, 3, 1, 3);
258 Some operations on Vector and Matrix objects may not be legal. In this case an exception
259 is raised. Two standard exceptions are used:
260 *<i>Standard_DimensionError</i> exception is raised when two matrices or vectors involved
261 in an operation are of incompatible dimensions.
262 *<i>Standard_RangeError</i>exception is raised if an attempt to access outside the range
263 defined upon creation of a vector or a matrix is made.
266 math_Vector v1(1, 3), v2(1, 2), v3(0, 2);
268 v1 = v2; // error: Standard_DimensionError is raised
269 v1 = v3; // OK: ranges are not equal, but dimensions are compatible
270 v1(0) = 2.0; // error: Standard_RangeError is raised
274 ### Fundamental Geometry Types
276 The Fundamental Geometry Types component groups the following packages:
277 * geometric processor package <i> gp</i>;
278 * <i>GeomAbs</i> package, which provides enumerations generally used in geometry;
280 <i>gp</i> package is a STEP-compliant implementation of basic geometric and algebraic
281 entities, used to define and manipulate elementary data structures.
283 In particular, <i>gp</i> provides:
285 * descriptions of primitive geometric shapes, such as:
289 * Circles and conics;
290 * Planes and elementary surfaces;
291 * positioning of these shapes in space or in a plane by means of an axis or a coordinate system;
292 * definition and application of geometric transformations to these shapes:
296 * Scaling transformations;
297 * Composed transformations;
298 * Tools (coordinates and matrices) for algebraic computation.
300 These functions are defined in 3D space and in the plane.
302 <i> gp</i> curves and surfaces are analytic: there is no parameterization and no orientation
303 on <i>gp</i> entities, i.e. these entities do not provide functions which work with these properties.
304 If you need, you may use more evolved data structures provided by <i> Geom</i>
305 (in 3D space) and <i> Geom2d</i> (in the plane). However, the definition of <i> gp</i> entities
306 is identical to the one of equivalent <i> Geom</i> and <i> Geom2d</i> entities, and they are located
307 in the plane or in space with the same kind of positioning systems.
308 They implicitly contain the orientation, which they express
309 on the <i> Geom </i> and <i> Geom2d </i> entities, and they induce the definition of their parameterization.
312 Therefore, it is easy to give an implicit parameterization to <i> gp</i> curves and surfaces,
313 which is the parametarization of the equivalent <i> Geom</i> or <i> Geom2d</i> entity. This property
314 is particularly useful when computing projections or intersections, or for operations
315 involving complex algorithms where it is particularly important to manipulate the
316 simplest data structures, i.e. those of <i> gp</i>. Thus, the <i> ElCLib</i> and <i> ElSLib</i> packages
317 provide functions to compute:
319 * the point of parameter u on a 2D or 3D gp curve,
320 * the point of parameter (u,v) on a gp elementary surface, and
321 * any derivative vector at this point.
323 Note: the <i> gp</i> entities cannot be shared when they are inside more complex data structures.
326 ### Common Mathematical Algorithms
328 Common mathematical algorithms provided in OCCT include:
330 * Algorithms to solve a set of linear algebraic equations,
331 * Algorithms to find the minimum of a function of one or more independent variables,
332 * Algorithms to find roots of one or of a set of non-linear equations,
333 * An algorithm to find the eigenvalues and eigenvectors of a square matrix.
335 @section OCCT_TOVW_SECTION_3 Modeling Data
337 Modeling Data supplies data structures to represent 2D and 3D geometric models.
339 @image html /technical_overview/images/technical_overview_md.png
340 @image latex /technical_overview/images/technical_overview_md.png
342 These services are organized into the following libraries:
349 The technical overview provides only a basic description of the libraries. Please,
350 refer for more details to Modeling Data User's guide
352 3D geometric models are stored in OCCT native BREP format. It is possible to learn
353 more about it in BREP Format Description White Paper
355 See also: our web site at E-learning and Training.
357 @subsection OCCT_TOVW_SECTION_3_1 2D Geometry Types
359 <i> Geom2d</i> package provides an implementation of 2D geometric objects complying with
360 STEP, part 42. In particular, it provides functions for:
361 * description of points, vectors and curves,
362 * their positioning in the plane using coordinate systems,
363 * their geometric transformation, by applying translations, rotations, symmetries, scaling transformations and combinations thereof.
365 The key characteristic of <i> Geom2d </i> curves is that they are parameterized.
366 Each class provides functions to work with the parametric equation of the curve,
367 and, in particular, to compute the point of parameter u on a curve and the derivative vectors of order 1, 2.., N at this point.
369 As a consequence of the parameterization, a <i> Geom2d </i> curve is naturally oriented.
371 Parameterization and orientation differentiate elementary <i>Geom2d </i>curves from their
372 equivalent as provided by <i> gp</i> package. <i> Geom2d</i> package provides conversion
373 functions to transform a <i> Geom2d</i> object into a <i> gp</i> object, and vice-versa, when this is possible.
375 Moreover, <i> Geom2d</i> package provides more complex curves, including Bezier curves,
376 BSpline curves, trimmed curves and offset curves.
378 <i> Geom2d </i> objects are organized according to an inheritance structure over several levels.
379 Thus, an ellipse (specific class <i> Geom2d_Ellipse</i>) is also a conical curve and inherits
380 from the abstract class <i> Geom2d_Conic</i>, while a Bezier curve (concrete class <i> Geom2d_BezierCurve</i>)
381 is also a bounded curve and inherits from the abstract class <i> Geom2d_BoundedCurve</i>;
382 both these examples are also curves (abstract class <i>Geom2d_Curve</i>). Curves, points
383 and vectors inherit from the abstract class <i> Geom2d_Geometry,</i> which describes the properties
384 common to any geometric object from the <i>Geom2d</i> package.
386 This inheritance structure is open and it is possible to describe new objects which
387 inherit from those provided in the <i>Geom2d</i> package, provided that they respect the
388 behavior of the classes from which they are to inherit.
390 Finally, <i> Geom2d</i> objects can be shared within more complex data structures.
391 This is why they are used within topological data structures, for example.
393 <i> Geom2d </i>package uses the services of the <i> gp</i> package to:
395 * implement elementary algebraic calculus and basic analytic geometry,
396 * describe geometric transformations which can be applied to <i> Geom2d</i> objects,
397 * describe the elementary data structures of <i>Geom2d</i> objects.
399 However, the <i> Geom2d</i> package essentially provides data structures and not algorithms.
400 You can refer to the <i> GCE2d </i> package to find more evolved construction algorithms for <i> Geom2d </i> objects.
402 @subsection OCCT_TOVW_SECTION_3_2 3D Geometry Types
404 The <i> Geom</i> package provides an implementation of 3D geometric objects complying with
405 STEP, part 42. In particular, it provides functions for:
407 * description of points, vectors, curves and surfaces,
408 * their positioning in 3D space using axis or coordinate systems, and
409 * their geometric transformation, by applying translations, rotations, symmetries, scaling transformations and combinations thereof.
411 The key characteristic of Geom curves and surfaces is that they are parameterized.
412 Each class provides functions to work with the parametric equation of the curve or
413 surface, and, in particular, to compute:
415 * the point of parameter u on a curve, or
416 * the point of parameters (u, v) on a surface.
418 together with the derivative vectors of order 1, 2, ... N at this point.
420 As a consequence of this parameterization, a Geom curve or surface is naturally oriented.
422 Parameterization and orientation differentiate elementary Geom curves and surfaces from the classes of the same (or similar) names found in the <i> gp</i> package.
423 The <i>Geom</i> package also provides conversion functions to transform a Geom object into a <i> gp</i> object, and vice-versa, when such transformation is possible.
425 Moreover, the <i> Geom </i>package provides more complex curves and surfaces, including:
426 * Bezier and BSpline curves and surfaces,
427 * swept surfaces, for example surfaces of revolution and surfaces of linear extrusion,
428 * trimmed curves and surfaces, and
429 * offset curves and surfaces.
431 Geom objects are organized according to an inheritance structure over several levels.
432 Thus, a sphere (concrete class <i> Geom_SphericalSurface</i>) is also an elementary surface and inherits from the abstract class <i> Geom_ElementarySurface</i>, while a Bezier surface (concrete class <i> Geom_BezierSurface</i>) is also a bounded surface and inherits from the abstract class <i> Geom_BoundedSurface</i>; both these examples are also surfaces (abstract class <i> Geom_Surface</i>). Curves, points and vectors inherit from the abstract class <i> Geom_Geometry,</i> which describes the properties common to any geometric object from the <i>Geom</i> package.
434 This inheritance structure is open and it is possible to describe new objects, which inherit from those provided in the Geom package, on the condition that they respect the behavior of the classes from which they are to inherit.
436 Finally, Geom objects can be shared within more complex data structures. This is why they are used within topological data structures, for example.
438 The <i> Geom</i> package uses the services of the <i> gp</i> package to:
439 * implement elementary algebraic calculus and basic analytic geometry,
440 * describe geometric transformations which can be applied to Geom objects,
441 * describe the elementary data structures of Geom objects.
443 However, the Geom package essentially provides data structures and not algorithms.
444 You can refer to the <i> GC</i> package to find more evolved construction algorithms for
448 ### Adaptors for Curves and Surfaces
450 Some Open CASCADE Technology general algorithms may work theoretically on numerous types of curves or surfaces.
451 To do this, they simply get the services required of the analysed curve or surface through an interface so as to a single API, whatever the type of curve or surface. These interfaces are called adaptors.
452 For example, <i> Adaptor3d_Curve </i> is the abstract class which provides the required services by an algorithm which uses any 3d curve.
454 <i> GeomAdaptor </i>package provides interfaces:
457 * On a curve lying on a Geom surface;
460 <i> Geom2dAdaptor</i> package provides interfaces :
462 * On a <i>Geom2d</i> curve.
464 <i> BRepAdaptor </i> package provides interfaces:
469 When you write an algorithm which operates on geometric objects, use <i> Adaptor3d</i> (or <i> Adaptor2d</i>) objects.
470 As a result, you can use the algorithm with any kind of object,
471 if you provide for this object, an interface derived from *Adaptor3d* or *Adaptor2d*.
472 These interfaces are easy to use: simply create an adapted curve or surface from a *Geom2d* curve,
473 and then use this adapted curve as an argument for the algorithm which requires it.
476 @subsection OCCT_TOVW_SECTION_3_3 Geometry Utilities
478 This library provides standard high-level functions in 2D and 3D geometry such as:
480 * Direct construction of algorithms;
481 * Approximation of curves and surfaces from points;
482 * Conversion of more elementary geometry to BSpline curves and surfaces;
483 * Calculation of points on a 2D or 3D curve;
484 * Calculation of extrema between two geometries.
486 ### Direct Construction
488 The <i> gp</i>, <i> Geom2d</i> and <i> Geom</i> packages describe elementary data structures of simple geometric
489 objects. The constructors of these objects are elementary: the construction arguments
490 are fields by which the objects are represented in their data structure.
493 On the other hand, the <i> gce</i>, <i> GCE2d</i> and <i> GC</i> packages provided
494 by the Direct Construction component construct the same types of objects
495 as <i> gp</i>, <i> Geom2d </i>and <i> Geom</i> respectively.
496 However, the former implement geometric construction algorithms that translate the
497 constructor's arguments into the data structure specific to each object.
500 Algorithms implemented by these packages are simple: there is no creation of objects
501 defined by advanced positional constraints (for more information on this subject,
502 see <i> Geom2dGcc</i> and <i> GccAna</i> which describe geometry by constraints).
505 <i> gce</i>, <i> GCE2d</i> and <i> GC </i>each offer a series of classes of construction algorithms.
508 For example, the class <i>gce_MakeCirc</i> provides a framework
509 for defining eight problems encountered in the geometric construction of circles,
510 and implementing the eight related construction algorithms.
512 The object created (or implemented) is an algorithm which can be consulted to find out, in particular:
514 * its result, which is a <i>gp_Circ</i>, and
515 * its status. Here, the status indicates whether or not the construction was successful.
517 If it was unsuccessful, the status gives the reason for the failure.
520 gp_Pnt P1 (0.,0.,0.);
521 gp_Pnt P2 (0.,10.,0.);
522 gp_Pnt P3 (10.,0.,0.);
523 gce_MakeCirc MC (P1,P2,P3);
525 const gp_Circ& C = MC.Value();
529 In addition, <i> gce</i>, <i> GCE2d</i> and <i> GC</i> each have a <i>Root</i> class. This class is the root of
530 all the classes in the package which return a status. The returned status (successful
531 construction or construction error) is described by the enumeration <i> gce_ErrorType</i>.
533 Note: classes which construct geometric transformations do not return a status, and
534 therefore do not inherit from Root.
538 Approximation of Curves and Surfaces groups together a variety of functions used in 2D and 3D geometry for:
540 * the interpolation of a set of 2D points using a 2D BSpline or Bezier curve;
541 * the approximation of a set of 2D points using a 2D BSpline or Bezier curve;
542 * the interpolation of a set of 3D points using a 3D BSpline or Bezier curve, or a BSpline surface;
543 * the approximation of a set of 3D points using a 3D BSpline or Bezier curve, or a BSpline surface.
545 You can program approximations in two ways:
547 * Using high-level functions, designed to provide a simple method for obtaining approximations with minimal programming,
548 * Using low-level functions, designed for users requiring more control over the approximations.
550 The low-level functions provide a second API with functions to:
552 * Define compulsory tangents for an approximation. These tangents have origins and extremities.
553 * Approximate a set of curves in parallel to respect identical parameterization.
554 * Smooth approximations. This is to produce a faired curve.
556 The classes <i> AppDef_MultiPointConstraints</i> and <i> AppDef_MultiLines </i> allow organizing the data.
557 The classes <i> AppDef_Compute</i>, <i> AppDef_BSplineCompute</i> and <i> AppDef_TheVariational </i>
558 classes perform the approximation itself using Bezier curves, BSpline curves, and smooth BSpline curves, respectively.
560 You can also find functions to compute:
562 * The minimal box which includes a set of points
563 * The mean plane, line or point of a set of coplanar, collinear or coincident points.
565 ### Conversion to and from BSplines
567 The Conversion to and from BSplines component has the following two distinct purposes:
568 * Firstly, it provides a homogenous formulation which can be used to describe any curve or surface.
569 This is useful for writing algorithms for a single data structure model.
570 The BSpline formulation can be used to represent most basic geometric objects provided
571 by the components which describe geometric data structures ("Fundamental Geometry Types", "2D Geometry Types" and "3D Geometry Types" components).
572 * Secondly, it can be used to divide a BSpline curve or surface into a series of curves or surfaces,
573 thereby providing a higher degree of continuity. This is useful for writing algorithms
574 which require a specific degree of continuity in the objects to which they are applied.
575 Discontinuities are situated on the boundaries of objects only.
577 The "Conversion to and from BSplines" component is composed of three packages.
579 The <i> Convert </i> package provides algorithms to convert the following into a BSpline curve or surface:
581 * a bounded curve based on an elementary 2D curve (line, circle or conic) from the <i> gp </i> package,
582 * a bounded surface based on an elementary surface (cylinder, cone, sphere or torus) from the <i> gp</i> package,
583 * a series of adjacent 2D or 3D Bezier curves defined by their poles.
585 These algorithms compute the data needed to define the resulting BSpline curve or surface.
586 This elementary data (degrees, periodic characteristics, poles and weights, knots and multiplicities)
587 may then be used directly in an algorithm, or can be used to construct the curve or the surface
588 by calling the appropriate constructor provided by the classes <i>Geom2d_BSplineCurve, Geom_BSplineCurve </i> or <i>Geom_BSplineSurface</i>.
590 The <i>Geom2dConvert</i> package provides the following:
592 * a global function which is used to construct a BSpline curve from a bounded curve based on a 2D curve from the Geom2d package,
593 * a splitting algorithm which computes the points at which a 2D BSpline curve should be cut in order to obtain arcs with the same degree of continuity,
594 * global functions used to construct the BSpline curves created by this splitting algorithm, or by other types of segmentation of the BSpline curve,
595 * an algorithm which converts a 2D BSpline curve into a series of adjacent Bezier curves.
597 The <i> GeomConvert</i> package also provides the following:
599 * a global function used to construct a BSpline curve from a bounded curve based on a curve from the Geom package,
600 * a splitting algorithm, which computes the points at which a BSpline curve should be cut in order to obtain arcs with the same degree of continuity,
601 * global functions to construct BSpline curves created by this splitting algorithm, or by other types of BSpline curve segmentation,
602 * an algorithm, which converts a BSpline curve into a series of adjacent Bezier curves,
603 * a global function to construct a BSpline surface from a bounded surface based on a surface from the Geom package,
604 * a splitting algorithm, which determines the curves along which a BSpline surface should be cut in order to obtain patches with the same degree of continuity,
605 * global functions to construct BSpline surfaces created by this splitting algorithm, or by other types of BSpline surface segmentation,
606 * an algorithm, which converts a BSpline surface into a series of adjacent Bezier surfaces,
607 * an algorithm, which converts a grid of adjacent Bezier surfaces into a BSpline surface.
611 The Making Points on Curves component comprises high level functions providing an Application Programming Interface for complex algorithms that compute points on a 2D or 3D curve. The functions use various methods.
613 The algorithms result in the following:
615 * a point on a curve, situated at a given curvilinear distance from another point on the curve
616 * a distribution of points situated at constant curvilinear intervals along a curve
617 * a distribution of points at a constant rise (i.e. respecting a criterion of maximum rise between the curve and the polygon that results from the computed points) along a curve
618 * the length of a curve.
620 @subsection OCCT_TOVW_SECTION_3_4 Topology
622 Topological library allows you to build pure topological data structures..
624 Topology defines relationships between simple geometric entities. In this way,
625 you can model complex shapes as assemblies of simpler entities.
626 Due to a built-in non-manifold (or mixed-dimensional) feature, you can build models mixing:
628 * 0D entities such as points;
629 * 1D entities such as curves;
630 * 2D entities such as surfaces;
631 * 3D entities such as volumes.
633 You can, for example, represent a single object made of several distinct bodies
634 containing embedded curves and surfaces connected or non-connected to an outer boundary.
636 Abstract topological data structure describes a basic entity - a shape,
637 which can be divided into the following component topologies:
639 * Vertex - a zero-dimensional shape corresponding to a point in geometry;
640 * Edge - a shape corresponding to a curve, and bound by a vertex at each extremity;
641 * Wire - a sequence of edges connected by their vertices;
642 * Face - part of a plane (in 2D geometry) or a surface (in 3D geometry) bounded by a closed wire;
643 * Shell - a collection of faces connected by some edges of their wire boundaries;
644 * Solid - a part of 3D space bound by a shell;
645 * Compound solid - a collection of solids.
647 The wire and the solid can be either infinite or closed.
649 A face with 3D underlying geometry may also refer to a collection of connected triangles
650 that approximate the underlying surface. The surfaces can be undefined
651 leaving the faces represented by triangles only. If so, the model is purely polyhedral.
653 Topology defines the relationship between simple geometric entities,
654 which can thus be linked together to represent complex shapes.
656 Abstract Topology is provided by six packages.
657 The first three packages describe the topological data structure used in Open CASCADE Technology:
659 * <i> TopAbs</i> package provides general resources for topology-driven applications. It contains enumerations that are used to describe basic topological notions: topological shape, orientation and state. It also provides methods to manage these enumerations.
660 * <i> TopLoc </i>package provides resources to handle 3D local coordinate systems: <i> Datum3D</i>and <i> Location</i>. <i> Datum3D</i> describes an elementary coordinate system, while <i> Location</i> comprises a series of elementary coordinate systems.
661 * <i> TopoDS</i> package describes classes to model and build data structures that are purely topological.
663 Three additional packages provide tools to access and manipulate this abstract topology:
665 * <i> TopTools</i> package provides basic tools to use on topological data structures.
666 * <i> TopExp</i> package provides classes to explore and manipulate the topological data structures described in the TopoDS package.
667 * <i> BRepTools </i> package provides classes to explore, manipulate, read and write BRep data structures. These more complex data structures combine topological descriptions with additional geometric information, and include rules for evaluating equivalence of different possible representations of the same object, for example, a point.
669 @subsection OCCT_TOVW_SECTION_3_5 Properties of Shapes
671 ### Local Properties of Shapes
673 <i>BRepLProp</i> package provides the Local Properties of Shapes component,
674 which contains algorithms computing various local properties on edges and faces in a BRep model.
676 The local properties which may be queried are:
678 * for a point of parameter u on a curve which supports an edge :
680 * the derivative vectors, up to the third degree,
681 * the tangent vector,
683 * the curvature, and the center of curvature;
684 * for a point of parameter (u, v) on a surface which supports a face :
686 * the derivative vectors, up to the second degree,
687 * the tangent vectors to the u and v isoparametric curves,
689 * the minimum or maximum curvature, and the corresponding directions of curvature;
690 * the degree of continuity of a curve which supports an edge, built by the concatenation of two other edges, at their junction point.
692 Analyzed edges and faces are described as <i> BRepAdaptor</i> curves and surfaces,
693 which provide shapes with an interface for the description of their geometric support.
694 The base point for local properties is defined by its u parameter value on a curve, or its (u, v) parameter values on a surface.
696 ### Local Properties of Curves and Surfaces
699 The "Local Properties of Curves and Surfaces" component provides algorithms for computing various local
700 properties on a Geom curve (in 2D or 3D space) or a surface. It is composed of:
702 * <i> Geom2dLProp</i> package, which provides local properties on 2D curves
703 * <i> GeomLProp </i> package, which provides local properties on 3D curves and surfaces
704 * <i> LProp </i> package, which provides an enumeration used to characterize a particular point on a 2D curve.
706 Curves are either <i> Geom_Curve </i> curves (in 3D space) or <i> Geom2d_Curve </i> curves (in the plane).
707 Surfaces are <i> Geom_Surface </i> surfaces. The point on which local properties are calculated
708 is defined by its u parameter value on a curve, and its (u,v) parameter values on a surface.
710 It is possible to query the same local properties for points as mentioned above, and additionally for 2D curves:
712 * the points corresponding to a minimum or a maximum of curvature;
713 * the inflection points.
715 ### Global Properties of Shapes
717 The Global Properties of Shapes component provides algorithms for computing the global
718 properties of a composite geometric system in 3D space, and frameworks to query the computed results.
720 The global properties computed for a system are :
725 * moment about an axis,
726 * radius of gyration about an axis,
727 * principal properties of inertia such as principal axis, principal moments, and principal radius of gyration.
729 Geometric systems are generally defined as shapes. Depending on the way they are analyzed, these shapes will give properties of:
731 * lines induced from the edges of the shape,
732 * surfaces induced from the faces of the shape, or
733 * volumes induced from the solid bounded by the shape.
735 The global properties of several systems may be brought together to give the global properties of the system composed of the sum of all individual systems.
737 The Global Properties of Shapes component is composed of:
738 * seven functions for computing global properties of a shape: one function for lines, two functions for surfaces and four functions for volumes. The choice of functions depends on input parameters and algorithms used for computation (<i>BRepGProp</i> global functions),
739 * a framework for computing global properties for a set of points (<i>GProp_PGProps</i>),
740 * and a general framework to bring together the global properties retained by several more elementary frameworks, and provide a general programming interface to consult computed global properties.
742 @subsection OCCT_TOVW_SECTION_3_6 Examples
744 ### How to compute the curve length
746 To compute curve length, use the method <i>AbscissaPoint::Length</i> from <i> GCPnts</i>.
748 This function is used only for initializing a framework to compute the length of a curve (or a series of curves).
750 The adapted curves are:
752 * Adaptor_Curve2d for 2D curves
753 * Adaptor_Curve for 3D curves.
755 The adapted curve is created in the following way:
760 Handle(Geom2d_Curve) mycurve = ... ;
761 Geom2dAdaptor_Curve C (mycurve) ;
767 Handle(Geom_Curve) mycurve = ... ;
768 GeomAdaptor_Curve C (mycurve) ;
772 The length of the curve is then computed using this curve object:
775 GCPnts_AbscissaPoint myAlgo () ;
776 Standard_Real L = myAlgo.Length( C ) ;
779 ### How to check the surface concavity
781 To check the concavity of a surface, proceed as follows:
783 1. Sample the surface and compute at each point the Gaussian curvature.
784 2. If the value of the curvature changes of sign, the surface is concave or convex depending on the point of view.
785 3. To compute a Gaussian curvature, use the class <i> SLprops</i> from <i> GeomLProp</i>, which instantiates the generic class <i> SLProps </i>from <i> LProp</i> and use the method <i> GaussianCurvature</i>.
787 ### How to approximate a curve with respect to tangencies
790 To approximate a curve with respect to tangencies, follow these steps:
792 1. Create an object of type <i> AppDef_MultiPointConstraints</i> from the set of points to approximate and use the method <i> SetTang </i>to set the tangency vectors.
793 2. Create an object of type <i> AppDef_MultiLine </i>from the <i> AppDef_MultiPointConstraint</i>.
794 3. Use <i> AppDef_BSplineCompute</i>, which instantiates <i>Approx_BSplineComputeLine</i> to perform the approximation.
796 ### How to extract the underlying geometry from shapes
799 To extract the underlying geometry from a Shape, use the following methods:
801 * <i> BRep_Tool::Surface</i> to get the geometric surface from a face.
802 * <i> BRep_Tool::Curve</i> to get the 3d geometric curve from an edge.
803 * <i> BRep_Tool::CurveOnSurface</i> to get the 2d geometric curve of an edge, defined in the parametric space of a face.
804 * <i> BRep_Tool::Pnt </i> to get the 3D point from a vertex.
806 Some of these methods have a location as argument.
808 For example, when you use <i> S1 = BRep_Tool::Surface(F,L), </i> you then get the surface stored in <i> TShape</i>.
810 To use this surface in the same position as the face, you have to apply
811 a transformation to it corresponding to the location of the face as follows:
818 The same method used without location as argument is <i>S3 = BRep_Tool : : Surface(F)</i>
819 returns a Surface in position, according to the location. S3 and S2 are geometrically equivalent surfaces.
821 Warning: with the first method, you get a pointer on the surface stored in the shape.
822 Do not modify the surface because you will modify the shape and may produce an inconsistent model.
823 With the second method, you get a copy of the surface on which the location has been applied.
824 Note: you can use also a topological object directly just as if it
825 were a geometric one by using the services of <i> BRepAdaptor </i>classes.
827 ### How to get the coordinates of a vertex
830 To recover the UV coordinates of vertices,
831 use <i> BRep_Tool::Parameters const TopoDS_Vertex& V,const TopoDS_Face& F), </i>
832 which returns the U and V parameters of the vertex V on the face F as a <i> gp_Pnt2d</i>.
834 ### How to explore a Wire
837 To explore the edges of a wire in a contiguous order, use <i> BrepTools_WireExplorer</i> class.
840 TopoDS_Wire myWire =&ldots;.
841 BRepTools_WireExplorer Ex;
842 for (Ex.Init(myWire); Ex.More(); Ex.Next()) {
843 TopoDS_Edge currentedge = Ex.Current();
844 // Process current edge
848 ### How to merge bspline curves
851 To merge joined bspline curves use the following methods:
854 void GeomConvert::ConcatG1
855 TColGeom_Array1OfBSplineCurve& ArrayOfCurves,
856 const TColStd_Array1OfReal& ArrayOfToler,
857 Handle(TColGeom_HArray1OfBSplineCurve) & ArrayOfConcatenated,
858 const Standard_Boolean ClosedG1Flag,
859 const Standard_Real ClosedTolerance)
862 This method concatenates according to G1 (tangency continuity along the curve) the
863 <i>ArrayOfCurves</i> as far as possible. The following arguments are used:
865 * <i> ArrayOfCurves</i> must have dimension bounds [0, N-1], N * number of curves to be merged.
866 * <i> ArrayOfToler</i> contains the biggest tolerance of the two points shared by two consecutive curves. Its dimension is: [0, N-2].
867 * <i> ArrayOfConcatenated</i> contains results of operation: one or more, when impossible to merge all curves from <i> ArrayOfCurves </i> into one, new bspline curves are created.
868 * <i> ClosedG1Flag </i> indicates if the <i> ArrayOfCurves </i> is closed or not.
869 * If <i> ClosedG1Flag = Standard_True, ClosedTolerance </i> contains the biggest tolerance of the two points which are at the closure, otherwise its value is 0.0.
872 void GeomConvert::ConcatC1
873 TColGeom_Array1OfBSplineCurve& ArrayOfCurves,
874 const TColStd_Array1OfReal& ArrayOfToler,
875 Handle(TColStd_HArray1OfInteger)& ArrayOfIndices,
876 Handle(TColGeom_HArray1OfBSplineCurve)& ArrayOfConcatenated,
877 const Standard_Boolean ClosedG1Flag,
878 const Standard_Real ClosedTolerance,
879 const Standard_Real AngularTolerance)
882 This method concatenates according to C1 (first derivative continuity along the curve) the <i>
883 ArrayOfCurves</i> as far possible. The following arguments are used (additionally to the mentioned above):
885 * <i> ArrayOfIndices</i> contains indices that define curves from <i> ArrayOfCurves</i> which are beginning curves for each group of curves merged into a new curve.
886 * <i> AngularTolerance</i> is used to check the continuity of tangencies.
889 void GeomConvert::ConcatC1
890 TColGeom_Array1OfBSplineCurve& ArrayOfCurves,
891 const TColStd_Array1OfReal& ArrayOfToler,
892 Handle(TColStd_HArray1OfInteger)& ArrayOfIndices,
893 Handle(TColGeom_HArray1OfBSplineCurve)& ArrayOfConcatenated,
894 const Standard_Boolean ClosedG1Flag,
895 const Standard_Real ClosedTolerance)
897 This method is the same as the previous one, except for that <i> AngularTolerance = Precision::Angular() </i>
899 It is also possible to use class <i> GeomConvert_CompCurveToBSplineCurve</i>.
900 This class provides methods to concatenate several restricted curves to a bspline curve.
901 Non-bspline curves are converted to bspline before concatenation.
905 GeomConvert_CompCurveToBSplineCurve::
906 GeomConvert_CompCurveToBSplineCurve(const Handle(Geom_BoundedCurve)& BasisCurve, const Convert_ParameterisationType Parameterization)
907 BasisCurve * beginning curve;
910 Parameterization defines the ways of conversion in bspline (by default <i> Convert_TgtThetaOver2</i>).
912 The method to add a new curve is:
914 Standard_Boolean GeomConvert_CompCurveToBSplineCurve::
915 Add(const Handle(Geom_BoundedCurve)& NewCurve,
916 const Standard_Real Tolerance,
917 const Standard_Boolean After,
918 const Standard_Boolean WithRatio,
919 const Standard_Integer MinM)
922 It returns False if the curve is not C0 with the <i> BSplineCurve</i>.
924 Tolerance is used to check the continuity and decrease the Multiplicity
925 at the common Knot until <i> MinM </i>. If <i> MinM = 0 </i>, the common Knot can be removed.
927 The parameter after defines the place for a new curve when it is possible to put
928 the new curve before or after the <i> BasisCurve</i> (in fact, it is case when concatenated curve can be closed).
929 It does not change the shape of the curve, but defines its first and last points.
931 If <i> WithRatio = Standard_True </i> the algorithm tries to reach C1 continuity.
933 The method to get a result is <i> Handle(Geom_BSplineCurve) GeomConvert_CompCurveToBSplineCurve::BSplineCurve() const </i>
935 @section OCCT_TOVW_SECTION_4 Modeling Algorithms
937 Modeling Algorithms module groups a wide range of
938 topological algorithms used in modeling and geometric algorithms, called by them.
940 These services are organized into the following libraries:
944 * Construction of Primitives
946 * Fillets and Chamfers
949 * Hidden Line Removal
952 @image html /technical_overview/images/technical_overview_ma.png
953 @image latex /technical_overview/images/technical_overview_ma.png
955 The technical overview provides only a basic description of the libraries.
956 Please, refer for more details to Modeling Algorithms User's guide
958 See also: our web site at E-learning and Training.
960 @subsection OCCT_TOVW_SECTION_4_1 Geometric Tools
962 This library provides algorithms to:
964 * Calculate the intersection of two 2D curves, surfaces, or a 3D curve and a surface;
965 * Project points onto 2D and 3D curves, points onto surfaces, and 3D curves onto surfaces;
966 * Construct lines and circles from constraints;
967 * Construct curves and surfaces from constraints;
968 * Construct curves and surfaces by interpolation
970 OPEN CASCADE company also provides a product known as Surfaces from Scattered Points
971 (SSP), which allows constructing surfaces from scattered points. This algorithm accepts
972 or constructs an initial B-Spline surface and looks for its deformation (finite elements
973 method) which would satisfy the constraints. Using optimized computation methods,
974 this algorithm is able to construct a surface from more than 500 000 points.
976 SSP product is not supplied with Open CASCADE Technology, but can be purchased separately.
978 @subsubsection OCCT_TOVW_SECTION_4_1_1 Intersections
980 The Intersections component is used to compute intersections between 2D or 3D geometrical
983 * the intersections between two 2D curves
984 * the self-intersections of a 2D curve
985 * the intersection between a 3D curve and a surface
986 * the intersection between two surfaces.
988 @subsubsection OCCT_TOVW_SECTION_4_1_2 Projections
990 The Projections component provides functionality for 2D and 3D geometry objects for computing the following:
992 * the projections of a 2D point onto a 2D curve
993 * the projections of a 3D point onto a 3D curve or surface
994 * the projection of a 3D curve onto a surface.
995 * the planar curve transposition from the 3D to the 2D parametric space of an underlying plane and v. s.
996 * the positioning of a 2D gp object in the 3D geometric space.
998 @subsubsection OCCT_TOVW_SECTION_4_1_3 Lines and Circles from Constraints
1000 The Lines and Circles from Constraints component provides numerous
1001 construction algorithms for 2D circles or lines described with numeric or
1002 geometric constraints in relation to other curves. These constraints enable the following to be imposed:
1004 * the radius of a circle,
1005 * the angle that a straight line makes with another straight line,
1006 * the tangency of a straight line or circle in relation to a curve,
1007 * the passage of a straight line or circle through a point,
1008 * the circle with center in a point or curve.
1010 For example, these algorithms enable to easily construct a circle of a given radius,
1011 centered on a straight line and tangential to another circle.
1013 The implemented algorithms are more complex than those provided
1014 by the Direct Constructions component for building 2D circles or lines.
1016 The expression of a tangency problem generally leads to several results, according
1017 to the relative positions of the solution and the circles or straight lines in relation
1018 to which the tangency constraints are expressed. For example, consider the following
1019 case of a circle of a given radius (a small one) which is tangential to two secant
1022 @image html /technical_overview/images/technical_overview_occ_0005.png "Example of a Tangency Constraint"
1023 @image latex /technical_overview/images/technical_overview_occ_0005.png "Example of a Tangency Constraint"
1025 This diagram clearly shows that there are 8 possible solutions.
1027 In order to limit the number of solutions, we can try to express the relative position
1028 of the required solution in relation to the circles to which it is tangential. For
1029 example, if we specify that the solution is inside the circle C1 and outside the
1030 circle C2, only two solutions referenced 3 and 4 on the diagram respond to the problem
1033 This technique of qualification of a solution, in relation to the curves to which
1034 it is tangential, can be used in all algorithms for constructing a circle or a straight
1035 line by geometric constraints. Four qualifiers are used, which specify the following:
1037 * the solution(s) must enclose the argument, or
1038 * the solution(s) must be enclosed by the argument, or
1039 * the solution(s) and the argument must be external to one another, or
1040 * the relative position is not qualified, i.e. all solutions apply.
1042 These definitions are very easy to interpret on a circle, where it is easy to identify
1043 the interior and exterior sides. In fact, for any kind of curve the interior is defined
1044 as the left-hand side of the curve in relation to its orientation.
1046 OCCT implements several categories of algorithms:
1048 * analytic algorithms, where solutions are obtained by the resolution of an equation, such algorithms are used when the geometries which are worked on (tangency arguments, position of the center, etc.) are points, lines or circles;
1049 * geometric algorithms, where the solution is generally obtained by calculating the intersection of parallel or bisecting curves built from geometric arguments;
1050 * iterative algorithms, where the solution is obtained by a process of iteration.
1052 For each kind of geometric construction of a constrained line or circle, OCCT provides
1053 two types of access to the user:
1055 * algorithms from the package <i> Geom2dGcc </i> automatically select the algorithm best suited to the problem to be treated, both in the general case and in all types of specific cases; the arguments used are Geom2d objects; the solutions computed are <i> gp </i> objects;
1056 * algorithms from the package <i> GccAna</i> resolve the problem analytically, and can only be used when the geometries to be worked on are lines or circles; the arguments used and solutions computed are <i> gp </i> objects.
1058 The provided algorithms compute all solutions, which correspond to the stated geometric
1059 problem, unless the solution is found by an iterative algorithm.
1061 Iterative algorithms compute only one solution, closest to an initial
1062 position. They can be used in the following cases:
1064 * to build a circle, when an argument is more complex than a line or a circle, and where
1065 the radius is not known or difficult to determine: this is the case for a circle tangential
1066 to three geometric elements, or tangential to two geometric elements and centered on a curve;
1067 * to build a line, when a tangency argument is more complex than a line or a circle.
1069 Qualified curves (for tangency arguments) are provided either by:
1071 * the <i> GccEnt</i> package, for direct use by <i> GccAna</i> algorithms, or
1072 * the <i> Geom2dGcc </i> package, for general use by <i> Geom2dGcc </i> algorithms.
1074 The <i> GccEnt</i> and <i> Geom2dGcc</i> packages also provide simple functions for building qualified curves in a very efficient way.
1076 The <i> GccAna </i>package also provides algorithms for constructing bisecting loci between
1077 circles, lines or points. Bisecting loci between two geometric objects are such that
1078 each of their points is at the same distance from the two geometric objects. They
1079 are typically curves, such as circles, lines or conics for <i> GccAna</i> algorithms.
1080 Each elementary solution is given as an elementary bisecting locus object (line, circle,
1081 ellipse, hyperbola, parabola), described by the <i>GccInt</i> package.
1083 Note: Curves used by <i> GccAna </i> algorithms to define the geometric problem to be solved,
1084 are 2D lines or circles from the <i> gp</i> package: they are not explicitly parameterized.
1085 However, these lines or circles retain an implicit parameterization, corresponding
1086 to that which they induce on equivalent Geom2d objects. This induced parameterization
1087 is the one used when returning parameter values on such curves, for instance with
1088 the functions <i> Tangency1, Tangency2, Tangency3, Intersection2</i> and <i> CenterOn3</i> provided
1089 by construction algorithms from the <i> GccAna </i> or <i> Geom2dGcc</i> packages.
1091 @subsubsection OCCT_TOVW_SECTION_4_1_4 Curves and Surfaces from Constraints
1093 The Curves and Surfaces from Constraints component groups together high level functions
1094 used in 2D and 3D geometry for:
1096 * creation of faired and minimal variation 2D curves
1097 * construction of ruled surfaces
1098 * construction of pipe surfaces
1099 * filling of surfaces
1100 * construction of plate surfaces
1101 * extension of a 3D curve or surface beyond its original bounds.
1103 #### 2D Curves from constraints
1106 Elastic beam curves have their origin in traditional methods of modeling applied
1107 in boat-building, where a long thin piece of wood, a lathe, was forced to pass
1108 between two sets of nails and in this way, take the form of a curve based on the
1109 two points, the directions of the forces applied at those points, and the properties
1110 of the wooden lathe itself.
1112 Maintaining these constraints requires both longitudinal and transversal forces to
1113 be applied to the beam in order to compensate for its internal elasticity. The longitudinal
1114 forces can be a push or a pull and the beam may or may not be allowed to slide over
1117 The class <i> Batten</i> produces curves defined on the basis of one or more constraints
1118 on each of the two reference points. These include point and angle of tangency settings.
1119 The class <i> MinimalVariation</i> produces curves with minimal variation in curvature.
1120 The exact degree of variation is provided by curvature settings.
1124 A ruled surface is built by ruling a line along the length of two curves.
1129 A pipe is built by sweeping a curve (the section) along another curve (the path).
1131 The following types of construction are available:
1132 * pipes with a circular section of constant radius,
1133 * pipes with a constant section,
1134 * pipes with a section evolving between two given curves.
1137 #### Surface filling
1139 It is often convenient to create a surface from two or more curves which will form
1140 the boundaries that define the new surface.
1142 A case in point is the intersection of two fillets at a corner. If the radius of
1143 the fillet on one edge is different from that of the fillet on another, it becomes
1144 impossible to sew together all the edges of the resulting surfaces. This leaves a
1145 gap in the overall surface of the object which you are constructing.
1147 @image html /technical_overview/images/technical_overview_occ_0006.png "Intersecting filleted edges with differing radiuses"
1148 @image latex /technical_overview/images/technical_overview_occ_0006.png "Intersecting filleted edges with differing radiuses"
1150 These algorithms allow you to fill this gap from two, three or four curves. This
1151 can be done with or without constraints, and the resulting surface will be either
1152 a Bezier or a BSpline surface in one of a range of filling styles.
1155 This package was designed with a view to handling gaps produced during fillet construction.
1156 Satisfactory results cannot be guaranteed for other uses.
1161 In CAD, it is often necessary to generate a surface which has no exact mathematical
1162 definition, but which is defined by respective constraints. These can be of a mathematical,
1163 a technical or an aesthetic order.
1166 Essentially, a plate surface is constructed by deforming a surface so that it conforms
1167 to a given number of curve or point constraints. In the figure below, you can see
1168 four segments of the outline of the plane, and a point which have been used as the
1169 curve constraints and the point constraint respectively. The resulting surface can
1170 be converted into a BSpline surface by using the function <i> MakeApprox </i>.
1173 The surface is built using a variational spline algorithm. It uses the principle
1174 of deformation of a thin plate by localised mechanical forces. If not already given
1175 in the input, an initial surface is calculated. This corresponds to the plate prior
1176 to deformation. Then, the algorithm is called to calculate the final surface. It
1177 looks for a solution satisfying constraints and minimizing energy input.
1179 @image html /technical_overview/images/technical_overview_occ_0007.png "Surface generated from four curves and a point"
1180 @image latex /technical_overview/images/technical_overview_occ_0007.png "Surface generated from four curves and a point"
1182 @image html /technical_overview/images/technical_overview_occ_0008.png "Surface generated from two curves and a point"
1183 @image latex /technical_overview/images/technical_overview_occ_0008.png "Surface generated from two curves and a point"
1185 #### Extension of a 3D curve or surface beyond its original bounds
1187 The extension is performed according to a geometric requirement and a continuity
1188 constraint. It should be a small extension with respect to the size of the original
1191 @subsubsection OCCT_TOVW_SECTION_4_1_5 Interpolation
1193 The Interpolation Laws component provides definitions of functions: <i> y=f(x) </i>.
1195 In particular, it provides definitions of:
1197 * a linear function,
1198 * an <i> S </i> function, and
1199 * an interpolation function for a range of values.
1201 Such functions can be used to define, for example, the evolution law of a fillet along the edge of a shape.
1203 The validity of the function built is never checked: the Law package does not know for what
1204 application or to what end the function will be used. In particular, if the function is used
1205 as the evolution law of a fillet, it is important that the function is always positive. The user must check this.
1207 @subsection OCCT_TOVW_SECTION_4_2 Topological Tools
1209 This library provides algorithms to:
1213 * Determine the local properties of shapes
1214 * Determine the global properties of shapes
1215 * Perform geometric transformations
1216 * Find planes in which edges are located
1217 * Convert shapes to NURBS geometry.
1219 It also furnishes a complete brep data structure for topological data structures defined
1220 in the Topology library of the Modeling Data module.
1221 This linAllows you to create standard topological objects such as:
1231 The API provides classes to build objects:
1233 * The constructors of classes provide different construction methods;
1234 * The class retains different tools used to build objects as fields;
1235 * The class provides a casting method to obtain the result automatically with a function-like call.
1237 For example, to build a vertex V on a point P, you can use:
1240 V = BRepBuilderAPI_MakeVertex(P);
1245 BRepBuilderAPI_MakeVertex MV(P);
1249 For error handling, the <i> BRepBuilderAPI</i> commands raise only the
1250 <i> 0StdFail_NotDone</i> exception. When <i> IsDone</i> is false for a command,
1251 the error description can be requested from the command.
1253 @subsection OCCT_TOVW_SECTION_4_3 Construction of Primitives
1255 This library contained in <i> BRepPrimAPI</i> package provides an API (Application Programming Interface) for:
1257 * Construction of primitives such as:
1262 * Construction by sweeping along a profile:
1264 * Rotational (through an angle of rotation).
1266 Sweeps are objects obtained by sweeping a profile along a path.
1267 The profile can be any topology and the path is usually a curve or a wire.
1268 The profile generates objects according to the following rules:
1270 * Vertices generate Edges
1271 * Edges generate Faces.
1272 * Wires generate Shells.
1273 * Faces generate Solids.
1274 * Shells generate Composite Solids.
1276 It is not allowed to sweep Solids and Composite Solids.
1278 Swept constructions along complex profiles such as
1279 BSpline curves are also available in the <i> BRepOffsetAPI </i> package.
1281 This API provides simple, high level calls for the most common operations.
1283 @subsection OCCT_TOVW_SECTION_4_4 Boolean Operations
1285 Boolean operations to create new shapes from old ones by using:
1292 There are two libraries for Boolean Operations:
1294 * Old Boolean Operations (BOA) provided by <i>BRepAlgo</i> package designed and developed in Open CASCADE 6x in 2000; its architecture and content are out of date.
1295 * New Boolean Operations (NBOA) provided by <i>BRepAlgoAPI</i> package designed and developed in 2009 and completely revised in 2013.
1297 New Boolean Operations provide the following major benefits:
1299 * The NBOA have an expandable architecture of inner sub-algorithms, which allows to create specific algorithms for the Customers using existing inner sub-algorithms as root algorithms and to reduce the time for the development.
1300 * The architecture of inner sub-algorithms of NBOA provides their reusability with maximal independence from the environment of NBOA. The fact allows to create specific algorithms for the Customers using these sub-algorithms as they are or as root classes and thus to reduce the time for the development.
1301 * The architecture of NBOA is history-based. The implementation of NBOA internally sets up a correspondence between any sub-shape of the argument and its image in the result. The history is not imposed and thus it is not error-prone as it was in BOA. The fact allows direct and safely usage of the algorithm in parametric modeling.
1302 * NBOA provide a general algorithm. It correctly processes without using the workarounds even the cases that cannot be properly processed by BOA.
1303 * The implementation of NBOA is based on NCollection classes. The usage of opportunities given by local memory allocators ( <i> NCollection_IncAllocator</i>) allows improving memory management and saving memory resources.
1304 * NBOA use modern algorithms of OCC as auxiliary tools. For e.g. the algorithm of unbalanced binary tree of overlapped bounding boxes <i> NCollection_UBTree</i>. The usage of the algorithm allows to improve the performance of NBOA if there is a big number of sub-shapes in the arguments.
1306 Boolean Operations have the following types of the arguments and produce the following results:
1307 * For arguments having the same shape type (e.g. SOLID / SOLID) the type of the resulting shape will be a COMPOUND, containing shapes of this type;
1308 * For arguments having different shape types (e.g. SHELL / SOLID) the type of the resulting shape will be a COMPOUND, containing shapes of the type that is the same as that of the low type of the argument. Example: For SHELL/SOLID the result is a COMPOUND of SHELLs.
1309 * For arguments with different shape types some of Boolean Operations can not be done using the default implementation, because of a non-manifold type of the result. Example: the FUSE operation for SHELL and SOLID can not be done, but the CUT operation can be done, where SHELL is the object and SOLID is the tool.
1310 * It is possible to perform Boolean Operations on arguments of the COMPOUND shape type. In this case each compound must not be heterogeneous, i.e. it must contain equidimensional shapes (EDGEs or/and WIREs, FACEs or/and SHELLs, SOLIDs). SOLIDs inside the COMPOUND must not contact (intersect or touch) each other. The same condition should be respected for SHELLs or FACEs, WIREs or EDGEs.
1311 * Boolean Operations for COMPSOLID type of shape are not supported.
1313 @subsection OCCT_TOVW_SECTION_4_5 Features
1315 This library contained in BRepFeat package is necessary for the creation
1316 and manipulation of both form and mechanical features in a Boundary Representation framework.
1318 The form features are depressions or protrusions including the following types:
1326 Depending on whether you wish to make a depression or a protrusion,
1327 you can choose either to remove matter (Boolean cut: Fuse equal to 0) or to add it (Boolean fusion: Fuse equal to 1).
1329 The semantics of form feature creation is based on the construction of shapes:
1331 * for a certain length in a certain direction;
1332 * up to the limiting face;
1333 * from the limiting face at a height;
1334 * above and/or below a plane.
1336 The shape defining the construction of a feature can be
1337 either a supporting edge or a concerned area of a face.
1339 In case of supporting edge, this contour can be attached to a face
1340 of the basis shape by binding. When the contour is bound to this face,
1341 the information that the contour will slide on the face becomes available
1342 to the relevant class methods. In case of the concerned area of a face, you could,
1343 for example, cut it out and move it at a different height,
1344 which will define the limiting face of a protrusion or depression.
1346 Topological definition with local operations of this sort makes calculations simpler
1347 and faster than a global operation. The latter would entail a second phase
1348 of removing unwanted matter to get the same result.
1350 Mechanical features include ribs, protrusions and grooves (or slots),
1351 depressions along planar (linear) surfaces or revolution surfaces.
1353 The semantics of mechanical features is based on giving thickness to a contour.
1354 This thickness can either be
1357 * on one side of the contour
1361 As in the semantics of form features, the thickness is defined
1362 by construction of shapes in specific contexts.
1364 However, in case of mechanical features, development contexts differ.
1365 Here they include extrusion:
1367 * to a limiting face of the basis shape;
1368 * to or from a limiting plane;
1371 @subsection OCCT_TOVW_SECTION_4_6 Hidden Line Removal
1373 This library provides two algorithms: <i> HLRBRep_Algo</i> and <i> HLRBRep_PolyAlgo</i> to define the lines of a shape hidden in a given projection. These lines can be shown or hidden to have the precision required in industrial design. To do this, the Hidden Line Removal component provides
1375 These algorithms remove or indicate lines hidden by surfaces.
1376 For a given projection, they calculate a set of lines characteristic of the object being represented. They are also used in conjunction with extraction utilities, which reconstruct a new, simplified shape from a selection of calculation results.
1377 This new shape is made up of edges, which represent the lines of the visualized shape in a plane. This plane is the projection plane.
1379 The algorithm <i> HLRBRep_Algo</i> allows working with the shape itself, while <i> HLRBRep_PolyAlgo </i>works with its polyhedral simplification. When you use <i> HLRBRep_Algo</i>, you obtain an exact result, whereas, when you use <i> HLRBRep_PolyAlgo</i>, you reduce computation time but obtain polygonal segments.
1381 @subsection OCCT_TOVW_SECTION_4_7 Shape Healing
1383 Shape Healing library provides algorithms to modify the geometry and topology of OCCT shapes.
1384 Shape Healing adapts shapes to make them maximally appropriate for use by OCCT, for example:
1386 * analyze shape characteristics and, in particular, identify the shapes that do not comply with OCCT validity rules;
1387 * fix incorrect or problem shapes;
1388 * upgrade and change shape characteristics if needed, for example a C0 supporting surface can become C1 continuous.
1390 It has several sub-domains, each with its own scope of functionality:
1392 * analysis - exploring shape properties, computing shape features, detecting violation of OCCT requirements (the shape itself is not modified);
1393 * fixing - fixing shape to meet the OCCT requirements (the shape may change its original form: modifying, removing, constructing sub-shapes, etc.);
1394 * upgrade - shape improvement for better usability in OCCT or other algorithms (the shape is replaced with a new one, but geometrically they are the same);
1395 * customization - modifying shape representation to fit specific needs (the shape is not modified, only the form of its representation is modified);
1396 * processing - mechanism of shape modification via a user-editable resource file.
1398 The technical overview provides only a basic description of the libraries. Please, refer for more details to Shape Healing User's guide
1400 See also: our web site at E-learning and Training.
1403 @subsection OCCT_TOVW_SECTION_4_8 Miscellaneous modelling algorithms.
1405 ### Fillets and Chamfers
1407 This library provides algorithms to make fillets and chamfers on shape edges.
1408 The following cases are addressed:
1410 * Corners and apexes with different radii;
1411 * Corners and apexes with different concavity.
1413 If there is a concavity, both surfaces that need to be extended and those, which do not, are processed.
1415 ### Offsets, Drafts, Sewing and Sweeps
1417 These classes provide the following services:
1419 * Creation of offset shapes and their variants such as:
1423 * Creation of tapered shapes using draft angles
1425 * Creation of sweeps
1428 @subsection OCCT_TOVW_SECTION_4_9 Examples
1430 ### How to compute the state of a point on a face:
1433 Use <i> BRepTools::Pnt </i> to get the point from your vertex.
1434 Your shape must be of the <i> TopoDS_Shape </i>type.
1435 If it is, you can use <i> BRepTopAdaptor_FClass2d </i>class. For example:
1438 BRepTopAdaptor_FClass2d::Load (to load the solid )
1439 BRepTopAdaptor_FClass2d::Perform (to compute the state of the point )
1440 BRepTopAdaptor_FClass2d::State (to get the TopAbs_State).
1444 ### How to compute the state of a point in a solid:
1447 Use <i>BRepTools::Pnt </i> to get the point from your vertex.
1448 Your shape must be of the <i> TopoDS_Solid</i> type.
1450 If it is, you can use the <i> BRepClass3d_SolidClassifier </i> class, for example:
1453 BRepClass3d_SolidClassifier::Load (to load the solid)
1454 BRepClass3d_SolidClassifier::Perform (to compute the state of the point)
1455 BRepClass3d_SolidClassifier::State (to get a TopAbs_State object)
1456 BRepClass3d_SolidClassifier inherits BRepclass3d_SClassifier
1459 ### How to connect a set of contiguous but independent faces
1462 A unique topological object can be obtained in this way using the class
1463 <i> Sewing</i> from the <i> BRepOffsetAPI </i>package which produces a shell as a result.
1466 BRepOffsetAPI_Sewing Sew;
1472 TopoDS_Shape result= Sew.SewedShape();
1475 @note The sewing algorithm uses a tolerance to assemble the faces by sewing them along common edges. You must therefore check the gap between faces before sewing or adjust the value of the tolerance according to the real gap of the geometry.
1477 If all faces have been sewed correctly, the result is a shell. Otherwise, it is a compound. After a successful sewing operation all faces have a coherent orientation.
1479 For more information, refer to the entry for this class in reference documentation.
1481 ### How to check the orientation of a solid
1483 If you want to create a solid from a closed shell, you must first check the orientation to determine if you have to reverse the shell or not (for example after creating a closed shell from a sewing operation). To do this, use the <i> PerformInfinitePoint</i> method from the <i> BrepClass3D_SolidClassifier</i> class.
1486 BRepClass3d_SolidClassifier clas3d(aShell);
1487 clas3d.PerformInfinitePoint(Precision::Confusion());
1488 if (clas3d.State() == TopAbs_IN)
1490 BRepBuilderAPI_MakeSolid aSolid(aShell);
1493 @section OCCT_TOVW_SECTION_5 Visualization
1495 Visualization in Open CASCADE Technology is based on the separation of modeling data you want to display and select, and on the graphical presentation of its structure.
1497 For visualizing data structures, OCCT provides ready-to-use algorithms, which create graphic presentations from geometric models. These data structures may be used with the viewers supplied, and can be customized to take the specificity of your application into account.
1499 Displaying is managed through presentation services, and selection in its turn is managed through selection services. With these services, data structures and algorithms are provided to display objects of an application, and to support graphical selection of these objects.
1501 Application Interactive Services (AIS) are provided to manage displaying, detection and selection of graphical presentations. These services associate data structures and interactive objects.
1503 Please, refer for more details to Visualization User's guide
1505 See also: our web site at E-learning and Training.
1507 @image html /technical_overview/images/technical_overview_viz.png
1508 @image latex /technical_overview/images/technical_overview_viz.png
1510 @subsection OCCT_TOVW_SECTION_5_1 3D Graphics
1512 3D Graphics provided by <i>Graphic3d</i> package supports three-dimensional manipulation of 3d graphic objects called structures. Structures, are made up of groups that unite primitives, such as polylines, planar polygons with or without holes, text and markers, and attributes, such as color, transparency, reflection, line type, line width, and text font.
1513 A group is the smallest editable element of a structure.
1515 A structure can be displayed, erased, highlighted and transformed.
1516 Structures can be connected to form a hierarchy of structures, composed by transformations.
1517 The viewer can perform global manipulation of structures.
1519 <i> Visual3d </i> package contains the group of classes required to implement commands for 3D viewer. The viewer manages views and light sources.
1521 Most types of primitives supported by <i> Graphic3d</i> can be dumped to a vector file format such as PDF and PostScript. Export to vector formats is implemented with help of <i> GL2PS</i> library.
1523 @subsection OCCT_TOVW_SECTION_5_2 3D Visualization
1525 This library provides services for:
1527 * Selection of 3D data structures
1528 * Presentation of 3D data structures
1530 Access to 3D presentation and selection is provided through AIS (Application Interactive Services).
1531 This package is a high-level interface that offers access to the lower-level presentation and selection services.
1532 AIS expand this underlying functionality with standard 3D selection attributes, presentation management, and standard 3D presentation attributes, and manages it in the definition of GUI viewers. To implement these services, AIS package includes the following:
1534 * Interactive context
1535 * Interactive objects
1536 * A graphic attributes manager
1539 ### Interactive Context
1541 Interactive context pilots 3D visualizations and selections.
1542 The interactive context allows you to manage, in a transparent way, graphic and "selectable" behavior of interactive objects which is not yet defined in the predefined types of these objects.
1544 AIS have two operating context types. The default neutral point type allows easily visualizing and selecting entire interactive objects, which have been loaded into the context.
1545 Opening a local context allows preparing and using a temporary selection environment to select a part of an interactive object.
1547 ### Interactive Objects
1549 Entities which are visualized and selected in the AIS viewer are objects. They connect the underlying reference geometry of a model to its graphic representation in AIS. You can use predefined OCCT classes of standard interactive objects for which all necessary functions have already been programmed, or, in case you are an advanced user, you can implement your own classes of interactive objects.
1551 ### Graphic Attributes Manager
1553 Graphic attributes manager, or AIS Drawer, stores graphic attributes for specific interactive objects and for interactive objects controlled by interactive context.
1555 Initially, all drawer attributes are filled out with the predefined values which will define the default 3D object appearance.
1557 When an interactive object is visualized, the required graphic attributes are first taken from its own drawer if one exists, or from the context drawer if no specific drawer for that type of object exists.
1559 ### Selection Filters
1561 An important aspect in selection is the filtering of entities you to select.
1562 Selection filters allow you to refine the dynamic detection context, which you want to put into effect. Some of these filters can be used at the Neutral Point, others in an open local context only. You can also program your own filters and load them into the context.
1565 @subsection OCCT_TOVW_SECTION_5_3 Application Interactive Services (AIS)
1567 Application Interactive Services provide the means to create links between an application GUI viewer and the packages which are used to manage selection and presentation. The tools AIS defined for this include different sorts of entities: the selectable viewable objects themselves and the context and attribute managers to define their selection and display.
1569 To orient the user as he works in a modeling environment, views and selections must be comprehensible.
1570 There must be several different sorts of selectable and viewable object defined.
1571 These must also be interactive, that is, connecting graphic representation and the underlying reference geometry. These entities are called Interactive Objects, and are divided into four types:
1577 The Datum groups together the construction elements such as lines, circles, points, trihedrons, plane trihedrons, planes and axes.
1578 The Relation is made up of constraints on one or more interactive shapes and the corresponding reference geometry. For example, you might want to constrain two edges in a parallel relation. This constraint is considered as an object in its own right, and is shown as a sensitive primitive. This takes the graphic form of a perpendicular arrow marked with the || symbol and lying between the two edges.
1580 The Object type includes topological shapes, and connections between shapes.
1582 None, in order not to eliminate the object, tells the application to look further until it finds an object definition in its generation which is accepted.
1584 Inside these categories, you have the possibility of an additional characterization by means of a signature. The signature provides an index to the further characterization. By default, the Interactive Object has a None type and a signature of 0 (equivalent to None.)
1585 If you want to give a particular type and signature to your interactive object, you must redefine the two virtual methods: <i> Type</i> and <i> Signature</i>.
1587 In the C++ inheritance structure of the package, each class representing a specific Interactive Object inherits <i> AIS_InteractiveObject</i>. Among these inheriting classes, <i> AIS_Relation</i> functions as the abstract mother class for inheriting classes defining display of specific relational constraints and types of dimension. Some of these include:
1589 * display of constraints based on relations of symmetry, tangency, parallelism and concentricity
1590 * display of dimensions for angles, offsets, diameters, radii and chamfers.
1592 No viewer can show everything at once with any coherence or clarity.
1593 Views must be managed carefully both sequentially and at any given instant.
1594 Another function of the view is that of a context to carry out design in.
1595 The design changes are applied to the objects in the view and then extended
1596 to the underlying reference geometry by a solver.
1597 To make sense of this complicated visual data, several display and selection tools are required.
1598 To facilitate management, each object and each construction element has a selection priority.
1599 There are also means to modify the default priority.
1601 To define an environment of dynamic detection, you can use standard filter classes or create your own.
1602 A filter questions the owner of the sensitive primitive in local context to determine
1603 if it has the desired qualities. If it answers positively, it is kept. If not, it is rejected.
1605 The standard filters supplied in AIS include:
1607 * <i> AIS_AttributeFilter</i>
1608 * <i> AIS_SignatureFilter</i>
1609 * <i> AIS_TypeFilter</i>.
1611 Only the type filter can be used in the default operating mode, the neutral point.
1612 The others can only be used in open local contexts.
1614 Neutral point and local context constitute the two operating modes of the
1615 central entity which pilots visualizations and selections, the Interactive Context.
1616 It is linked to a main viewer and if you like, a trash bin viewer as well.
1618 The neutral point, which is the default mode, allows you to easily visualize and select interactive objects which have been loaded into the context. Opening local contexts allows you to prepare and use a temporary selection environment without disturbing the neutral point.
1619 A set of functions allows you to choose the interactive objects which you want to act on, the selection modes which you want to activate, and the temporary visualizations which you will execute. When the operation is finished, you close the current local context and return to the state in which you were before opening it (neutral point or previous local context).
1621 An interactive object can have a certain number of graphic attributes, which are specific to it, such as visualization mode, color, and material. By the same token, the interactive context has a set of graphic attributes, the Drawer which is valid by default for the objects it controls.
1622 When an interactive object is visualized, the required graphic attributes are first taken from the object's own <i> Drawer</i> if one exists, or from the context drawer for the others.
1625 @subsection OCCT_TOVW_SECTION_5_4 Presentation
1627 ### Presentation Management
1629 <i> PrsMgr</i> package provides low level services and is only to be used when you do not want to use the services provided by AIS. It manages the display through the following services:
1630 * supplying a graphic structure for the object to be presented
1631 * recalculating presentations when required, e.g. by moving the object or changing its color
1632 * defining the display mode of the object to be presented; in the case of <i> AIS_Shape</i>, for example, this determines whether the object is to be displayed in wireframe (0) or shading (1) mode.
1634 Note that each new Interactive Object must have all its display modes defined.
1636 ### Presentations of Geometry
1638 The Presentations of Geometry component provides services for advanced programmers to extend the Application Interactive Services component, AIS.
1639 This would prove necessary in situations where new Interactive Objects were required.
1641 The <i> StdPrs </i>package provides standard display tools for specific geometries and topologies whereas <i> Prs3d</i> provides those for generic objects.
1642 Among these classes are definitions of the display of the specific geometry or topology in various display modes such as wireframe, shading or hidden line removal mode.
1644 ### Presentation of Dimensions
1646 <i> DsgPrs </i> package provides tools for display of dimensions, relations and XYZ trihedrons.
1648 @subsection OCCT_TOVW_SECTION_5_5 Selection
1650 Selection of 3D data structures is provided using various algorithms.
1655 The <i> SelectBasics </i>package provides the following services:
1657 * the root definition of the sensitive primitive, a selectable entity in a view
1658 * the definition of the owner of a sensitive primitive; this entity relates the primitive to the application entity which is to be selected in the view.
1660 ### Standard Selections
1663 The <i> StdSelect</i> package provides the following services:
1665 * definition of selection modes for topological shapes
1666 * definition of several filter standard <i> Selection2d.ap </i> classes
1667 * 3D viewer selectors.
1669 Note that each new Interactive Object must have all its selection modes defined.
1670 The <i>Select3D</i> package provides the following services:
1672 * definition of standard 3D sensitive primitives such as points, curves and faces;
1673 * recovery of the bounding boxes in the 2D graphic selection space, if required;
1674 * a 3D-2D projector.
1676 ### Selection Management
1679 The <i> SelectMgr</i> package provides low level services and the classes
1680 <i> SelectMgr_SelectionManager</i> and <i> SelectMgr_ViewerSelector </i>
1681 in particular are only to be used when you do not want to use the services provided by <i> AIS</i>.
1683 <i> SelectMgr </i> manages the process of dynamic selection through the following services:
1685 * activating and deactivating selection modes for Interactive Objects
1686 * adding and removing viewer selectors
1687 * definitions of abstract filter classes
1689 The principle of graphic selection consists in representing the objects which you want
1690 to select by a bounding box in the selection view.
1691 The object is selected when you use the mouse to designate the zone produced by the object.
1693 To realize this, the application creates a selection structure
1694 which is independent of the point of view. This structure is made up
1695 of sensitive primitives which have one owner object associated to each of them.
1696 The role of the sensitive primitive is to reply to the requests of the selection algorithm
1697 whereas the owner's purpose is to make the link between
1698 the sensitive primitive and the object to be selected.
1699 Each selection structure corresponds to a selection mode which defines the elements that can be selected.
1701 For example, to select a complete geometric model,
1702 the application can create a sensitive primitive for each face
1703 of the interactive object representing the geometric model.
1704 In this case, all the primitives share the same owner.
1705 On the other hand, to select an edge in a model,
1706 the application must create one sensitive primitive per edge.
1710 void InteractiveBox::ComputeSelection
1711 (const Handle(SelectMgr_Selection)& Sel,
1712 const Standard_Integer Mode){
1716 // locating the whole box by making its faces sensitive ...
1718 Handle(SelectMgr_EntityOwner) Ownr = new
1719 SelectMgr_EntityOwner(this,5);
1720 for(Standard_Integer I=1;I<=Nbfaces;I++){
1721 Sel->Add(new Select3D_SensitiveFace
1722 (Ownr,[array of the vertices] face I);
1726 case 1: // locates the edges
1729 for(Standard_Integer i=1;i<=12;i++){
1730 // 1 owner per edge...
1731 Handle(mypk_EdgeOwner) Ownr =
1732 new mypk_EdgeOwner(this,i,6);
1735 Select3D_SensitiveSegment
1736 (Ownr,firstpt(i),lastpt(i));
1743 The algorithms for creating selection structures store the sensitive primitives in a
1744 <i> SelectMgr_Selection </i> object. To do this, a set of ready-made sensitive primitives is supplied
1745 in the <i> Select2D </i>and <i> Select3D </i>packages. New sensitive primitives can be defined through inheritance
1746 from <i> SensitiveEntity</i>. For the application to make its own objects selectable,
1747 it must define owner classes inheriting <i> SelectMgr_EntityOwner</i>.
1749 For any object inheriting from <i> AIS_InteractiveObject</i>, you redefine
1750 its <i> ComputeSelection</i> functions. In the example below there are different modes
1751 of selection on the topological shape contained within the interactive object,
1752 selection of the shape itself, the vertices, the edges, the wires, the faces.
1755 void MyPack_MyClass::ComputeSelection(
1756 const Handle(SelectMgr_Selection)& aSelection,
1757 const Standard_Integer aMode)
1761 StdSelect_BRepSelectionTool::Load(
1762 aSelection,this,myShape,TopAbs_SHAPE);
1766 StdSelect_BRepSelectionTool::Load(
1767 aSelection,this,myShape,TopAbs_VERTEX);
1771 StdSelect_BRepSelectionTool::Load(
1772 aSelection,this,myShape,TopAbs_EDGE);
1776 StdSelect_BRepSelectionTool::Load(
1777 aSelection,this,myShape,TopAbs_WIRE);
1781 StdSelect_BRepSelectionTool::Load(
1782 aSelection,this,myShape,TopAbs_FACE);
1788 The <i> StdSelect_BRepSelectionTool </i> object provides a high level service
1789 which will make the shape <i> myShape</i> selectable when the <i> AIS_InteractiveContext</i> is asked to display your object.
1793 The traditional way of highlighting selected entity owners
1794 adopted by Open CASCADE Technology assumes that each entity owner
1795 highlights itself on its own. This approach has two drawbacks:
1797 * each entity owner has to maintain its own <i>Prs3d_Presentation object</i>, that results in large memory overhead for thousands of owners;
1798 * drawing selected owners one by one is not efficient from the OpenGL usage viewpoint.
1800 That is why a different method has been introduced.
1801 On the basis of <i> SelectMgr_EntityOwner::IsAutoHilight() </i> return value
1802 <i> AIS_LocalContext </i> object either uses the traditional way of highlighting
1803 ( <i> IsAutoHilight() </i> returned true) or groups such owners according to their
1804 Selectable Objects and finally calls <i> SelectMgr_SelectableObject::HilightSelected()</i> or
1805 <i> ClearSelected()</i>, passing a group of owners as an argument.
1807 Hence, an application can derive its own interactive object and redefine <i> HilightSelected()</i>,
1808 <i> ClearSelected()</i> and <i> HilightOwnerWithColor()</i> virtual methods
1809 to take advantage of such OpenGL technique as arrays of primitives.
1810 In any case, these methods should at least have empty implementation.
1812 The <i> AIS_LocalContext::UpdateSelected(const Handle(AIS_InteratciveObject)&, Standard_Boolean)
1813 </i> method can be used for efficient redrawing a selection presentation for a given interactive object from an application code.
1815 Additionally, the <i> SelectMgr_SelectableObject::ClearSelections() </i>
1816 method now accepts an optional Boolean argument.
1817 This parameter defines whether all object selections should be flagged for further update or not.
1818 This improved method can be used to re-compute an object selection (without redisplaying the object completely)
1819 when some selection mode is activated not for the first time.
1822 @subsection OCCT_TOVW_SECTION_5_6 Attribute Management
1824 The Attribute Management tool-kit provides services for advanced programmers to extend
1825 the Application Interactive Services component, AIS. This would prove necessary
1826 in situations where new Interactive Objects were required.
1828 The <i> Prs3d </i> package provides the following services:
1830 * a presentation object (the context for all modifications to the display, its presentation will be displayed in every view of an active viewer)
1831 * an attribute manager governing how objects such as color, width, and type of line are displayed; these are generic objects, whereas those in <i>StdPrs </i> are specific geometries and topologies.
1832 * generic algorithms providing default settings for objects such as points, curves, surfaces and shapes
1833 * a root object which provides the abstract framework for the DsgPrs definitions at work in display of dimensions, relations and trihedrons.
1836 @subsection OCCT_TOVW_SECTION_5_7 Mesh Visualization Services
1838 <i> MeshVS</i> (Mesh Visualization Service) component extends 3D visualization capabilities
1839 of Open CASCADE Technology. It provides flexible means of displaying meshes along with associated pre- and post-processor data.
1841 From a developer's point of view, it is easy to integrate the MeshVS component i
1842 nto any mesh-related application with the help of the following guidelines:
1844 Derive a data source class from the MeshVS_DataSource class.
1845 Re-implement its virtual methods, so as to give the <i> MeshVS</i> component access
1846 to the application data model. This is the most important part of the job,
1847 since visualization performance is affected by performance of data retrieval methods of your data source class.
1849 Create an instance of the <i> MeshVS_Mesh</i> class.
1851 Create an instance of your data source class and pass it to a <i> MeshVS_Mesh </i> object through the <i> SetDataSource()</i> method.
1853 Create one or several objects of <i> MeshVS_PrsBuilder</i>-derived classes
1854 (either standard, included in the <i> MeshVS</i> package, or your custom ones).
1855 Each <i> PrsBuilder</i> is responsible for drawing a <i> MeshVS_Mesh</i> presentation
1856 in certain display mode(s) specified as a <i> PrsBuilder</i> constructor's argument.
1857 Display mode is treated by <i> MeshVS</i> classes as a combination of bit flags
1858 (two least significant bits are used to encode standard display modes: wireframe, shading and shrink).
1859 Pass these objects to the <i> MeshVS_Mesh::AddBuilder()</i> method. <i> MeshVS_Mesh</i>
1860 takes advantage of improved selection highlighting mechanism: it highlights its selected entities itself,
1861 with the help of so called "highlighter" object. You can set one of <i> PrsBuilder</i>
1862 objects to act as a highlighter with the help of a corresponding argument of the <i> AddBuilder()</i> method.
1864 Visual attributes of the <i> MeshVS_Mesh </i> object (such as shading color, shrink coefficient and so on)
1865 are controlled through <i> MeshVS_Drawer</i> object. It maintains a map "Attribute ID --> attribute value"
1866 and can be easily extended with any number of custom attributes.
1868 In all other respects, <i> MeshVS_Mesh</i> is very similar to any other class derived
1869 from <i> AIS_InteractiveObject</i> and it should be used accordingly
1870 (refer to the description of <i> AIS package</i> in the documentation).
1872 @subsection OCCT_TOVW_SECTION_5_8 Images and Drivers
1876 The <i> Image</i> package provides <i> PseudoColorImage</i>
1877 and <i> ColorImage</i> definitions, and a set of key functions from the image fields.
1879 The <i> AlienImage</i> package allows importing images from other formats into OCCT format.
1883 The <i> Xw </i>package contains the common X graphic interface. It uses <i> XWindow </i> bitmap fonts that cannot be modified.
1885 The <i> WNT</i> package contains the common Windows NT graphic interface.
1887 The <i> Cocoa</i> package provides interaction with Cocoa API on Mac OS X.
1889 @subsection OCCT_TOVW_SECTION_5_9 New Interactive Services (NIS)
1891 New Interactive Services package provides the API similar to the traditional AIS but with some important differences/improvements:
1893 * Each type of <i> InteractiveObject</i> should have a corresponding Drawer class that defines the presentation of the Object type using direct OpenGl calls. This is a much faster way to display 3D objects, providing for more than 1 million separate selectable entities in one view.
1894 * The abstract type <i> NIS_InteractiveObject</i> does not support any properties (color, material, other aspects). The relevant properties should be defined in the specializations of the Drawer class, and the API to set/modify should be implemented in the specializations of InteractiveObject class.
1895 * Interactive selection is managed by <i> InteractiveObject</i> methods instead of special selector classes and data types. This is possible since in NIS the selection is based on 3D representation (by a ray or a box corresponding to the view direction) without intermediate 2D projection.
1896 * Many <i> InteractiveContext</i> instances can be attached to a <i> V3d_View</i>, these instances being independent containers of interactive objects; removal (detaching) of <i> InteractiveContext</i> instance destroys the contained objects.
1897 * All data types and algorithms are designed to provide the best performance for both OpenGl (server side) and application. On the other hand, the API is open to any feature supported by any version of OpenGl. This allows building custom presentations quickly and efficiently.
1898 * Standard <i> NIS_View</i> subclasses <i> V3d_View</i> thus providing all its public API, such as scene definition (view orientation, lights, background, etc.) and the standard view transformations (pan/zoom/rotate,fitAll,...). The traditional AIS-based presentations (e.g., <i> AIS_Shape</i>) are also supported, they can be rendered together with NIS presentations in the same view window.
1900 The DRAW test plugin, <i> TKViewerTest</i>, has been modified
1901 to manage <i> AIS_InteractiveContext</i> and <i> NIS_InteractiveContext</i> together in one view window.
1903 @subsection OCCT_TOVW_SECTION_5_10 Voxels
1905 A voxel is a sub-volume box with constant scalar/vector value.
1906 The object in voxel representation is split into many small sub-volumes (voxels) and its properties are distributed through voxels.
1908 Voxels are used for analysis and visualization of 3D-dimensional distribution of data.
1909 Medicine (mainly, tomography), computational physics (hydrodynamics, aerodynamics, nuclear physics)
1910 and many other industries use voxels for 3D data visualization and analysis of physical processes.
1912 Open CASCADE Technology provides several basic data containers for voxels
1913 with fast access to the data and optimal allocation of data in memory.
1914 Also, a special visualization toolkit allows visualizing voxels
1915 as colored or black/white points and cubes, displaying only the voxels visible from the user's point of view.
1917 Please, see for more information Voxels User's Guide white paper.
1919 @subsection OCCT_TOVW_SECTION_5_11 Examples
1921 ### How to change graphic attributes of an interactive object
1923 The set of graphic attributes of an interactive object is defined in AIS_Drawer.
1924 Each interactive object can have its own visualization attributes.
1926 By default, the interactive object takes the graphic attributes of
1927 the interactive context in which it is visualized
1928 (visualization mode, deflection, values for the calculation of presentations,
1929 number of isoparametric lines, color, type of line, material, etc.)
1931 In the <i> AIS_InteractiveObject</i> abstract class, several standard attributes
1932 have been privileged. These include: color, thickness of line, material, and transparency.
1933 Consequently, a certain number virtual functions which allow us to act on these attributes have been proposed.
1934 Each new class of interactive object can use them as they are or
1935 can redefine these functions to bring about the changes it should produce in the behavior of the class.
1937 Other attributes can be changed by acting directly on the drawer of the object.
1938 An interactive object has a specific drawer as soon as you change an attribute on it.
1939 If you do not modify any graphic attribute on it, the default drawer of the interactive context is referenced and used.
1941 To get the <i> AIS_Drawer</i> of an object, call method <i> AIS_InteractiveObject::Attributes </i>.
1943 To set the <i> AIS_Drawer</i> of an object, call method <i> AIS_InteractiveObject::SetLocalAttributes </i>.
1945 ### How to dump a scene from the viewer
1947 You can dump the contents of a <i> V3D_View</i> in a file with the same scale or
1948 with a different scale according to the required paper size (format)
1949 and the aspect ratio of the view. This is provided by method <i>V3d_View::Dump</i>. For example:
1952 CString filename ("myView3D.bmp");
1953 myView->Dump (filename, Aspect_FOSP_A4);
1956 <i> myView</i> is a <i> V3d_View</i>, where OCCT objects are displayed using, for example, AIS services.
1960 * The file name extension can be any among ".xwd", ".png", or ".bmp" formats both on UNIX or NT.
1961 * Be careful about dump time requirements of the resulting file, especially for the A formats.
1962 * The GIF format generates very small files, BMP and XWD generates much larger files (4 to 6 times the size of a GIF).
1963 * The time to generate these files is very short with the XWD format but 2 to 4 times longer for the other formats.
1964 * After getting an image file of your view, you can use any standard application for editing or sending the image file to a printer (i.e.: Microsoft Photo Editor on Windows or Image Viewer on SUN system)
1966 ### How to add and remove objects from Selections
1969 You can add or remove an object from a selection in one of two ways. You can use:
1971 * <i> AIS_InteractiveContext::AddOrRemoveCurrentObject</i> method at neutral points;
1972 * <i> AddOrRemoveCurrent </i> method if a local context is opened.
1975 ### How to detect overlapped objects
1978 When objects overlap each other and cause difficulties in selection,
1979 you can use the mechanism provided with the <i> AIS_InteractiveContext</i>
1980 to successively highlight all the objects found under the selection.
1981 This allows you to choose and validate the required object.
1984 If ( myAISContext->HasNextDetected()) {
1986 // if up key is pressed
1987 myAISContext ->HilightNextDetected(myView);
1989 // if down key is pressed
1990 myAISContext ->HilightPreviousDetected(myView);
1997 ### Get mouse coordinates in 3D view
2000 To switch from pixel mouse position on the screen to 3D coordinates
2001 in <i> V3d_View</i>, use <i>V3d_View::Convert</i> method.
2004 Handle(V3d_View) aview
2005 aView->Convert(Xp,Yp,X,Y,Z)
2008 Where <i> Xp</i>, <i> Yp</i> are the mouse coordinates in pixels and X,Y,Z the real coordinates in 3D space.
2010 ### 3D Viewer Objects
2012 The <i> V3d </i> package contains the set of commands and services of the 3D Viewer.
2013 It provides a set of high level commands to control views and viewing modes.
2014 This package is complementary to the <i> Visual3D</i> graphic package.
2016 <i> CSF_WALKTHROUGH</i> variable enables you to manage the perspective of the view
2017 in the viewer by defining <i> setenv CSF_WALKTHROUGH </i> "Yes".
2019 If you use the syntax <i> unsetenv CSF_WALKTHROUGH </i>, you make sure that the variable
2020 is deactivated. In this case, the eye is located outside the 3D bounding box of the view.
2021 This is the default behavior for managing the view perspective.
2023 @section OCCT_TOVW_SECTION_6 Data Exchange
2025 Data Exchange is a key factor in using Open CASCADE Technology (as well as applications based thereon)
2026 concurrently with other software such as CAD systems. It provides the openness of OCCT in a multi-software environment,
2027 by allowing it to process external data and providing a good level of integration.
2029 This means obtaining results of good quality, and covering the needs of exchanges
2030 from OCCT-based applications regardless of external data quality or requirements,
2031 in particular in respect of allowed data types and arrangements between them, accepted gaps between geometries.
2033 This matter is addressed by Data Exchange Module, which is organized in a modular way.
2035 @image html /technical_overview/images/technical_overview_de.png
2036 @image latex /technical_overview/images/technical_overview_de.png
2038 Data Exchange interfaces in OCCT allow software based on OCCT
2039 to exchange data with various CAD software, thus ensuring a good level of interoperability.
2041 Data Exchange interfaces function either in accordance with the standards (IGES, STEP),
2042 which can be used by various software packages for CAD, PDM etc., or as direct connectors to proprietary formats.
2044 ### Standardized Data Exchange
2047 * STEP (AP203 : Mechanical Design, this covers General 3D CAD; AP214: Automotive Design)
2052 Data Exchange interfaces (STEP, IGES) allow to query and examine a file,
2053 results of conversion and its validity. They are designed to support extensions (like new standards) in a common modular architecture.
2055 ### Extended data exchange
2058 Extended data exchange (XDE) allows you to extend the scope of exchange by translating
2059 additional data attached to geometric ("BREP") data, thereby improving the interoperability with external software.
2060 Data types such as colors, assembly descriptions and validation properties
2061 (i.e. center of gravity, etc.) are supported. These data are stored together with shapes in an OCAF (XCAF) document.
2064 ### Proprietary Data Exchange
2066 In addition to standard Data Exchange interfaces, separate components are available
2067 to provide direct mapping and data adaptation (using Shape Healing) with CAD software supporting the following formats:
2073 These components are based on the same architecture as interfaces with STEP and IGES.
2075 ### Translating a shape to STL Format
2078 OCCT includes a module for translating OCCT shapes to STL (Stereolithography) format.
2079 STL is a format designed for rapid prototyping.
2080 It is intended to send geometric data (volumic) to stereolithography machines,
2081 which can read and interpret such data. These machines can transform a volumic model
2082 to a physical prototype made of plastic, by using laser to coagulate material,
2083 which corresponds to the volume, and set free the material around.
2084 STL defines these surfaces by triangles.
2085 Thus, no machining is required to switch from a virtual model to a physical one.
2087 Since STL files can only include solids described by their mesh structures,
2088 OCCT shapes, which are intended to be written, must be solids,
2089 components of solids or closed shells with a correct orientation.
2091 When translating shapes to STL format, remember that all references
2092 to shapes mean references to OCCT shapes unless otherwise explicitly defined.
2093 In addition, sets of faces or unclosed shells may also be translated but visualization in foreign viewers may be incorrect.
2095 ### Translating a shape to VRML Format
2097 The Virtual Reality Modeling Language (VRML) is a language for describing multi-participant interactive simulations, virtual worlds networked via the Internet and hyperlinked with the World Wide Web. VRML is a format designed for animated visualization of solids.
2098 OCCT includes a module for translating OCCT shapes to VRML (Virtual Reality Modeling Language).
2099 OCCT shapes may be translated in two representations (states): shaded or wireframe.
2100 Since shaded VRML format files include only solids described by their mesh structures, the OCCT shapes intended to be written must be solids, components of solids or closed shells with a correct orientation.
2102 @subsection OCCT_TOVW_SECTION_6_1 General Definitions
2104 OCCT general definitions for Data Exchange include several enumerations and classes used by IGES and STEP data exchange interfaces.
2106 To define translation parameters and file headers, you can use:
2108 * <i> Interface_InterfaceModel</i>
2109 * <i> Interface_Static</i>
2111 To manage Message display, use class <i> Mesage_Messenger</i>.
2113 To define the type of analysis of the source file, and to ensure the success
2114 of the loading operation, you use the following enumerations from the <i> IFSelect</i> package:
2116 * <i> PrintCount</i>
2117 * <i> ReturnStatus</i>
2119 To read and write attributes such as names, colors, layers for IGES and STEP
2120 and validation properties and structure of assemblies for STEP, you can use an XDE document.
2122 It is possible to learn more about XDE documents from XDE User's guide
2124 See also: our web site at E-learning and Training.
2127 @subsection OCCT_TOVW_SECTION_6_2 IGES
2129 The IGES interface reads IGES files and translates them to Open CASCADE Technology models.
2130 IGES files produced in accordance with IGES standard versions up to and including version 5.3 can be read.
2131 The interface is able to translate one entity, a group of entities or a whole file.
2132 Before beginning a translation, you can set a range of parameters to manage the translation process.
2133 If you like, you can also check file consistency before translation.
2135 The IGES interface also translates OCCT models to IGES files.
2136 IGES files produced by this component conform to IGES standard version 5.3.
2138 Other kinds of data such as colors and names can be read or written
2139 with the help of XDE tools <i> IGESCAFControl_Reader</i> and <i> IGESCAFControl_Writer</i>.
2143 * an IGES model is an IGES file that has been loaded into memory.
2144 * an IGES entity is an entity in the IGES normal sense.
2145 * a root entity is the highest level entity of any given type, e.g. type 144 for surfaces and type 186 for solids. Roots are not referenced by other entities.
2147 It is possible to learn more about the IGES interface from IGES User's guide
2149 See also: our web site at E-learning and Training.
2151 @subsection OCCT_TOVW_SECTION_6_3 STEP
2153 The STEP interface reads STEP files produced in accordance with STEP Application Protocol 214
2154 (Conformance Class 2 both CD and DIS versions of schema) and translates them
2155 to Open CASCADE Technology models. STEP Application Protocol 203 is also supported.
2157 The STEP interface also translates OCCT models to STEP files. STEP files that are produced
2158 by this interface conform to STEP AP 203 or AP 214 (
2159 Conformance Class 2, either CD or DIS version of the schema) depending on the user's option.
2161 Basic interface reads and writes geometrical, topological STEP data and assembly structures.
2163 The interface is able to translate one entity, a group of entities or a whole file.
2165 Other kinds of data such as colors, validation properties, layers, names
2166 and the structure of assemblies can be read or written
2167 with the help of XDE tools - <i> STEPCAFControl_Reader</i> and <i> STEPCAFControl_Writer</i>.
2169 To choose a translation mode when exporting to a STEP format, use <i> STEPControl_STEPModelType</i>.
2171 There is a set of parameters that concern the translation and can be set before the beginning of the translation.
2174 * a STEP model is a STEP file that has been loaded into memory;
2175 * all references to shapes indicate OCCT shapes unless otherwise explicitly stated;
2176 * a root entity is the highest level entity of any given type, i.e. an entity that is not referenced by any other one.
2178 It is possible to learn more about the STEP interface from STEP User's guide
2179 See also: our web site at E-learning and Training.
2181 @subsection OCCT_TOVW_SECTION_6_4 STL
2183 The STL component translates Open CASCADE Technology shapes to STL files. STL (Stereolithography) format is widely used for rapid prototyping.
2185 As STL files can only include solids described by their mesh structure,
2186 the OCCT shapes to be written must be solids, components of solids or closed shells with a correct orientation.
2188 Note All references to shapes indicate OCCT shapes unless otherwise explicitly stated.
2190 Sets of faces or unclosed shells may also be translated to STL format but visualization with foreign viewers may be incorrect.
2192 @subsection OCCT_TOVW_SECTION_6_5 VRML
2194 The VRML component translates Open CASCADE Technology shapes to VRML 1.0 files
2195 (Virtual Reality Modeling Language). OCCT shapes may be translated in two representations:
2196 shaded or wireframe. A shaded representation present shapes as sets of triangles
2197 computed by a mesh algorithm while a wireframe representation present shapes as sets of curves.
2199 As shaded VRML format files only include solids described by their mesh structures,
2200 the OCCT shapes to be written must be solids, components of solids or closed shells with a correct orientation.
2204 * all references to shapes indicate OCCT shapes unless otherwise explicitly stated;
2205 * sets of faces or unclosed shells may also be translated to shaded VRML format but visualization with foreign viewers may be incorrect.
2207 @section OCCT_TOVW_SECTION_7 Application Framework
2209 The Application Framework uses an associativity engine to simplify the development of a CAD application.
2210 Based on application/document architecture, it does this due to the following features:
2212 * Application data is handled by the mechanism of attributes
2213 * Attributes may be organized according to your development needs
2214 * Multiple documents can be managed by an application
2215 * Ready-to-use modeling data attributes common to CAD/CAM applications
2216 * Document modification and recomputation
2217 * Data storage services
2218 * A ready-to-use Undo-Redo and Copy-Paste functions
2220 Since OCAF handles your application structure, your only major development task is the creation
2221 of application-specific data and GUIs. It is the organization of application data
2222 due to which OCAF differs from any other CAD framework. In OCAF, data structures are not shape-driven,
2223 but reference-key driven. In this respect, attributes such as shape data, color, material,
2224 are attached to a deeper invariant structure of a model than the shapes themselves.
2225 Then OCAF organizes and embeds these attributes in a document.
2226 For example, a geometry becomes the value of the Shape attribute,
2227 in the same way as a number is the value of the Integer attribute and a string is the value of the Name attribute.
2229 OCAF documents are in their turn managed by an OCAF application.
2231 Please, refer for more details to OCAF User's guide and the OCAF white papers:
2232 * Application Framework
2233 * Distribution of Data through OCAF Tree
2234 * Application Framework Function Mechanism
2236 See also: our web site at E-learning and Training.
2238 @subsection OCCT_TOVW_SECTION_7_1 How to start working with OCAF
2240 To create a useful OCAF-based application, it is necessary to redefine the following
2241 two deferred methods: <i> Formats</i> and <i> ResourcesName</i>
2243 In the <i> Formats </i> method, it is necessary to add the format
2244 of the documents to be read by the application and which may have been built in other applications.
2249 void myApplication::Formats(TColStd_SequenceOfExtendedString& Formats)
2251 Formats.Append(TCollection_ExtendedString ("OCAF-myApplication"));
2255 In the <i> ResourcesName</i> method, you only define the name of the resource file. This
2256 file contains several definitions for the saving and opening mechanisms associated
2257 with each format and calling of the plug-in file.
2260 Standard_CString myApplication::ResourcesName()
2262 return Standard_CString ("Resources");
2266 To obtain the saving and opening mechanisms, it is necessary to set two environment
2267 variables: <i> CSF_PluginDefaults</i>, which defines the path of the plug-in file and <i> CSF_ResourcesDefault</i>, which defines the resource file:
2270 SetEnvironmentVariable ( "CSF_ResourcesDefaults",myDirectory);
2271 SetEnvironmentVariable ( "CSF_PluginDefaults",myDirectory);
2274 The plugin and the resource files of the application will be located in <i> myDirector</i>.
2275 The name of the plugin file must be <i>Plugin</i>.
2279 The resource file describes the documents (type and extension) and
2280 the type of data that the application can manipulate
2281 by identifying the storage and retrieval drivers appropriate for this data.
2283 Each driver is unique and identified by a GUID generated, for example, with the <i> uuidgen </i> tool in Windows.
2285 Five drivers are required to use all standard attributes provided within OCAF:
2287 * the schema driver (ad696002-5b34-11d1-b5ba-00a0c9064368)
2288 * the document storage driver (ad696000-5b34-11d1-b5ba-00a0c9064368)
2289 * the document retrieval driver (ad696001-5b34-11d1-b5ba-00a0c9064368)
2290 * the attribute storage driver (47b0b826-d931-11d1-b5da-00a0c9064368)
2291 * the attribute retrieval driver (47b0b827-d931-11d1-b5da-00a0c9064368)
2293 These drivers are provided as plug-ins and are located in the <i> PappStdPlugin</i> library.
2296 For example, this is a resource file, which declares a new model document OCAF-MyApplication:
2299 formatlist:OCAF-MyApplication
2300 OCAF-MyApplication.Description: MyApplication Document Version 1.0
2301 OCAF-MyApplication.FileExtension: sta
2302 OCAF-MyApplication.StoragePlugin: ad696000-5b34-11d1-b5ba-00a0c9064368
2303 OCAF-MyApplication.RetrievalPlugin: ad696001-5b34-11d1-b5ba-00a0c9064368
2304 OCAF-MyApplicationSchema: ad696002-5b34-11d1-b5ba-00a0c9064368
2305 OCAF-MyApplication.AttributeStoragePlugin: 47b0b826-d931-11d1-b5da-00a0c9064368
2306 OCAF-MyApplication.AttributeRetrievalPlugin: 47b0b827-d931-11d1-b5da-00a0c9064368
2312 The plugin file describes the list of required plug-ins to run the application and the
2313 libraries in which plug-ins are located.
2315 You need at least the <i> FWOSPlugin</i> and the plug-in drivers to run an OCAF application.
2317 The syntax of each item is <i> Identification.Location Library_Name, </i> where:
2318 * Identification is GUID.
2319 * Location defines the location of the Identification (where its definition is found).
2320 * Library_Name is the name (and path to) the library, where the plug-in is located.
2322 For example, this is a Plugin file:
2325 a148e300-5740-11d1-a904-080036aaa103.Location: FWOSPlugin
2326 ! base document drivers plugin
2327 ad696000-5b34-11d1-b5ba-00a0c9064368.Location: PAppStdPlugin
2328 ad696001-5b34-11d1-b5ba-00a0c9064368.Location: PAppStdPlugin
2329 ad696002-5b34-11d1-b5ba-00a0c9064368.Location: PAppStdPlugin
2330 47b0b826-d931-11d1-b5da-00a0c9064368.Location: PAppStdPlugin
2331 47b0b827-d931-11d1-b5da-00a0c9064368.Location: PAppStdPlugin
2334 @subsection OCCT_TOVW_SECTION_7_2 Data Attributes
2336 The following ready-to-use attributes are provided:
2337 * Shape attributes, which contain shapes and their evolution
2338 * Standard attributes, a collection of common CAD/CAM attributes including:
2343 * Visualization attributes implement the Application Interactive Services in the context of Open CASCADE Application Framework.
2344 * Function attributes which regenerate any data affected by modifications made in a
2347 ### Shape Attributes
2349 A topological attribute can be seen as a hook into the topological structure. To
2350 this hook, data can be attached and references defined.
2353 It is used for keeping and access to topological objects and their evolution. All
2354 topological objects are stored in the one user-protected <i> TNaming_UsedShapes attribute</i>
2355 at the root label of the data framework. This attribute contains map with all topological
2356 shapes, used in this document.
2358 TNaming_NamedShape attribute can be added to any other attribute. This attribute contains
2359 references (hooks) to shapes from the <i> TNaming_UsedShapes</i> attribute and evolution
2360 of these shapes. <i> TNaming_NamedShape </i> attribute contains a set of pairs of hooks: old
2361 shape and new shape (see the figure below). It allows not only get the topological
2362 shapes by the labels, but also trace evolution of the shapes and correctly resolve
2363 dependent shapes by the changed one.
2365 If a shape is newly created, the old shape for the corresponding named shape is an empty
2366 shape. If a shape is deleted, then the new shape in this named shape is empty.
2368 @image html /technical_overview/images/technical_overview_shapeattrib.png
2369 @image latex /technical_overview/images/technical_overview_shapeattrib.png
2372 ### Shape attributes in data framework.
2374 Algorithms can dispose sub-shapes of the result shape at the individual
2375 label depending on necessity:
2377 * If a sub-shape must have some extra attributes (material of each face or color of each edge). In this case a specific sub-shape is placed to the separate label (usually, sub-label of the result shape label) with all attributes of this sub-shape.
2378 * If topological naming is needed, a necessary and sufficient (for selected sub-shapes identification) set of sub-shapes is placed to the child labels of the result shape label. As usual, as far as basic solids and closed shells are concerned, all faces of the shape are disposed. Edges and vertices sub-shapes can be identified as intersection of contiguous faces. Modified/generated shapes may be placed to one named shape and identified as this named shape and source named shape that also can be identified with used algorithms.
2380 <i> TNaming_NamedShape </i> may contain a few pairs of hooks with the same evolution. In this
2381 case topology shape, which belongs to the named shape, is a compound of new shapes.
2383 The data model contains both the topology and the hooks, and functions handle both
2384 topological entities and hooks. Consider the case of a box function, which creates
2385 a solid with six faces and six hooks. Each hook is attached to a face. If you want,
2386 you can also have this function create hooks for edges and vertices as well as for
2389 Not all functions can define explicit hooks for all topological entities they create,
2390 but all topological entities can be turned into hooks when necessary. This is where
2391 topological naming is necessary.
2393 Consider the following example. A box defines six hooks for the six faces, but a
2394 protrusion created on a face of the box can only define two hooks, one for the top
2395 face, and one for all the lateral faces. As the basic wire defining the protrusion
2396 may change in the future the protrusion function cannot designate the lateral faces
2397 without ambiguity, their number may change. Figure 6 illustrates this example, faces
2398 F1 to F6 of the box each have a hook. Faces F7 to F10, the lateral faces of the protrusion,
2399 share a single hook, and face F11, the top face, has one hook.
2401 @image html /technical_overview/images/technical_overview_occ_0068.png
2402 @image latex /technical_overview/images/technical_overview_occ_0068.png
2404 This structure raises two problems:
2406 * the value of the face F6 attribute-hook has changed;
2407 * no data can be attached to F7.
2409 When a hook designates multiple faces like F7-F10 (or the hook on F6 if F6 was split)
2410 it is impossible to attach data to an individual face like F7.
2412 In fact, the protrusion has a trimmed face F6. As a result, the value of this face
2413 has changed and the current value of the hook attached to it needs to be found. Note
2414 that this face could have been split in two faces (for example if the function had
2415 been a slot) and both new faces would have been attached to the same hook.
2418 ### Standard Attributes
2421 Standard attributes are already existing ready-to-use attributes, which allow you
2422 to create and modify labels and attributes for many basic data types.
2424 To find an attribute attached to a specific label, you use the GUID of the type of
2425 attribute you are looking for. For this, find this information using the method
2426 <i> GetID</i> and the method <i> Find</i> for the label as follows:
2429 Standard_GUID anID = MyAttributeClass::GetID();
2430 Standard_Boolean HasAttribute = aLabel.Find(anID,anAttribute);
2434 ### Function Attributes
2437 A model consists of data and algorithms manipulating with data. OCAF attributes store
2438 data. A Function attribute stores data corresponding to a Function (see the white
2439 paper OCAF Function Mechanism User's Guide). This mechanism manipulates with algorithms
2440 computing the model in the optimal way following the modifications.
2442 @subsection OCCT_TOVW_SECTION_7_3 Persistent Data Storage
2444 There are three schemas of persistence, which you can use to store and retrieve OCAF data (documents):
2446 * <i> Standard</i> persistence schema, compatible with previous OCAF applications
2447 * <i> XmlOcaf</i> persistence, allowing the storage of all OCAF data in XML form
2448 * <i> BinOcaf</i> persistence, allowing the storage of all OCAF data in binary format form
2451 All schemes are independent of each other, but they guarantee that the standard OCAF
2452 attributes stored and retrieved by one schema will be storable and retrievable by
2453 the other. Therefore in any OCAF application you can use any persistence schema or
2454 even all three of them. The choice is made by the Format string of stored OCAF documents
2455 or automatically by the file header data - * on retrieval.
2457 Persistent data storage in OCAF using the <i> Standard</i> package is presented in:
2459 * Basic Data Storage
2460 * Persistent Collections
2462 Persistent storage of shapes is presented in the following chapters:
2464 * Persistent Geometry
2465 * Persistent Topology
2467 Finally, information about opening and saving persistent data is presented in Standard
2471 @subsubsection OCCT_TOVW_SECTION_7_3_1 Basic Data Storage
2473 Normally, all data structures provided by Open CASCADE Technology are run-time structures,
2474 in other words, transient data. As transient data, they exist only while an application
2475 is running and are not stored permanently. However, the Data Storage module provides
2476 resources, which enable an application to store data on disk as persistent data.
2478 Data storage services also provide libraries of persistent classes and translation
2479 functions needed to translate data from transient to persistent state and vice-versa.
2481 #### Libraries of persistent classes
2483 Libraries of persistent classes are extensible libraries of elementary classes you
2484 use to define the database schema of your application. They include:
2485 * Unicode (8-bit or 16-bit character type) strings
2486 * Collections of any kind of persistent data such as arrays, stacks, queues, and graphs.
2488 All persistent classes are derived from the \b Persistent base class, which defines
2489 a unique way of creating and handling persistent objects. You create new persistent
2490 classes by inheriting from this base class.
2492 #### Translation Functions
2494 Translation functions allow you to convert persistent objects to transient ones and
2495 vice-versa. These translation functions are used to build Storage and Retrieval drivers
2498 For each class of 2D and 3D geometric types, and for the general shape class in the
2499 topological data structure library, there are corresponding persistent class libraries,
2500 which allow you to translate your data with ease.
2502 #### Creation of Persistent Classes
2504 If you are using Unix platforms as well as WOK and CDL, you can create your own persistent
2505 classes. In this case, data storage is achieved by implementing Storage and Retrieval
2508 The <i> Storage </i> package is used to write and read persistent objects.
2509 These objects are read and written by a retrieval or storage algorithm
2510 (<i> Storage_Schema </i>object) in a container (disk, memory, network ...).
2511 Drivers (<i> FSD_File</i> objects) assign a physical container for data to be stored or retrieved.
2513 The standard procedure for an application in reading a container is as follows:
2515 *open the driver in reading mode,
2516 *call the Read function from the schema, setting the driver as a parameter. This function returns an instance of the <i> Storage_Data </i> class which contains the data being read,
2519 The standard procedure for an application in writing a container is as follows:
2521 *open the driver in writing mode,
2522 *create an instance of the <i> Storage_Data </i> class, then add the persistent data to write with the function <i> AddRoot</i> ,
2523 *call the function <i> Write </i> from the schema, setting the driver and the <i> Storage_Data </i> instance as parameters,
2526 @subsubsection OCCT_TOVW_SECTION_7_3_2 Persistent Collections
2528 Persistent collections are classes which handle dynamically sized collections of
2529 data that can be stored in the database. These collections provide three categories
2532 * persistent strings,
2533 * generic arrays of data,
2534 * commonly used instantiations of arrays.
2536 Persistent strings are concrete classes that handle sequences of characters based
2537 on both ASCII (normal 8-bit) and Unicode (16-bit) character sets.
2539 Arrays are generic classes, that is, they can hold a variety of objects not necessarily
2540 inheriting from a unique root class. These arrays can be instantiated with any kind
2541 of storable or persistent object, and then inserted into the persistent data model
2542 of a user application.
2544 The purpose of these data collections is simply to convert transient data into its
2545 persistent equivalent so that it can be stored in the database. To this end, the
2546 collections are used to create the persistent data model and assure the link with
2547 the database. They do not provide editing or query capabilities because it is more
2548 efficient, within the operative data model of the application, to work with transient
2549 data structures (from the <i> TCollection</i> package).
2553 * the persistent strings only provide constructors and functions to convert between transient and persistent strings, and
2554 * the persistent data collections are limited to arrays. In other words, <i> PCollection</i> does not include sequences, lists, queues, sets, stacks and so on (unlike <i> TCollection</i>).
2556 Persistent string and array classes are found in the <i> PCollection</i> package.
2557 In addition, <i> PColStd</i> package provides standard,
2558 and frequently used, instantiations of persistent arrays, for very simple objects.
2560 @subsubsection OCCT_TOVW_SECTION_7_3_3 Persistent Geometry
2562 The Persistent Geometry component describes geometric data structures which can be
2563 stored in the database. These packages provide a way to convert data from the transient
2564 "world" to the persistent "world".
2566 Persistent Geometry consists of a set of atomic data models parallel to the geometric
2567 data structures described in the geometry packages. Geometric data models, independent
2568 of each other, can appear within the data model of any application. The system provides
2569 the means to convert each atomic transient data model into a persistent one, but
2570 it does not provide a way for these data models to share data.
2572 Consequently, you can create a data model using these components, store data in,
2573 and retrieve it from a file or a database, using the geometric components provided
2574 in the transient and persistent "worlds". In other words, you customize the system
2575 by declaring your own objects, and the conversion of the geometric components from
2576 persistent to transient and vice versa is automatically managed for you by the system.
2578 However, these simple objects cannot be shared within a more complex data model.
2579 To allow data to be shared, you must provide additional tools.
2581 Persistent Geometry is provided by several packages.
2583 The <i> PGeom</i> package describes geometric persistent objects in 3D space, such as points,
2584 vectors, positioning systems, curves and surfaces.
2586 These objects are persistent versions of those provided by the <i> Geom</i> package: for
2587 each type of transient object provided by Geom there is a corresponding type of persistent
2588 object in the <i>PGeom</i> package. In particular the inheritance structure is parallel.
2590 However the <i> PGeom </i>package does not provide any functions to construct, edit or access
2591 the persistent objects. Instead the objects are manipulated as follows:
2593 * Persistent objects are constructed by converting the equivalent transient <i> Geom </i> objects. To do this you use the <i>MgtGeom::Translate</i> function.
2594 * Persistent objects created in this way are used to build persistent data structures that are then stored in a file or database.
2595 * When these objects are retrieved from the file or database, they are converted back into the corresponding transient objects from the Geom package. To do this, you use <i>MgtGeom::Translate</i> function.
2597 In other words, you always edit or query transient data structures within the transient
2598 data model supplied by the session.
2599 Consequently, the documentation for the <i> PGeom </i> package consists simply of a list of available objects.
2601 The <i> PGeom2d </i> package describes persistent geometric objects in 2D space, such as points,
2602 vectors, positioning systems and curves. This package provides the same type of services
2603 as the <i> PGeom</i> package, but for the 2D geometric objects provided by the <i> Geom2d</i> package.
2604 Conversions are provided by the <i>MgtGeom::Translate</i> function.
2607 //Create a coordinate system
2608 Handle(Geom_Axis2Placement) aSys;
2611 //Create a persistent coordinate PTopoDS_HShape.cdlsystem
2612 Handle(PGeom_Axis2placement)
2613 aPSys = MgtGeom::Translate(aSys);
2615 //Restore a transient coordinate system
2616 Handle(PGeom_Axis2Placement) aPSys;
2618 Handle(Geom_Axis2Placement)
2619 aSys = MgtGeom::Translate(aPSys);
2623 @subsubsection OCCT_TOVW_SECTION_7_3_4 Persistent Topology
2625 The Persistent Topology component describes topological data structures which can be stored in the database. These packages provide a way to convert data from the transient "world" to the persistent "world".
2627 Persistent Topology is based on the BRep concrete data model provided by the topology packages. Unlike the components of the Persistent Geometry package, topological components can be fully shared within a single model, as well as between several models.
2629 Each topological component is considered to be a shape: a <i> TopoDS_Shape</i> object. The system's capacity to convert a transient shape into a persistent shape and vice-versa applies to all objects, irrespective of their complexity: vertex, edge, wire, face, shell, solid, and so on.
2631 When a user creates a data model using BRep shapes, he uses the conversion functions that the system provides to store the data in, and retrieve it from the database. The data can also be shared.
2633 Persistent Topology is provided by several packages.
2635 The <i> PTopoDS</i> package describes the persistent data model associated with any BRep shape; it is the persistent version of any shape of type <i> TopoDS_Shape</i>. As is the case for persistent geometric models, this data structure is never edited or queried, it is simply stored in or retrieved from the database. It is created or converted by the <i>MgtBRep::Translate</i> function.
2637 The <i> MgtBRepAbs</i> and <i> PTColStd </i> packages provide tools used by the conversion functions of topological objects.
2641 TopoDS_Shape aShape;
2643 //Create a persistent shape
2644 PtColStd_DoubleTransientPersistentMap aMap;
2646 Handle(PTopoDS_HShape) aPShape =
2647 aMap.Bind2(MgtBRep::Translate
2648 aShape,aMap,MgtBRepAbs_WithTriangle));
2652 //Restore a transient shape
2653 Handle(PTopoDS_HShape) aPShape;
2655 Handle(TopoDS_HShape) aShape =
2656 aMap.Bind1(MgtBRep::Translate
2657 (aPShape,aMap,MgtBRepAbs_WithTriangle));
2662 @subsubsection OCCT_TOVW_SECTION_7_3_5 Standard Documents
2664 Standard documents offer you a ready-to-use document containing a TDF-based data
2665 structure. The documents themselves are contained in a class inheriting from <i> TDocStd_Application</i>
2666 which manages creation, storage and retrieval of documents.
2668 You can implement undo and redo in your document, and refer from the data framework
2669 of one document to that of another one. This is done by means of external link attributes,
2670 which store the path and the entry of external links. To sum up, standard documents
2671 alone provide access to the data framework. They also allow you to:
2672 *Update external links;
2673 *Manage the saving and opening of data;
2674 *Manage undo/redo functionality.
2676 @section OCCT_TOVW_SECTION_8 FAQ
2678 @subsection OCCT_TOVW_SECTION_8_1 Memory Management
2680 In a work-session, geometry modeling applications create and delete a certain number
2681 of C++ objects. In this context, memory allocation and de-allocation standard functions
2682 are not suited to the system's requirements and for this reason a specialized Memory
2683 Manager is implemented into Open CASCADE Technology. The Memory Manager is based
2684 on the following principles:
2686 * small memory arrays are grouped into clusters and then recycled (clusters are never released to the system),
2687 * large arrays are allocated and de-allocated through the standard functions of the system (the arrays are released to system when they are no longer used).
2689 ### The Reference Counter
2691 To lighten usual programming difficulties linked to the management of object life duration, before deleting an object, the user must ensure the object is no longer referenced and the delete function is secured by a reference counter.
2692 A smart-pointer called *Handle* automates reference counter management and automatically deletes an object when it is no longer referenced. The application never calls the delete operator explicitly. To benefit from the memory manager in OCCT, transient classes must inherit from <i>TShared</i>. The principle of allocation is as follows:
2695 Handle (TColStd_HSequenceOfInteger) H1 = new TColStd_HSequenceOfInteger;
2696 // H1 has one reference and corresponds to 48 bytes of memory
2698 Handle (TColStd_HSequenceOfInteger) H2;
2699 H2 = H1; // H1 has two references
2702 Handle (TColStd_HSequenceOfInteger) H3;
2704 // Here, H1 has three references
2706 // Here, H1 has two references
2708 // Here, H1 has 1 reference
2710 // Here, H1 has no reference but the 48 bytes of memory are kept.
2711 Handle (TColStd_HSequenceOfInteger) H1 = new TColStd_HSequenceOfInteger;
2712 // Here, H1 has one reference and corresponds to the preceding 48 bytes of
2713 // memory. In this case, there is no allocation of memory.
2718 As cycles are objects which reference one another, memory management is impossible if the data structure contains any cycles, particularly if there are back references.
2720 For example, objects in a graph include primitives and each one of these primitives has to know the graphic object to which it belongs (i.e. a reference to this graphic object). With normal references, the classical handle is used. With back references, a pointer is used.
2722 ### Memory Consumption
2725 As a general rule, it is advisable to allocate memory through significant blocks.
2726 In this way, the user can work with blocks of contiguous data and it facilitates memory page manager processing.
2728 @subsection OCCT_TOVW_SECTION_8_2 How to define a handled object without CDL
2730 You can create a class manipulated by handle even if you do not use CDL (Open CASCADE Definition Language).
2731 To do that you have to use the <i>Define_Standard_Handle</i> macro which is defined in the include file <i> Standard_DefineHandle.hxx</i>.
2733 Here is an example which shows how to define a class <i> SamplePoint </i> manipulated by handle.
2740 #ifndef _Sample_Point_HeaderFile
2741 #define _Sample_Point_HeaderFile
2742 #ifndef _Standard_Macro_HeaderFile
2743 #include <Standard_Macro.hxx>
2745 #include <MMgt_TShared.hxx>
2746 #include <Standard_DefineHandle.hxx>
2747 // Handle definition
2750 DEFINE_STANDARD_HANDLE(Sample_Point,MMgt_TShared)
2751 class Sample_Point: public MMgt_TShared {
2754 Sample_Point(const Standard_Real, const
2756 void SetX(const Standard_Real x) {
2759 void SetY(const Standard_Real y) {
2762 Standard_Real X() const {
2765 Standard_Real Y() const {
2768 // some methods like DynamicType() or
2771 DEFINE_STANDARD_RTTI(Sample_Point)
2785 #include <Sample_Point.hxx>
2787 // Implementation of Handle and type mgt
2789 IMPLEMENT_STANDARD_HANDLE(Sample_Point,MMgt_TShared)
2790 IMPLEMENT_STANDARD_RTTI(Sample_Point,MMgt_TShared)
2792 // For ancestors, we add a IMPLEMENT_STANDARD_SUPERTYPE and
2793 // a IMPLEMENT_STANDARD_SUPERTYPE_ARRAY_ENTRY macro.
2794 // We must respect the order: from the direct ancestor class to the base class.
2796 IMPLEMENT_STANDARD_TYPE(Sample_Point)
2797 IMPLEMENT_STANDARD_SUPERTYPE(MMgt_TShared)
2798 IMPLEMENT_STANDARD_SUPERTYPE(Standard_Transient)
2799 IMPLEMENT_STANDARD_SUPERTYPE_ARRAY()
2800 IMPLEMENT_STANDARD_SUPERTYPE_ARRAY_ENTRY(MMgt_TShared)
2801 IMPLEMENT_STANDARD_SUPERTYPE_ARRAY_ENTRY(Standard_Transient)
2802 IMPLEMENT_STANDARD_SUPERTYPE_ARRAY_END()
2803 IMPLEMENT_STANDARD_TYPE_END(Sample_Point)
2805 // Constructors implementation
2807 Sample_Point::Sample_Point(const
2808 Standard_Real x, const Standard_Real y)
2813 Sample_Point::Sample_Point()
2820 @subsection OCCT_TOVW_SECTION_8_3 When is it necessary to use a handle?
2822 When designing an object, the user is faced with the choice of manipulating that
2823 object by value, or by handle.
2825 * If your object may have a long lifetime within the application and you want to make multiple references to it, it would be preferable to manipulate this object with a handle. The memory for the object will be allocated on the heap. The handle which points to that memory is a light object which can be rapidly passed in argument. This avoids the penalty of copying a large object.
2826 * If your object will have a limited lifetime, for example, used within a single algorithm, it would be preferable to manipulate this object by value, non-regarding its size, because this object is allocated on the stack and the allocation and de-allocation of memory is extremely rapid, which avoids the implicit calls to 'new' and 'delete' occasioned by allocation on the heap.
2827 * Finally, if an object will be created only once during, but will exist throughout the lifetime of the application, the best choice may be a class manipulated by handle or a value declared as a global variable.
2830 @subsection OCCT_TOVW_SECTION_8_4 How to cast shape handle to void
2832 You can easily cast a reference to the handle object to <i> void* </i> by defining the following:
2836 Handle(Some_class) aHandle;
2837 // Here only a pointer will be copied
2839 // Here the Handle object will be copied
2840 aHandle = * (Handle(Some_Class) *)pointer;
2843 @subsection OCCT_TOVW_SECTION_8_5 How to test correct ending of OCCT algorithms
2845 Generally OCCT algorithms implement <i> IsDone</i> method, which returns <i> true</i>
2846 if computation has been performed successfully from beginning to end or <i> false</i> if computation has failed.
2848 When <i> IsDone</i> returns <i> true</i>, the computation is successful regarding
2849 to the input data, but it does not necessary mean that you get a result. For example, if
2850 you perform a cut algorithm between two shapes without any common part, the <i> IsDone</i>
2851 method will return <i> true</i>, but the result will be empty.
2853 So, in some cases, it can be necessary to analyse the structure of a result before
2854 using it again in following computations. These tests are not done systematically
2855 into algorithms to get faster computations. The application performs necessary tests
2856 depending on the context.
2858 @subsection OCCT_TOVW_SECTION_8_6 How to cut, copy and paste inside a document
2860 To cut, copy and paste inside a document, you must use the <i> CopyLabel</i> class from the <i> TDF</i> package.
2861 In fact, you must define a Label which contains the temporary value a cut or
2862 copy operation (say, in <i> Lab_Clipboard</i>). You must also define two other labels:
2864 * One containing the data (e.g. <i> Lab_source</i>)
2865 * One for the destination of the copy (e.g. <i> Lab_ Target</i> )
2868 Copy = copy (Lab_Source => Lab_Clipboard)
2869 Cut = copy + Lab_Source.ForgetAll() // command clear the contents of LabelSource.
2870 Paste = copy (Lab_Clipboard => Lab_target)
2873 So we need a tool to copy all (or a part) of the content of a label and its sub-label,
2874 to another place defined by a label.
2877 TDF_CopyLabel aCopy;
2878 TDF_IDFilter aFilter (Standard_False);
2880 //Don't copy TDataStd_TreeNode attribute
2882 aFilter.Ignore(TDataStd_TreeNode::GetDefaultTreeID());
2883 aCopy.Load(aSource, aTarget); aCopy.UseFilter(aFilter); aCopy.Perform();
2885 // copy the data structure to clipboard
2887 return aCopy.IsDone(); }
2890 The filter is used to forbid copying a specified type of attribute.
2891 You can also have a look at *TDF_Closure**,
2892 which can be useful to determine the dependencies of the part you want to cut from the document.
2894 @subsection OCCT_TOVW_SECTION_8_7 Platform-related problems
2896 ### Dynamic library loading
2898 Open CASCADE Technology uses a dynamic library loading mode. Sometimes, the error message such as the following appears:
2901 "cannot map libname.so .. under any of the filenames .."
2904 When this happens, check your *PATH* under Windows, *LD_LIBRARY_PATH* under UNIX ,
2905 *SHLIB_PATH* under HP-UX or *LIBPATH* under IBM AIX .
2906 It should contain the path where the required dynamic library is located.
2908 ### Running Draw under Windows
2911 When running <i> DRAWEXE</i> and using axo in the Command window you may see the "Invalid command name "axo" " message :
2913 Make sure that the OCCT directory name does not contain any blank spaces.
2914 It causes some problems when reading the OCCT description TCL Commands files.
2915 If you have set <i> DRAWHOME</i> and <i> DRAWDEFAULT</i>, replace \\ by / in the variable.
2917 ### Error on application start on Windows
2919 If Windows shows an error message with the text *Application failed to initialize properly*
2920 upon launching the application, check access rights for all libraries used in the application, in particular, third-party libraries.
2922 Make sure that you have all rights necessary to access these libraries.
2923 It is recommended to use option *Inherit access rights from parent*.
2925 ### Problems with 3D viewer
2928 If the 3D viewer fails to display the scene properly, or works very slowly, or exhibits
2929 another problem, make sure to have the latest version of the graphics card driver
2930 installed. If this is not possible or does not help, try to decrease
2931 hardware acceleration level (usually found in Troubleshooting section of the graphics card properties).