9 This tutorial will teach you how to use Open CASCADE Technology services to model a 3D object. The purpose of this tutorial is not to describe all Open CASCADE Technology classes but to help you start thinking in terms of Open CASCADE Technology as a tool.
12 @subsection OCCT_TUTORIAL_SUB1_1 Prerequisites
14 This tutorial assumes that you have experience in using and setting up C++.
15 From a programming standpoint, Open CASCADE Technology is designed to enhance your C++ tools with 3D modeling classes, methods and functions. The combination of all these resources will allow you to create substantial applications.
17 @subsection OCCT_TUTORIAL_SUB1_2 The Model
19 To illustrate the use of classes provided in the 3D geometric modeling toolkits, you will create a bottle as shown:
21 @image html /tutorial/images/tutorial_image001.png
22 @image latex /tutorial/images/tutorial_image001.png
24 In the tutorial we will create, step-by-step, a function that will model a bottle as shown above. You will find the complete source code of this tutorial, including the very function *MakeBottle* in the distribution of Open CASCADE Technology. The function body is provided in the file samples/qt/Tutorial/src/MakeBottle.cxx.
26 @subsection OCCT_TUTORIAL_SUB1_3 Model Specifications
28 We first define the bottle specifications as follows:
30 | Object Parameter | Parameter Name | Parameter Value |
31 | :--------------: | :------------: | :-------------: |
32 | Bottle height | MyHeight | 70mm |
33 | Bottle width | MyWidth | 50mm |
34 | Bottle thickness | MyThickness | 30mm |
36 In addition, we decide that the bottle's profile (base) will be centered on the origin of the global Cartesian coordinate system.
38 @image html /tutorial/images/tutorial_image002.png
39 @image latex /tutorial/images/tutorial_image002.png
41 This modeling requires four steps:
43 * build the bottle's Profile
44 * build the bottle's Body
45 * build the Threading on the bottle's neck
46 * build the result compound
49 @section sec2 Building the Profile
51 @subsection OCCT_TUTORIAL_SUB2_1 Defining Support Points
53 To create the bottle's profile, you first create characteristic points with their coordinates as shown below in the (XOY) plane. These points will be the supports that define the geometry of the profile.
55 @figure{/tutorial/images/tutorial_image003.svg}
57 There are two classes to describe a 3D Cartesian point from its X, Y and Z coordinates in Open CASCADE Technology:
59 * the primitive geometric *gp_Pnt* class
60 * the transient *Geom_CartesianPoint* class manipulated by handle
62 A handle is a type of smart pointer that provides automatic memory management.
63 To choose the best class for this application, consider the following:
65 * *gp_Pnt* is manipulated by value. Like all objects of its kind, it will have a limited lifetime.
66 * *Geom_CartesianPoint* is manipulated by handle and may have multiple references and a long lifetime.
68 Since all the points you will define are only used to create the profile's curves, an object with a limited lifetime will do. Choose the *gp_Pnt* class.
69 To instantiate a *gp_Pnt* object, just specify the X, Y, and Z coordinates of the points in the global Cartesian coordinate system:
71 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
72 gp_Pnt aPnt1(-myWidth / 2., 0, 0);
73 gp_Pnt aPnt2(-myWidth / 2., -myThickness / 4., 0);
74 gp_Pnt aPnt3(0, -myThickness / 2., 0);
75 gp_Pnt aPnt4(myWidth / 2., -myThickness / 4., 0);
76 gp_Pnt aPnt5(myWidth / 2., 0, 0);
77 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
79 Once your objects are instantiated, you can use methods provided by the class to access and modify its data. For example, to get the X coordinate of a point:
81 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
82 Standard_Real xValue1 = aPnt1.X();
83 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
85 @subsection OCCT_TUTORIAL_SUB2_2 Profile: Defining the Geometry
86 With the help of the previously defined points, you can compute a part of the bottle's profile geometry. As shown in the figure below, it will consist of two segments and one arc.
88 @image html /tutorial/images/tutorial_image004.png
89 @image latex /tutorial/images/tutorial_image004.png
91 To create such entities, you need a specific data structure, which implements 3D geometric objects. This can be found in the Geom package of Open CASCADE Technology.
92 In Open CASCADE Technology a package is a group of classes providing related functionality. The classes have names that start with the name of a package they belong to. For example, *Geom_Line* and *Geom_Circle* classes belong to the *Geom* package. The *Geom* package implements 3D geometric objects: elementary curves and surfaces are provided as well as more complex ones (such as *Bezier* and *BSpline*).
93 However, the *Geom* package provides only the data structure of geometric entities. You can directly instantiate classes belonging to *Geom*, but it is easier to compute elementary curves and surfaces by using the *GC* package.
94 This is because the *GC* provides two algorithm classes which are exactly what is required for our profile:
96 * Class *GC_MakeSegment* to create a segment. One of its constructors allows you to define a segment by two end points P1 and P2
97 * Class *GC_MakeArcOfCircle* to create an arc of a circle. A useful constructor creates an arc from two end points P1 and P3 and going through P2.
99 Both of these classes return a *Geom_TrimmedCurve* manipulated by handle. This entity represents a base curve (line or circle, in our case), limited between two of its parameter values. For example, circle C is parameterized between 0 and 2PI. If you need to create a quarter of a circle, you create a *Geom_TrimmedCurve* on C limited between 0 and M_PI/2.
101 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
102 Handle(Geom_TrimmedCurve) aArcOfCircle = GC_MakeArcOfCircle(aPnt2,aPnt3,aPnt4);
103 Handle(Geom_TrimmedCurve) aSegment1 = GC_MakeSegment(aPnt1, aPnt2);
104 Handle(Geom_TrimmedCurve) aSegment2 = GC_MakeSegment(aPnt4, aPnt5);
105 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
107 All *GC* classes provide a casting method to obtain a result automatically with a function-like call. Note that this method will raise an exception if construction has failed. To handle possible errors more explicitly, you may use the *IsDone* and *Value* methods. For example:
109 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
110 GC_MakeSegment mkSeg (aPnt1, aPnt2);
111 Handle(Geom_TrimmedCurve) aSegment1;
112 if(mkSegment.IsDone()){
113 aSegment1 = mkSeg.Value();
118 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
121 @subsection OCCT_TUTORIAL_SUB2_3 Profile: Defining the Topology
124 You have created the support geometry of one part of the profile but these curves are independent with no relations between each other.
125 To simplify the modeling, it would be right to manipulate these three curves as a single entity.
126 This can be done by using the topological data structure of Open CASCADE Technology defined in the *TopoDS* package: it defines relationships between geometric entities which can be linked together to represent complex shapes.
127 Each object of the *TopoDS* package, inheriting from the *TopoDS_Shape* class, describes a topological shape as described below:
129 | Shape | Open CASCADE Technology Class | Description |
130 | :-------- | :---------------------------- | :------------------------------------------------------------ |
131 | Vertex | TopoDS_Vertex | Zero dimensional shape corresponding to a point in geometry. |
132 | Edge | TopoDS_Edge | One-dimensional shape corresponding to a curve and bounded by a vertex at each extremity.|
133 | Wire | TopoDS_Wire | Sequence of edges connected by vertices. |
134 | Face | TopoDS_Face | Part of a surface bounded by a closed wire(s). |
135 | Shell | TopoDS_Shell | Set of faces connected by edges. |
136 | Solid | TopoDS_Solid | Part of 3D space bounded by Shells. |
137 | CompSolid | TopoDS_CompSolid | Set of solids connected by their faces. |
138 | Compound | TopoDS_Compound | Set of any other shapes described above. |
140 Referring to the previous table, to build the profile, you will create:
142 * Three edges out of the previously computed curves.
143 * One wire with these edges.
145 @image html /tutorial/images/tutorial_image005.png
146 @image latex /tutorial/images/tutorial_image005.png
148 However, the *TopoDS* package provides only the data structure of the topological entities. Algorithm classes available to compute standard topological objects can be found in the *BRepBuilderAPI* package.
149 To create an edge, you use the BRepBuilderAPI_MakeEdge class with the previously computed curves:
151 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
152 TopoDS_Edge aEdge1 = BRepBuilderAPI_MakeEdge(aSegment1);
153 TopoDS_Edge aEdge2 = BRepBuilderAPI_MakeEdge(aArcOfCircle);
154 TopoDS_Edge aEdge3 = BRepBuilderAPI_MakeEdge(aSegment2);
155 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
157 In Open CASCADE Technology, you can create edges in several ways. One possibility is to create an edge directly from two points, in which case the underlying geometry of this edge is a line, bounded by two vertices being automatically computed from the two input points. For example, aEdge1 and aEdge3 could have been computed in a simpler way:
159 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
160 TopoDS_Edge aEdge1 = BRepBuilderAPI_MakeEdge(aPnt1, aPnt3);
161 TopoDS_Edge aEdge2 = BRepBuilderAPI_MakeEdge(aPnt4, aPnt5);
162 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
164 To connect the edges, you need to create a wire with the *BRepBuilderAPI_MakeWire* class. There are two ways of building a wire with this class:
166 * directly from one to four edges
167 * by adding other wire(s) or edge(s) to an existing wire (this is explained later in this tutorial)
169 When building a wire from less than four edges, as in the present case, you can use the constructor directly as follows:
171 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
172 TopoDS_Wire aWire = BRepBuilderAPI_MakeWire(aEdge1, aEdge2, aEdge3);
173 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
176 @subsection OCCT_TUTORIAL_SUB2_4 Profile: Completing the Profile
179 Once the first part of your wire is created you need to compute the complete profile. A simple way to do this is to:
181 * compute a new wire by reflecting the existing one.
182 * add the reflected wire to the initial one.
184 @image html /tutorial/images/tutorial_image006.png
185 @image latex /tutorial/images/tutorial_image006.png
187 To apply a transformation on shapes (including wires), you first need to define the properties of a 3D geometric transformation by using the gp_Trsf class. This transformation can be a translation, a rotation, a scale, a reflection, or a combination of these.
188 In our case, we need to define a reflection with respect to the X axis of the global coordinate system. An axis, defined with the gp_Ax1 class, is built out of a point and has a direction (3D unitary vector). There are two ways to define this axis.
189 The first way is to define it from scratch, using its geometric definition:
191 * X axis is located at (0, 0, 0) - use the *gp_Pnt* class.
192 * X axis direction is (1, 0, 0) - use the *gp_Dir* class. A *gp_Dir* instance is created out of its X, Y and Z coordinates.
194 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
195 gp_Pnt aOrigin(0, 0, 0);
196 gp_Dir xDir(1, 0, 0);
197 gp_Ax1 xAxis(aOrigin, xDir);
198 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
200 The second and simplest way is to use the geometric constants defined in the gp package (origin, main directions and axis of the global coordinate system). To get the X axis, just call the *gp::OX* method:
202 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
203 gp_Ax1 xAxis = gp::OX();
204 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
206 As previously explained, the 3D geometric transformation is defined with the *gp_Trsf* class. There are two different ways to use this class:
208 * by defining a transformation matrix by all its values
209 * by using the appropriate methods corresponding to the required transformation (SetTranslation for a translation, SetMirror for a reflection, etc.): the matrix is automatically computed.
211 Since the simplest approach is always the best one, you should use the SetMirror method with the axis as the center of symmetry.
213 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
215 aTrsf.SetMirror(xAxis);
216 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
218 You now have all necessary data to apply the transformation with the BRepBuilderAPI_Transform class by specifying:
220 * the shape on which the transformation must be applied.
221 * the geometric transformation
223 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
224 BRepBuilderAPI_Transform aBRepTrsf(aWire, aTrsf);
225 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
227 *BRepBuilderAPI_Transform* does not modify the nature of the shape: the result of the reflected wire remains a wire. But the function-like call or the *BRepBuilderAPI_Transform::Shape* method returns a *TopoDS_Shape* object:
229 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
230 TopoDS_Shape aMirroredShape = aBRepTrsf.Shape();
231 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
233 What you need is a method to consider the resulting reflected shape as a wire. The *TopoDS* global functions provide this kind of service by casting a shape into its real type. To cast the transformed wire, use the *TopoDS::Wire* method.
235 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
236 TopoDS_Wire aMirroredWire = TopoDS::Wire(aMirroredShape);
237 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
239 The bottle's profile is almost finished. You have created two wires: *aWire* and *aMirroredWire*. You need to concatenate them to compute a single shape. To do this, you use the *BRepBuilderAPI_MakeWire* class as follows:
241 * create an instance of *BRepBuilderAPI_MakeWire*.
242 * add all edges of the two wires by using the *Add* method on this object.
244 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
245 BRepBuilderAPI_MakeWire mkWire;
247 mkWire.Add(aMirroredWire);
248 TopoDS_Wire myWireProfile = mkWire.Wire();
249 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
252 @section sec3 Building the Body
255 @subsection OCCT_TUTORIAL_SUB3_1 Prism the Profile
258 To compute the main body of the bottle, you need to create a solid shape. The simplest way is to use the previously created profile and to sweep it along a direction. The *Prism* functionality of Open CASCADE Technology is the most appropriate for that task. It accepts a shape and a direction as input and generates a new shape according to the following rules:
260 | Shape | Generates |
261 | :----- | :----------------- |
266 | Shell | Compound of Solids |
268 @image html /tutorial/images/tutorial_image007.png
269 @image latex /tutorial/images/tutorial_image007.png
271 Your current profile is a wire. Referring to the Shape/Generates table, you need to compute a face out of its wire to generate a solid.
272 To create a face, use the *BRepBuilderAPI_MakeFace* class. As previously explained, a face is a part of a surface bounded by a closed wire. Generally, *BRepBuilderAPI_MakeFace* computes a face out of a surface and one or more wires.
273 When the wire lies on a plane, the surface is automatically computed.
275 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
276 TopoDS_Face myFaceProfile = BRepBuilderAPI_MakeFace(myWireProfile);
277 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
279 The *BRepPrimAPI* package provides all the classes to create topological primitive constructions: boxes, cones, cylinders, spheres, etc. Among them is the *BRepPrimAPI_MakePrism* class. As specified above, the prism is defined by:
281 * the basis shape to sweep;
282 * a vector for a finite prism or a direction for finite and infinite prisms.
284 You want the solid to be finite, swept along the Z axis and to be myHeight height. The vector, defined with the *gp_Vec* class on its X, Y and Z coordinates, is:
286 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
287 gp_Vec aPrismVec(0, 0, myHeight);
288 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
290 All the necessary data to create the main body of your bottle is now available. Just apply the *BRepPrimAPI_MakePrism* class to compute the solid:
292 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
293 TopoDS_Shape myBody = BRepPrimAPI_MakePrism(myFaceProfile, aPrismVec);
294 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
297 @subsection OCCT_TUTORIAL_SUB3_2 Applying Fillets
300 The edges of the bottle's body are very sharp. To replace them by rounded faces, you use the *Fillet* functionality of Open CASCADE Technology.
301 For our purposes, we will specify that fillets must be:
303 * applied on all edges of the shape
304 * have a radius of *myThickness* / 12
306 @image html /tutorial/images/tutorial_image008.png
307 @image latex /tutorial/images/tutorial_image008.png
309 To apply fillets on the edges of a shape, you use the *BRepFilletAPI_MakeFillet* class. This class is normally used as follows:
311 * Specify the shape to be filleted in the *BRepFilletAPI_MakeFillet* constructor.
312 * Add the fillet descriptions (an edge and a radius) using the *Add* method (you can add as many edges as you need).
313 * Ask for the resulting filleted shape with the *Shape* method.
315 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
316 BRepFilletAPI_MakeFillet mkFillet(myBody);
317 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
319 To add the fillet description, you need to know the edges belonging to your shape. The best solution is to explore your solid to retrieve its edges. This kind of functionality is provided with the *TopExp_Explorer* class, which explores the data structure described in a *TopoDS_Shape* and extracts the sub-shapes you specifically need.
320 Generally, this explorer is created by providing the following information:
322 * the shape to explore
323 * the type of sub-shapes to be found. This information is given with the *TopAbs_ShapeEnum* enumeration.
325 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
326 TopExp_Explorer anEdgeExplorer(myBody, TopAbs_EDGE);
327 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
329 An explorer is usually applied in a loop by using its three main methods:
331 * *More()* to know if there are more sub-shapes to explore.
332 * *Current()* to know which is the currently explored sub-shape (used only if the *More()* method returns true).
333 * *Next()* to move onto the next sub-shape to explore.
336 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
337 while(anEdgeExplorer.More()){
338 TopoDS_Edge anEdge = TopoDS::Edge(anEdgeExplorer.Current());
339 //Add edge to fillet algorithm
341 anEdgeExplorer.Next();
343 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
345 In the explorer loop, you have found all the edges of the bottle shape. Each one must then be added in the *BRepFilletAPI_MakeFillet* instance with the *Add()* method. Do not forget to specify the radius of the fillet along with it.
347 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
348 mkFillet.Add(myThickness / 12., anEdge);
349 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
351 Once this is done, you perform the last step of the procedure by asking for the filleted shape.
353 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
354 myBody = mkFillet.Shape();
355 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
358 @subsection OCCT_TUTORIAL_SUB3_3 Adding the Neck
361 To add a neck to the bottle, you will create a cylinder and fuse it to the body. The cylinder is to be positioned on the top face of the body with a radius of *myThickness* / 4. and a height of *myHeight* / 10.
363 @image html /tutorial/images/tutorial_image009.png
364 @image latex /tutorial/images/tutorial_image009.png
366 To position the cylinder, you need to define a coordinate system with the *gp_Ax2* class defining a right-handed coordinate system from a point and two directions - the main (Z) axis direction and the X direction (the Y direction is computed from these two).
367 To align the neck with the center of the top face, being in the global coordinate system (0, 0, *myHeight*), with its normal on the global Z axis, your local coordinate system can be defined as follows:
369 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
370 gp_Pnt neckLocation(0, 0, myHeight);
371 gp_Dir neckAxis = gp::DZ();
372 gp_Ax2 neckAx2(neckLocation, neckAxis);
373 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
375 To create a cylinder, use another class from the primitives construction package: the *BRepPrimAPI_MakeCylinder* class. The information you must provide is:
377 * the coordinate system where the cylinder will be located;
378 * the radius and height.
380 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
381 Standard_Real myNeckRadius = myThickness / 4.;
382 Standard_Real myNeckHeight = myHeight / 10;
383 BRepPrimAPI_MakeCylinder MKCylinder(neckAx2, myNeckRadius, myNeckHeight);
384 TopoDS_Shape myNeck = MKCylinder.Shape();
385 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
387 You now have two separate parts: a main body and a neck that you need to fuse together.
388 The *BRepAlgoAPI* package provides services to perform Boolean operations between shapes, and especially: *common* (Boolean intersection), *cut* (Boolean subtraction) and *fuse* (Boolean union).
389 Use *BRepAlgoAPI_Fuse* to fuse the two shapes:
391 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
392 myBody = BRepAlgoAPI_Fuse(myBody, myNeck);
393 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
396 @subsection OCCT_TUTORIAL_SUB3_4 Creating a Hollowed Solid
399 Since a real bottle is used to contain liquid material, you should now create a hollowed solid from the bottle's top face.
400 In Open CASCADE Technology, a hollowed solid is called a *Thick* *Solid* and is internally computed as follows:
402 * Remove one or more faces from the initial solid to obtain the first wall W1 of the hollowed solid.
403 * Create a parallel wall W2 from W1 at a distance D. If D is positive, W2 will be outside the initial solid, otherwise it will be inside.
404 * Compute a solid from the two walls W1 and W2.
406 @image html /tutorial/images/tutorial_image010.png
407 @image latex /tutorial/images/tutorial_image010.png
409 To compute a thick solid, you create an instance of the *BRepOffsetAPI_MakeThickSolid* class by giving the following information:
411 * The shape, which must be hollowed.
412 * The tolerance used for the computation (tolerance criterion for coincidence in generated shapes).
413 * The thickness between the two walls W1 and W2 (distance D).
414 * The face(s) to be removed from the original solid to compute the first wall W1.
416 The challenging part in this procedure is to find the face to remove from your shape - the top face of the neck, which:
418 * has a plane (planar surface) as underlying geometry;
419 * is the highest face (in Z coordinates) of the bottle.
421 To find the face with such characteristics, you will once again use an explorer to iterate on all the bottle's faces to find the appropriate one.
423 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
424 for(TopExp_Explorer aFaceExplorer(myBody, TopAbs_FACE) ; aFaceExplorer.More() ; aFaceExplorer.Next()){
425 TopoDS_Face aFace = TopoDS::Face(aFaceExplorer.Current());
427 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
429 For each detected face, you need to access the geometric properties of the shape: use the *BRep_Tool* class for that. The most commonly used methods of this class are:
431 * *Surface* to access the surface of a face;
432 * *Curve* to access the 3D curve of an edge;
433 * *Point* to access the 3D point of a vertex.
435 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
436 Handle(Geom_Surface) aSurface = BRep_Tool::Surface(aFace);
437 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
439 As you can see, the *BRep_Tool::Surface* method returns an instance of the *Geom_Surface* class manipulated by handle. However, the *Geom_Surface* class does not provide information about the real type of the object *aSurface*, which could be an instance of *Geom_Plane*, *Geom_CylindricalSurface*, etc.
440 All objects manipulated by handle, like *Geom_Surface*, inherit from the *Standard_Transient* class which provides two very useful methods concerning types:
442 * *DynamicType* to know the real type of the object
443 * *IsKind* to know if the object inherits from one particular type
445 DynamicType returns the real type of the object, but you need to compare it with the existing known types to determine whether *aSurface* is a plane, a cylindrical surface or some other type.
446 To compare a given type with the type you seek, use the *STANDARD_TYPE* macro, which returns the type of a class:
448 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
449 if(aSurface->DynamicType() == STANDARD_TYPE(Geom_Plane)){
452 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
454 If this comparison is true, you know that the *aSurface* real type is *Geom_Plane*. You can then convert it from *Geom_Surface* to *Geom_Plane* by using the *DownCast()* method provided by each class inheriting *Standard_Transient*. As its name implies, this static method is used to downcast objects to a given type with the following syntax:
456 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
457 Handle(Geom_Plane) aPlane = Handle(Geom_Plane)::DownCast(aSurface);
458 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
460 Remember that the goal of all these conversions is to find the highest face of the bottle lying on a plane. Suppose that you have these two global variables:
462 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
463 TopoDS_Face faceToRemove;
464 Standard_Real zMax = -1;
465 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
467 You can easily find the plane whose origin is the biggest in Z knowing that the location of the plane is given with the *Geom_Plane::Location* method. For example:
469 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
470 gp_Pnt aPnt = aPlane->Location();
471 Standard_Real aZ = aPnt.Z();
474 faceToRemove = aFace;
476 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
478 You have now found the top face of the neck. Your final step before creating the hollowed solid is to put this face in a list. Since more than one face can be removed from the initial solid, the *BRepOffsetAPI_MakeThickSolid* constructor takes a list of faces as arguments.
479 Open CASCADE Technology provides many collections for different kinds of objects: see *TColGeom* package for collections of objects from *Geom* package, *TColgp* package for collections of objects from gp package, etc.
480 The collection for shapes can be found in the *TopTools* package. As *BRepOffsetAPI_MakeThickSolid* requires a list, use the *TopTools_ListOfShape* class.
482 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
483 TopTools_ListOfShape facesToRemove;
484 facesToRemove.Append(faceToRemove);
485 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
487 All the necessary data are now available so you can create your hollowed solid by calling the *BRepOffsetAPI_MakeThickSolid* constructor:
489 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
490 MyBody = BRepOffsetAPI_MakeThickSolid(myBody, facesToRemove, -myThickness / 50, 1.e-3);
491 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
494 @section sec4 Building the Threading
497 @subsection OCCT_TUTORIAL_SUB4_1 Creating Surfaces
500 Up to now, you have learned how to create edges out of 3D curves.
501 You will now learn how to create an edge out of a 2D curve and a surface.
502 To learn this aspect of Open CASCADE Technology, you will build helicoidal profiles out of 2D curves on cylindrical surfaces. The theory is more complex than in previous steps, but applying it is very simple.
503 As a first step, you compute these cylindrical surfaces. You are already familiar with curves of the *Geom* package. Now you can create a cylindrical surface (*Geom_CylindricalSurface*) using:
505 * a coordinate system;
508 Using the same coordinate system *neckAx2* used to position the neck, you create two cylindrical surfaces *Geom_CylindricalSurface* with the following radii:
510 @image html /tutorial/images/tutorial_image011.png
511 @image latex /tutorial/images/tutorial_image011.png
513 Notice that one of the cylindrical surfaces is smaller than the neck. There is a good reason for this: after the thread creation, you will fuse it with the neck. So, we must make sure that the two shapes remain in contact.
515 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
516 Handle(Geom_CylindricalSurface) aCyl1 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 0.99);
518 Handle(Geom_CylindricalSurface) aCyl2 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 1.05);
519 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
522 @subsection OCCT_TUTORIAL_SUB4_2 Defining 2D Curves
525 To create the neck of the bottle, you made a solid cylinder based on a cylindrical surface. You will create the profile of threading by creating 2D curves on such a surface.
526 All geometries defined in the *Geom* package are parameterized. This means that each curve or surface from Geom is computed with a parametric equation.
527 A *Geom_CylindricalSurface* surface is defined with the following parametric equation:
529 P(U, V) = O + R * (cos(U) * xDir + sin(U) * yDir) + V * zDir, where :
531 * P is the point defined by parameters (U, V).
532 * O, *Dir, yDir and zDir are respectively the origin, the X direction, Y direction and Z direction of the cylindrical surface local coordinate system.
533 * R is the radius of the cylindrical surface.
534 * U range is [0, 2PI] and V is infinite.
536 @image html /tutorial/images/tutorial_image012.png
537 @image latex /tutorial/images/tutorial_image012.png
539 The advantage of having such parameterized geometries is that you can compute, for any (U, V) parameters of the surface:
542 * the derivative vectors of order 1, 2 to N at this point.
544 There is another advantage of these parametric equations: you can consider a surface as a 2D parametric space defined with a (U, V) coordinate system. For example, consider the parametric ranges of the neck's surface:
546 @image html /tutorial/images/tutorial_image013.png
547 @image latex /tutorial/images/tutorial_image013.png
549 Suppose that you create a 2D line on this parametric (U, V) space and compute its 3D parametric curve. Depending on the line definition, results are as follows:
551 | Case | Parametric Equation | Parametric Curve |
552 | :------------ | :----------------------------------------------------------- | :---------------------------------------------------------------------------- |
553 | U = 0 | P(V) = O + V * zDir | Line parallel to the Z direction |
554 | V = 0 | P(U) = O + R * (cos(U) * xDir + sin(U) * yDir) | Circle parallel to the (O, X, Y) plane |
555 | U != 0 V != 0 | P(U, V) = O + R * (cos(U) * xDir + sin(U) * yDir) + V * zDir | Helicoidal curve describing the evolution of height and angle on the cylinder |
557 The helicoidal curve type is exactly what you need. On the neck's surface, the evolution laws of this curve will be:
559 * In V parameter: between 0 and myHeighNeck for the height description
560 * In U parameter: between 0 and 2PI for the angle description. But, since a cylindrical surface is U periodic, you can decide to extend this angle evolution to 4PI as shown in the following drawing:
562 @image html /tutorial/images/tutorial_image014.png
563 @image latex /tutorial/images/tutorial_image014.png
565 In this (U, V) parametric space, you will create a local (X, Y) coordinate system to position the curves to be created. This coordinate system will be defined with:
567 * A center located in the middle of the neck's cylinder parametric space at (2*PI, myNeckHeight / 2) in U, V coordinates.
568 * A X direction defined with the (2*PI, myNeckHeight/4) vector in U, V coordinates, so that the curves occupy half of the neck's surfaces.
570 @image html /tutorial/images/tutorial_image015.png
571 @image latex /tutorial/images/tutorial_image015.png
573 To use 2D primitive geometry types of Open CASCADE Technology for defining a point and a coordinate system, you will once again instantiate classes from gp:
575 * To define a 2D point from its X and Y coordinates, use the *gp_Pnt2d* class.
576 * To define a 2D direction (unit vector) from its X and Y coordinates, use the gp_Dir2d class. The coordinates will automatically be normalized.
577 * To define a 2D right-handed coordinate system, use the *gp_Ax2d* class, which is computed from a point (origin of the coordinate system) and a direction - the X direction of the coordinate system. The Y direction will be automatically computed.
579 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
580 gp_Pnt2d aPnt(2. * M_PI, myNeckHeight / 2.);
581 gp_Dir2d aDir(2. * M_PI, myNeckHeight / 4.);
582 gp_Ax2d anAx2d(aPnt, aDir);
583 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
585 You will now define the curves. As previously mentioned, these thread profiles are computed on two cylindrical surfaces. In the following figure, curves on the left define the base (on *aCyl1* surface) and the curves on the right define the top of the thread's shape (on *aCyl2* surface).
587 @image html /tutorial/images/tutorial_image016.png
588 @image latex /tutorial/images/tutorial_image016.png
590 You have already used the *Geom* package to define 3D geometric entities. For 2D, you will use the *Geom2d* package. As for *Geom*, all geometries are parameterized. For example, a *Geom2d_Ellipse* ellipse is defined from:
592 * a coordinate system whose origin is the ellipse center;
593 * a major radius on the major axis defined by the X direction of the coordinate system;
594 * a minor radius on the minor axis defined by the Y direction of the coordinate system.
598 * Both ellipses have the same major radius of 2*PI,
599 * Minor radius of the first ellipse is myNeckHeight / 10,
600 * And the minor radius value of the second ellipse is a fourth of the first one,
602 Your ellipses are defined as follows:
604 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
605 Standard_Real aMajor = 2. * M_PI;
606 Standard_Real aMinor = myNeckHeight / 10;
607 Handle(Geom2d_Ellipse) anEllipse1 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor);
608 Handle(Geom2d_Ellipse) anEllipse2 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor / 4);
609 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
611 To describe portions of curves for the arcs drawn above, you define *Geom2d_TrimmedCurve* trimmed curves out of the created ellipses and two parameters to limit them.
612 As the parametric equation of an ellipse is P(U) = O + (MajorRadius * cos(U) * XDirection) + (MinorRadius * sin(U) * YDirection), the ellipses need to be limited between 0 and M_PI.
614 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
615 Handle(Geom2d_TrimmedCurve) anArc1 = new Geom2d_TrimmedCurve(anEllipse1, 0, M_PI);
616 Handle(Geom2d_TrimmedCurve) anArc2 = new Geom2d_TrimmedCurve(anEllipse2, 0, M_PI);
617 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
619 The last step consists in defining the segment, which is the same for the two profiles: a line limited by the first and the last point of one of the arcs.
620 To access the point corresponding to the parameter of a curve or a surface, you use the Value or D0 method (meaning 0th derivative), D1 method is for first derivative, D2 for the second one.
622 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
623 gp_Pnt2d anEllipsePnt1 = anEllipse1->Value(0);
624 gp_Pnt2d anEllipsePnt2;
625 anEllipse1->D0(M_PI, anEllipsePnt2);
626 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
628 When creating the bottle's profile, you used classes from the *GC* package, providing algorithms to create elementary geometries.
629 In 2D geometry, this kind of algorithms is found in the *GCE2d* package. Class names and behaviors are similar to those in *GC*. For example, to create a 2D segment out of two points:
631 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
632 Handle(Geom2d_TrimmedCurve) aSegment = GCE2d_MakeSegment(anEllipsePnt1, anEllipsePnt2);
633 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
636 @subsection OCCT_TUTORIAL_SUB4_3 Building Edges and Wires
639 As you did when creating the base profile of the bottle, you can now:
641 * compute the edges of the neck's threading.
642 * compute two wires out of these edges.
644 @image html /tutorial/images/tutorial_image017.png
645 @image latex /tutorial/images/tutorial_image017.png
647 Previously, you have built:
649 * two cylindrical surfaces of the threading
650 * three 2D curves defining the base geometry of the threading
652 To compute the edges out of these curves, once again use the *BRepBuilderAPI_MakeEdge* class. One of its constructors allows you to build an edge out of a curve described in the 2D parametric space of a surface.
654 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
655 TopoDS_Edge anEdge1OnSurf1 = BRepBuilderAPI_MakeEdge(anArc1, aCyl1);
656 TopoDS_Edge anEdge2OnSurf1 = BRepBuilderAPI_MakeEdge(aSegment, aCyl1);
657 TopoDS_Edge anEdge1OnSurf2 = BRepBuilderAPI_MakeEdge(anArc2, aCyl2);
658 TopoDS_Edge anEdge2OnSurf2 = BRepBuilderAPI_MakeEdge(aSegment, aCyl2);
659 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
661 Now, you can create the two profiles of the threading, lying on each surface.
663 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
664 TopoDS_Wire threadingWire1 = BRepBuilderAPI_MakeWire(anEdge1OnSurf1, anEdge2OnSurf1);
665 TopoDS_Wire threadingWire2 = BRepBuilderAPI_MakeWire(anEdge1OnSurf2, anEdge2OnSurf2);
666 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
668 Remember that these wires were built out of a surface and 2D curves.
669 One important data item is missing as far as these wires are concerned: there is no information on the 3D curves. Fortunately, you do not need to compute this yourself, which can be a difficult task since the mathematics can be quite complex.
670 When a shape contains all the necessary information except 3D curves, Open CASCADE Technology provides a tool to build them automatically. In the BRepLib tool package, you can use the *BuildCurves3d* method to compute 3D curves for all the edges of a shape.
672 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
673 BRepLib::BuildCurves3d(threadingWire1);
674 BRepLib::BuildCurves3d(threadingWire2);
675 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
678 @subsection OCCT_TUTORIAL_SUB4_4 Creating Threading
681 You have computed the wires of the threading. The threading will be a solid shape, so you must now compute the faces of the wires, the faces allowing you to join the wires, the shell out of these faces and then the solid itself. This can be a lengthy operation.
682 There are always faster ways to build a solid when the base topology is defined. You would like to create a solid out of two wires. Open CASCADE Technology provides a quick way to do this by building a loft: a shell or a solid passing through a set of wires in a given sequence.
683 The loft function is implemented in the *BRepOffsetAPI_ThruSections* class, which you use as follows:
685 @image html /tutorial/images/tutorial_image018.png
686 @image latex /tutorial/images/tutorial_image018.png
688 * Initialize the algorithm by creating an instance of the class. The first parameter of this constructor must be specified if you want to create a solid. By default, *BRepOffsetAPI_ThruSections* builds a shell.
689 * Add the successive wires using the AddWire method.
690 * Use the *CheckCompatibility* method to activate (or deactivate) the option that checks whether the wires have the same number of edges. In this case, wires have two edges each, so you can deactivate this option.
691 * Ask for the resulting loft shape with the Shape method.
693 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
694 BRepOffsetAPI_ThruSections aTool(Standard_True);
695 aTool.AddWire(threadingWire1); aTool.AddWire(threadingWire2);
696 aTool.CheckCompatibility(Standard_False);
697 TopoDS_Shape myThreading = aTool.Shape();
698 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
701 @section sec5 Building the Resulting Compound
704 You are almost done building the bottle. Use the *TopoDS_Compound* and *BRep_Builder* classes to build single shape from *myBody* and *myThreading*:
706 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
707 TopoDS_Compound aRes;
708 BRep_Builder aBuilder;
709 aBuilder.MakeCompound (aRes);
710 aBuilder.Add (aRes, myBody);
711 aBuilder.Add (aRes, myThreading);
712 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
714 Congratulations! Your bottle is complete. Here is the result snapshot of the Tutorial application:
716 @image html /tutorial/images/tutorial_image019.png
717 @image latex /tutorial/images/tutorial_image019.png
719 We hope that this tutorial has provided you with a feel for the industrial strength power of Open CASCADE Technology.
720 If you want to know more and develop major projects using Open CASCADE Technology, we invite you to study our training, support, and consulting services on our site at http://www.opencascade.org/support. Our professional services can maximize the power of your Open CASCADE Technology applications.
723 @section sec6 Appendix
726 Complete definition of MakeBottle function (defined in the file src/MakeBottle.cxx of the Tutorial):
728 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
729 TopoDS_Shape MakeBottle(const Standard_Real myWidth, const Standard_Real myHeight,
730 const Standard_Real myThickness)
732 // Profile : Define Support Points
733 gp_Pnt aPnt1(-myWidth / 2., 0, 0);
734 gp_Pnt aPnt2(-myWidth / 2., -myThickness / 4., 0);
735 gp_Pnt aPnt3(0, -myThickness / 2., 0);
736 gp_Pnt aPnt4(myWidth / 2., -myThickness / 4., 0);
737 gp_Pnt aPnt5(myWidth / 2., 0, 0);
739 // Profile : Define the Geometry
740 Handle(Geom_TrimmedCurve) anArcOfCircle = GC_MakeArcOfCircle(aPnt2,aPnt3,aPnt4);
741 Handle(Geom_TrimmedCurve) aSegment1 = GC_MakeSegment(aPnt1, aPnt2);
742 Handle(Geom_TrimmedCurve) aSegment2 = GC_MakeSegment(aPnt4, aPnt5);
744 // Profile : Define the Topology
745 TopoDS_Edge anEdge1 = BRepBuilderAPI_MakeEdge(aSegment1);
746 TopoDS_Edge anEdge2 = BRepBuilderAPI_MakeEdge(anArcOfCircle);
747 TopoDS_Edge anEdge3 = BRepBuilderAPI_MakeEdge(aSegment2);
748 TopoDS_Wire aWire = BRepBuilderAPI_MakeWire(anEdge1, anEdge2, anEdge3);
751 gp_Ax1 xAxis = gp::OX();
754 aTrsf.SetMirror(xAxis);
755 BRepBuilderAPI_Transform aBRepTrsf(aWire, aTrsf);
756 TopoDS_Shape aMirroredShape = aBRepTrsf.Shape();
757 TopoDS_Wire aMirroredWire = TopoDS::Wire(aMirroredShape);
759 BRepBuilderAPI_MakeWire mkWire;
761 mkWire.Add(aMirroredWire);
762 TopoDS_Wire myWireProfile = mkWire.Wire();
764 // Body : Prism the Profile
765 TopoDS_Face myFaceProfile = BRepBuilderAPI_MakeFace(myWireProfile);
766 gp_Vec aPrismVec(0, 0, myHeight);
767 TopoDS_Shape myBody = BRepPrimAPI_MakePrism(myFaceProfile, aPrismVec);
769 // Body : Apply Fillets
770 BRepFilletAPI_MakeFillet mkFillet(myBody);
771 TopExp_Explorer anEdgeExplorer(myBody, TopAbs_EDGE);
772 while(anEdgeExplorer.More()){
773 TopoDS_Edge anEdge = TopoDS::Edge(anEdgeExplorer.Current());
774 //Add edge to fillet algorithm
775 mkFillet.Add(myThickness / 12., anEdge);
776 anEdgeExplorer.Next();
779 myBody = mkFillet.Shape();
781 // Body : Add the Neck
782 gp_Pnt neckLocation(0, 0, myHeight);
783 gp_Dir neckAxis = gp::DZ();
784 gp_Ax2 neckAx2(neckLocation, neckAxis);
786 Standard_Real myNeckRadius = myThickness / 4.;
787 Standard_Real myNeckHeight = myHeight / 10.;
789 BRepPrimAPI_MakeCylinder MKCylinder(neckAx2, myNeckRadius, myNeckHeight);
790 TopoDS_Shape myNeck = MKCylinder.Shape();
792 myBody = BRepAlgoAPI_Fuse(myBody, myNeck);
794 // Body : Create a Hollowed Solid
795 TopoDS_Face faceToRemove;
796 Standard_Real zMax = -1;
798 for(TopExp_Explorer aFaceExplorer(myBody, TopAbs_FACE); aFaceExplorer.More(); aFaceExplorer.Next()){
799 TopoDS_Face aFace = TopoDS::Face(aFaceExplorer.Current());
800 // Check if <aFace> is the top face of the bottle's neck
801 Handle(Geom_Surface) aSurface = BRep_Tool::Surface(aFace);
802 if(aSurface->DynamicType() == STANDARD_TYPE(Geom_Plane)){
803 Handle(Geom_Plane) aPlane = Handle(Geom_Plane)::DownCast(aSurface);
804 gp_Pnt aPnt = aPlane->Location();
805 Standard_Real aZ = aPnt.Z();
808 faceToRemove = aFace;
813 TopTools_ListOfShape facesToRemove;
814 facesToRemove.Append(faceToRemove);
815 myBody = BRepOffsetAPI_MakeThickSolid(myBody, facesToRemove, -myThickness / 50, 1.e-3);
816 // Threading : Create Surfaces
817 Handle(Geom_CylindricalSurface) aCyl1 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 0.99);
818 Handle(Geom_CylindricalSurface) aCyl2 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 1.05);
820 // Threading : Define 2D Curves
821 gp_Pnt2d aPnt(2. * M_PI, myNeckHeight / 2.);
822 gp_Dir2d aDir(2. * M_PI, myNeckHeight / 4.);
823 gp_Ax2d anAx2d(aPnt, aDir);
825 Standard_Real aMajor = 2. * M_PI;
826 Standard_Real aMinor = myNeckHeight / 10;
828 Handle(Geom2d_Ellipse) anEllipse1 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor);
829 Handle(Geom2d_Ellipse) anEllipse2 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor / 4);
830 Handle(Geom2d_TrimmedCurve) anArc1 = new Geom2d_TrimmedCurve(anEllipse1, 0, M_PI);
831 Handle(Geom2d_TrimmedCurve) anArc2 = new Geom2d_TrimmedCurve(anEllipse2, 0, M_PI);
832 gp_Pnt2d anEllipsePnt1 = anEllipse1->Value(0);
833 gp_Pnt2d anEllipsePnt2 = anEllipse1->Value(M_PI);
835 Handle(Geom2d_TrimmedCurve) aSegment = GCE2d_MakeSegment(anEllipsePnt1, anEllipsePnt2);
836 // Threading : Build Edges and Wires
837 TopoDS_Edge anEdge1OnSurf1 = BRepBuilderAPI_MakeEdge(anArc1, aCyl1);
838 TopoDS_Edge anEdge2OnSurf1 = BRepBuilderAPI_MakeEdge(aSegment, aCyl1);
839 TopoDS_Edge anEdge1OnSurf2 = BRepBuilderAPI_MakeEdge(anArc2, aCyl2);
840 TopoDS_Edge anEdge2OnSurf2 = BRepBuilderAPI_MakeEdge(aSegment, aCyl2);
841 TopoDS_Wire threadingWire1 = BRepBuilderAPI_MakeWire(anEdge1OnSurf1, anEdge2OnSurf1);
842 TopoDS_Wire threadingWire2 = BRepBuilderAPI_MakeWire(anEdge1OnSurf2, anEdge2OnSurf2);
843 BRepLib::BuildCurves3d(threadingWire1);
844 BRepLib::BuildCurves3d(threadingWire2);
847 BRepOffsetAPI_ThruSections aTool(Standard_True);
848 aTool.AddWire(threadingWire1);
849 aTool.AddWire(threadingWire2);
850 aTool.CheckCompatibility(Standard_False);
852 TopoDS_Shape myThreading = aTool.Shape();
854 // Building the Resulting Compound
855 TopoDS_Compound aRes;
856 BRep_Builder aBuilder;
857 aBuilder.MakeCompound (aRes);
858 aBuilder.Add (aRes, myBody);
859 aBuilder.Add (aRes, myThreading);
863 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~