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ba06f8bb 1 Tutorial {#occt__tutorial}
765b3e07 2=======
3
e5bd0d98 4@tableofcontents
5
765b3e07 6@section sec1 Overview
7
8
9This 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.
10
11
12@subsection OCCT_TUTORIAL_SUB1_1 Prerequisites
13
14This tutorial assumes that you have experience in using and setting up C++.
15From 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.
16
17@subsection OCCT_TUTORIAL_SUB1_2 The Model
18
19To illustrate the use of classes provided in the 3D geometric modeling toolkits, you will create a bottle as shown:
20
d6b4d3d0 21@figure{/tutorial/images/tutorial_image001.png,"",240}
765b3e07 22
23In 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.
24
25@subsection OCCT_TUTORIAL_SUB1_3 Model Specifications
26
27We first define the bottle specifications as follows:
28
29| Object Parameter | Parameter Name | Parameter Value |
30| :--------------: | :------------: | :-------------: |
31| Bottle height | MyHeight | 70mm |
32| Bottle width | MyWidth | 50mm |
33| Bottle thickness | MyThickness | 30mm |
34
35In addition, we decide that the bottle's profile (base) will be centered on the origin of the global Cartesian coordinate system.
36
d6b4d3d0 37@figure{/tutorial/images/tutorial_image002.png,"",240}
765b3e07 38
39This modeling requires four steps:
40
41 * build the bottle's Profile
42 * build the bottle's Body
43 * build the Threading on the bottle's neck
44 * build the result compound
45
46
47@section sec2 Building the Profile
48
49@subsection OCCT_TUTORIAL_SUB2_1 Defining Support Points
50
51To 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.
52
d6b4d3d0 53@figure{tutorial/images/tutorial_image003.svg,"",466}
765b3e07 54
55There are two classes to describe a 3D Cartesian point from its X, Y and Z coordinates in Open CASCADE Technology:
56
57 * the primitive geometric *gp_Pnt* class
58 * the transient *Geom_CartesianPoint* class manipulated by handle
59
60A handle is a type of smart pointer that provides automatic memory management.
61To choose the best class for this application, consider the following:
62
63 * *gp_Pnt* is manipulated by value. Like all objects of its kind, it will have a limited lifetime.
64 * *Geom_CartesianPoint* is manipulated by handle and may have multiple references and a long lifetime.
65
66Since 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.
3d68eaf5 67To instantiate a *gp_Pnt* object, just specify the X, Y, and Z coordinates of the points in the global Cartesian coordinate system:
765b3e07 68
69~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
70 gp_Pnt aPnt1(-myWidth / 2., 0, 0);
71 gp_Pnt aPnt2(-myWidth / 2., -myThickness / 4., 0);
72 gp_Pnt aPnt3(0, -myThickness / 2., 0);
73 gp_Pnt aPnt4(myWidth / 2., -myThickness / 4., 0);
74 gp_Pnt aPnt5(myWidth / 2., 0, 0);
75~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
76
77Once 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:
78
79~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
80Standard_Real xValue1 = aPnt1.X();
81~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
82
83@subsection OCCT_TUTORIAL_SUB2_2 Profile: Defining the Geometry
84With 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.
85
d6b4d3d0 86@figure{/tutorial/images/tutorial_image004.png,"",240}
765b3e07 87
88To 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.
89In 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*).
90However, 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.
91This is because the *GC* provides two algorithm classes which are exactly what is required for our profile:
92
93 * Class *GC_MakeSegment* to create a segment. One of its constructors allows you to define a segment by two end points P1 and P2
94 * 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.
95
96Both 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.
97
98~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
99 Handle(Geom_TrimmedCurve) aArcOfCircle = GC_MakeArcOfCircle(aPnt2,aPnt3,aPnt4);
100 Handle(Geom_TrimmedCurve) aSegment1 = GC_MakeSegment(aPnt1, aPnt2);
101 Handle(Geom_TrimmedCurve) aSegment2 = GC_MakeSegment(aPnt4, aPnt5);
102~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
103
104All *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:
105
106~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
107 GC_MakeSegment mkSeg (aPnt1, aPnt2);
108 Handle(Geom_TrimmedCurve) aSegment1;
109 if(mkSegment.IsDone()){
110 aSegment1 = mkSeg.Value();
111 }
112 else {
113 // handle error
114 }
115~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
116
117
118@subsection OCCT_TUTORIAL_SUB2_3 Profile: Defining the Topology
119
120
121You have created the support geometry of one part of the profile but these curves are independent with no relations between each other.
122To simplify the modeling, it would be right to manipulate these three curves as a single entity.
123This 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.
124Each object of the *TopoDS* package, inheriting from the *TopoDS_Shape* class, describes a topological shape as described below:
125
126| Shape | Open CASCADE Technology Class | Description |
127| :-------- | :---------------------------- | :------------------------------------------------------------ |
128| Vertex | TopoDS_Vertex | Zero dimensional shape corresponding to a point in geometry. |
129| Edge | TopoDS_Edge | One-dimensional shape corresponding to a curve and bounded by a vertex at each extremity.|
130| Wire | TopoDS_Wire | Sequence of edges connected by vertices. |
131| Face | TopoDS_Face | Part of a surface bounded by a closed wire(s). |
132| Shell | TopoDS_Shell | Set of faces connected by edges. |
133| Solid | TopoDS_Solid | Part of 3D space bounded by Shells. |
134| CompSolid | TopoDS_CompSolid | Set of solids connected by their faces. |
135| Compound | TopoDS_Compound | Set of any other shapes described above. |
136
137Referring to the previous table, to build the profile, you will create:
138
139 * Three edges out of the previously computed curves.
140 * One wire with these edges.
141
d6b4d3d0 142@figure{/tutorial/images/tutorial_image005.png,"",240}
765b3e07 143
144However, 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.
145To create an edge, you use the BRepBuilderAPI_MakeEdge class with the previously computed curves:
146
147~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
148 TopoDS_Edge aEdge1 = BRepBuilderAPI_MakeEdge(aSegment1);
149 TopoDS_Edge aEdge2 = BRepBuilderAPI_MakeEdge(aArcOfCircle);
150 TopoDS_Edge aEdge3 = BRepBuilderAPI_MakeEdge(aSegment2);
151~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
152
153In 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:
154
155~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
156 TopoDS_Edge aEdge1 = BRepBuilderAPI_MakeEdge(aPnt1, aPnt3);
157 TopoDS_Edge aEdge2 = BRepBuilderAPI_MakeEdge(aPnt4, aPnt5);
158~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
159
160To 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:
161
162 * directly from one to four edges
163 * by adding other wire(s) or edge(s) to an existing wire (this is explained later in this tutorial)
164
165When building a wire from less than four edges, as in the present case, you can use the constructor directly as follows:
166
167~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
168 TopoDS_Wire aWire = BRepBuilderAPI_MakeWire(aEdge1, aEdge2, aEdge3);
169~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
170
171
172@subsection OCCT_TUTORIAL_SUB2_4 Profile: Completing the Profile
173
174
175Once the first part of your wire is created you need to compute the complete profile. A simple way to do this is to:
176
177 * compute a new wire by reflecting the existing one.
178 * add the reflected wire to the initial one.
179
d6b4d3d0 180@figure{/tutorial/images/tutorial_image006.png,"",377}
765b3e07 181
182To 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.
183In 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.
184The first way is to define it from scratch, using its geometric definition:
185
186 * X axis is located at (0, 0, 0) - use the *gp_Pnt* class.
187 * 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.
188
189~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
190 gp_Pnt aOrigin(0, 0, 0);
191 gp_Dir xDir(1, 0, 0);
192 gp_Ax1 xAxis(aOrigin, xDir);
193~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
194
195The 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:
196
197~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
198 gp_Ax1 xAxis = gp::OX();
199~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
200
201As previously explained, the 3D geometric transformation is defined with the *gp_Trsf* class. There are two different ways to use this class:
202
203 * by defining a transformation matrix by all its values
204 * by using the appropriate methods corresponding to the required transformation (SetTranslation for a translation, SetMirror for a reflection, etc.): the matrix is automatically computed.
205
206Since the simplest approach is always the best one, you should use the SetMirror method with the axis as the center of symmetry.
207
208~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
209 gp_Trsf aTrsf;
210 aTrsf.SetMirror(xAxis);
211~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
212
213You now have all necessary data to apply the transformation with the BRepBuilderAPI_Transform class by specifying:
214
215 * the shape on which the transformation must be applied.
216 * the geometric transformation
217
218~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
219 BRepBuilderAPI_Transform aBRepTrsf(aWire, aTrsf);
220~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
221
222*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:
223
224~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
225 TopoDS_Shape aMirroredShape = aBRepTrsf.Shape();
226~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
227
228What 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.
229
230~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
231 TopoDS_Wire aMirroredWire = TopoDS::Wire(aMirroredShape);
232~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
233
234The 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:
235
236 * create an instance of *BRepBuilderAPI_MakeWire*.
237 * add all edges of the two wires by using the *Add* method on this object.
238
239~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
240 BRepBuilderAPI_MakeWire mkWire;
241 mkWire.Add(aWire);
242 mkWire.Add(aMirroredWire);
243 TopoDS_Wire myWireProfile = mkWire.Wire();
244~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
245
246
247@section sec3 Building the Body
248
249
250@subsection OCCT_TUTORIAL_SUB3_1 Prism the Profile
251
252
253To 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:
254
255| Shape | Generates |
256| :----- | :----------------- |
257| Vertex | Edge |
258| Edge | Face |
259| Wire | Shell |
260| Face | Solid |
261| Shell | Compound of Solids |
262
d6b4d3d0 263@figure{/tutorial/images/tutorial_image007.png,"",240}
765b3e07 264
265Your 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.
266To 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.
267When the wire lies on a plane, the surface is automatically computed.
268
269~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
270 TopoDS_Face myFaceProfile = BRepBuilderAPI_MakeFace(myWireProfile);
271~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
272
273The *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:
274
275 * the basis shape to sweep;
276 * a vector for a finite prism or a direction for finite and infinite prisms.
277
278You 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:
279
280~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
281 gp_Vec aPrismVec(0, 0, myHeight);
282~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
283
284All the necessary data to create the main body of your bottle is now available. Just apply the *BRepPrimAPI_MakePrism* class to compute the solid:
285
286~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
287 TopoDS_Shape myBody = BRepPrimAPI_MakePrism(myFaceProfile, aPrismVec);
288~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
289
290
291@subsection OCCT_TUTORIAL_SUB3_2 Applying Fillets
292
293
294The edges of the bottle's body are very sharp. To replace them by rounded faces, you use the *Fillet* functionality of Open CASCADE Technology.
295For our purposes, we will specify that fillets must be:
296
297 * applied on all edges of the shape
298 * have a radius of *myThickness* / 12
299
d6b4d3d0 300@figure{/tutorial/images/tutorial_image008.png,"",240}
765b3e07 301
302To apply fillets on the edges of a shape, you use the *BRepFilletAPI_MakeFillet* class. This class is normally used as follows:
303
304 * Specify the shape to be filleted in the *BRepFilletAPI_MakeFillet* constructor.
305 * Add the fillet descriptions (an edge and a radius) using the *Add* method (you can add as many edges as you need).
306 * Ask for the resulting filleted shape with the *Shape* method.
307
308~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
309BRepFilletAPI_MakeFillet mkFillet(myBody);
310~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
311
312To 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.
313Generally, this explorer is created by providing the following information:
314
315 * the shape to explore
316 * the type of sub-shapes to be found. This information is given with the *TopAbs_ShapeEnum* enumeration.
317
318~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
319TopExp_Explorer anEdgeExplorer(myBody, TopAbs_EDGE);
320~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
321
322An explorer is usually applied in a loop by using its three main methods:
323
324 * *More()* to know if there are more sub-shapes to explore.
325 * *Current()* to know which is the currently explored sub-shape (used only if the *More()* method returns true).
326 * *Next()* to move onto the next sub-shape to explore.
327
328
329~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
330 while(anEdgeExplorer.More()){
331 TopoDS_Edge anEdge = TopoDS::Edge(anEdgeExplorer.Current());
332 //Add edge to fillet algorithm
333 ...
334 anEdgeExplorer.Next();
335 }
336~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
337
338In 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.
339
340~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
341 mkFillet.Add(myThickness / 12., anEdge);
342~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
343
344Once this is done, you perform the last step of the procedure by asking for the filleted shape.
345
346~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
347 myBody = mkFillet.Shape();
348~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
349
350
351@subsection OCCT_TUTORIAL_SUB3_3 Adding the Neck
352
353
354To 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.
355
d6b4d3d0 356@figure{/tutorial/images/tutorial_image009.png,"",240}
765b3e07 357
358To 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).
359To 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:
360
361~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
362 gp_Pnt neckLocation(0, 0, myHeight);
363 gp_Dir neckAxis = gp::DZ();
364 gp_Ax2 neckAx2(neckLocation, neckAxis);
365~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
366
367To create a cylinder, use another class from the primitives construction package: the *BRepPrimAPI_MakeCylinder* class. The information you must provide is:
368
369 * the coordinate system where the cylinder will be located;
370 * the radius and height.
371
372~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
373 Standard_Real myNeckRadius = myThickness / 4.;
374 Standard_Real myNeckHeight = myHeight / 10;
375 BRepPrimAPI_MakeCylinder MKCylinder(neckAx2, myNeckRadius, myNeckHeight);
376 TopoDS_Shape myNeck = MKCylinder.Shape();
377~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
378
379You now have two separate parts: a main body and a neck that you need to fuse together.
380The *BRepAlgoAPI* package provides services to perform Boolean operations between shapes, and especially: *common* (Boolean intersection), *cut* (Boolean subtraction) and *fuse* (Boolean union).
381Use *BRepAlgoAPI_Fuse* to fuse the two shapes:
382
383~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
384 myBody = BRepAlgoAPI_Fuse(myBody, myNeck);
385~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
386
387
388@subsection OCCT_TUTORIAL_SUB3_4 Creating a Hollowed Solid
389
390
391Since a real bottle is used to contain liquid material, you should now create a hollowed solid from the bottle's top face.
392In Open CASCADE Technology, a hollowed solid is called a *Thick* *Solid* and is internally computed as follows:
393
394 * Remove one or more faces from the initial solid to obtain the first wall W1 of the hollowed solid.
395 * 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.
396 * Compute a solid from the two walls W1 and W2.
397
d6b4d3d0 398@figure{/tutorial/images/tutorial_image010.png,"",240}
765b3e07 399
400To compute a thick solid, you create an instance of the *BRepOffsetAPI_MakeThickSolid* class by giving the following information:
401
402 * The shape, which must be hollowed.
403 * The tolerance used for the computation (tolerance criterion for coincidence in generated shapes).
404 * The thickness between the two walls W1 and W2 (distance D).
405 * The face(s) to be removed from the original solid to compute the first wall W1.
406
407The challenging part in this procedure is to find the face to remove from your shape - the top face of the neck, which:
408
409 * has a plane (planar surface) as underlying geometry;
410 * is the highest face (in Z coordinates) of the bottle.
411
412To 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.
413
414~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
415 for(TopExp_Explorer aFaceExplorer(myBody, TopAbs_FACE) ; aFaceExplorer.More() ; aFaceExplorer.Next()){
416 TopoDS_Face aFace = TopoDS::Face(aFaceExplorer.Current());
417 }
418~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
419
420For 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:
421
422 * *Surface* to access the surface of a face;
423 * *Curve* to access the 3D curve of an edge;
424 * *Point* to access the 3D point of a vertex.
425
426~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
427Handle(Geom_Surface) aSurface = BRep_Tool::Surface(aFace);
428~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
429
430As 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.
431All objects manipulated by handle, like *Geom_Surface*, inherit from the *Standard_Transient* class which provides two very useful methods concerning types:
432
433 * *DynamicType* to know the real type of the object
434 * *IsKind* to know if the object inherits from one particular type
435
436DynamicType 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.
437To compare a given type with the type you seek, use the *STANDARD_TYPE* macro, which returns the type of a class:
438
439~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
440 if(aSurface->DynamicType() == STANDARD_TYPE(Geom_Plane)){
441 //
442 }
443~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
444
445If 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:
446
447~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
448 Handle(Geom_Plane) aPlane = Handle(Geom_Plane)::DownCast(aSurface);
449~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
450
451Remember 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:
452
453~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
454 TopoDS_Face faceToRemove;
455 Standard_Real zMax = -1;
456~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
457
458You 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:
459
460~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
461 gp_Pnt aPnt = aPlane->Location();
462 Standard_Real aZ = aPnt.Z();
463 if(aZ > zMax){
464 zMax = aZ;
465 faceToRemove = aFace;
466 }
467~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
468
469You 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.
470Open 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.
471The collection for shapes can be found in the *TopTools* package. As *BRepOffsetAPI_MakeThickSolid* requires a list, use the *TopTools_ListOfShape* class.
472
473~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
474 TopTools_ListOfShape facesToRemove;
475 facesToRemove.Append(faceToRemove);
476~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
477
8013367c 478All the necessary data are now available so you can create your hollowed solid by calling the *BRepOffsetAPI_MakeThickSolid* MakeThickSolidByJoin method:
765b3e07 479
480~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
8013367c 481 BRepOffsetAPI_MakeThickSolid BodyMaker;
482 BodyMaker.MakeThickSolidByJoin(myBody, facesToRemove, -myThickness / 50, 1.e-3);
483 myBody = BodyMaker.Shape();
765b3e07 484~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
485
486
487@section sec4 Building the Threading
488
489
490@subsection OCCT_TUTORIAL_SUB4_1 Creating Surfaces
491
492
493Up to now, you have learned how to create edges out of 3D curves.
494You will now learn how to create an edge out of a 2D curve and a surface.
495To 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.
496As 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:
497
498 * a coordinate system;
499 * a radius.
500
501Using the same coordinate system *neckAx2* used to position the neck, you create two cylindrical surfaces *Geom_CylindricalSurface* with the following radii:
502
d6b4d3d0 503@figure{/tutorial/images/tutorial_image011.png,"",300}
765b3e07 504
505Notice 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.
506
507~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
508 Handle(Geom_CylindricalSurface) aCyl1 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 0.99);
509
510 Handle(Geom_CylindricalSurface) aCyl2 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 1.05);
511~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
512
513
514@subsection OCCT_TUTORIAL_SUB4_2 Defining 2D Curves
515
516
517To 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.
518All geometries defined in the *Geom* package are parameterized. This means that each curve or surface from Geom is computed with a parametric equation.
519A *Geom_CylindricalSurface* surface is defined with the following parametric equation:
520
521P(U, V) = O + R * (cos(U) * xDir + sin(U) * yDir) + V * zDir, where :
522
523 * P is the point defined by parameters (U, V).
524 * O, *Dir, yDir and zDir are respectively the origin, the X direction, Y direction and Z direction of the cylindrical surface local coordinate system.
525 * R is the radius of the cylindrical surface.
526 * U range is [0, 2PI] and V is infinite.
527
d6b4d3d0 528@figure{/tutorial/images/tutorial_image012.png,"",400}
765b3e07 529
530The advantage of having such parameterized geometries is that you can compute, for any (U, V) parameters of the surface:
531
532 * the 3D point;
533 * the derivative vectors of order 1, 2 to N at this point.
534
535There 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:
536
d6b4d3d0 537@figure{/tutorial/images/tutorial_image013.png,"",320}
765b3e07 538
539Suppose 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:
540
541| Case | Parametric Equation | Parametric Curve |
542| :------------ | :----------------------------------------------------------- | :---------------------------------------------------------------------------- |
543| U = 0 | P(V) = O + V * zDir | Line parallel to the Z direction |
544| V = 0 | P(U) = O + R * (cos(U) * xDir + sin(U) * yDir) | Circle parallel to the (O, X, Y) plane |
545| 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 |
546
547The helicoidal curve type is exactly what you need. On the neck's surface, the evolution laws of this curve will be:
548
549 * In V parameter: between 0 and myHeighNeck for the height description
550 * 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:
551
d6b4d3d0 552@figure{/tutorial/images/tutorial_image014.png,"",440}
765b3e07 553
554In 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:
555
556 * A center located in the middle of the neck's cylinder parametric space at (2*PI, myNeckHeight / 2) in U, V coordinates.
557 * 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.
558
d6b4d3d0 559@figure{/tutorial/images/tutorial_image015.png,"",440}
765b3e07 560
561To 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:
562
563 * To define a 2D point from its X and Y coordinates, use the *gp_Pnt2d* class.
564 * To define a 2D direction (unit vector) from its X and Y coordinates, use the gp_Dir2d class. The coordinates will automatically be normalized.
565 * 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.
566
567~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
568 gp_Pnt2d aPnt(2. * M_PI, myNeckHeight / 2.);
569 gp_Dir2d aDir(2. * M_PI, myNeckHeight / 4.);
570 gp_Ax2d anAx2d(aPnt, aDir);
571~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
572
573You 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).
574
d6b4d3d0 575@figure{/tutorial/images/tutorial_image016.png,"",440}
765b3e07 576
577You 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:
578
579 * a coordinate system whose origin is the ellipse center;
580 * a major radius on the major axis defined by the X direction of the coordinate system;
581 * a minor radius on the minor axis defined by the Y direction of the coordinate system.
582
583Supposing that:
584
585 * Both ellipses have the same major radius of 2*PI,
586 * Minor radius of the first ellipse is myNeckHeight / 10,
587 * And the minor radius value of the second ellipse is a fourth of the first one,
588
589Your ellipses are defined as follows:
590
591~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
592 Standard_Real aMajor = 2. * M_PI;
593 Standard_Real aMinor = myNeckHeight / 10;
594 Handle(Geom2d_Ellipse) anEllipse1 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor);
595 Handle(Geom2d_Ellipse) anEllipse2 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor / 4);
596~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
597
598To 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.
599As 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.
600
601~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
602 Handle(Geom2d_TrimmedCurve) anArc1 = new Geom2d_TrimmedCurve(anEllipse1, 0, M_PI);
603 Handle(Geom2d_TrimmedCurve) anArc2 = new Geom2d_TrimmedCurve(anEllipse2, 0, M_PI);
604~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
605
606The 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.
607To 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.
608
609~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
610 gp_Pnt2d anEllipsePnt1 = anEllipse1->Value(0);
611 gp_Pnt2d anEllipsePnt2;
612 anEllipse1->D0(M_PI, anEllipsePnt2);
613~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
614
615When creating the bottle's profile, you used classes from the *GC* package, providing algorithms to create elementary geometries.
616In 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:
617
618~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
619 Handle(Geom2d_TrimmedCurve) aSegment = GCE2d_MakeSegment(anEllipsePnt1, anEllipsePnt2);
620~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
621
622
623@subsection OCCT_TUTORIAL_SUB4_3 Building Edges and Wires
624
625
626As you did when creating the base profile of the bottle, you can now:
627
628 * compute the edges of the neck's threading.
629 * compute two wires out of these edges.
630
d6b4d3d0 631@figure{/tutorial/images/tutorial_image017.png,"",440}
765b3e07 632
633Previously, you have built:
634
635 * two cylindrical surfaces of the threading
636 * three 2D curves defining the base geometry of the threading
637
638To 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.
639
640~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
641 TopoDS_Edge anEdge1OnSurf1 = BRepBuilderAPI_MakeEdge(anArc1, aCyl1);
642 TopoDS_Edge anEdge2OnSurf1 = BRepBuilderAPI_MakeEdge(aSegment, aCyl1);
643 TopoDS_Edge anEdge1OnSurf2 = BRepBuilderAPI_MakeEdge(anArc2, aCyl2);
644 TopoDS_Edge anEdge2OnSurf2 = BRepBuilderAPI_MakeEdge(aSegment, aCyl2);
645~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
646
647Now, you can create the two profiles of the threading, lying on each surface.
648
649~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
650 TopoDS_Wire threadingWire1 = BRepBuilderAPI_MakeWire(anEdge1OnSurf1, anEdge2OnSurf1);
651 TopoDS_Wire threadingWire2 = BRepBuilderAPI_MakeWire(anEdge1OnSurf2, anEdge2OnSurf2);
652~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
653
654Remember that these wires were built out of a surface and 2D curves.
655One 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.
656When 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.
657
658~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
659 BRepLib::BuildCurves3d(threadingWire1);
660 BRepLib::BuildCurves3d(threadingWire2);
661~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
662
663
664@subsection OCCT_TUTORIAL_SUB4_4 Creating Threading
665
666
667You 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.
668There 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.
669The loft function is implemented in the *BRepOffsetAPI_ThruSections* class, which you use as follows:
670
d6b4d3d0 671@figure{/tutorial/images/tutorial_image018.png,"",285}
765b3e07 672
673 * 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.
674 * Add the successive wires using the AddWire method.
675 * 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.
676 * Ask for the resulting loft shape with the Shape method.
677
678~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
679 BRepOffsetAPI_ThruSections aTool(Standard_True);
680 aTool.AddWire(threadingWire1); aTool.AddWire(threadingWire2);
681 aTool.CheckCompatibility(Standard_False);
682 TopoDS_Shape myThreading = aTool.Shape();
683~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
684
685
686@section sec5 Building the Resulting Compound
687
688
689You are almost done building the bottle. Use the *TopoDS_Compound* and *BRep_Builder* classes to build single shape from *myBody* and *myThreading*:
690
691~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
692 TopoDS_Compound aRes;
693 BRep_Builder aBuilder;
694 aBuilder.MakeCompound (aRes);
695 aBuilder.Add (aRes, myBody);
696 aBuilder.Add (aRes, myThreading);
697~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
698
699Congratulations! Your bottle is complete. Here is the result snapshot of the Tutorial application:
700
d6b4d3d0 701@figure{/tutorial/images/tutorial_image019.png,"",320}
765b3e07 702
703We hope that this tutorial has provided you with a feel for the industrial strength power of Open CASCADE Technology.
7863dabb 704If 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 https://www.opencascade.com/content/technology-support. Our professional services can maximize the power of your Open CASCADE Technology applications.
765b3e07 705
706
707@section sec6 Appendix
708
709
710Complete definition of MakeBottle function (defined in the file src/MakeBottle.cxx of the Tutorial):
711
712~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
713 TopoDS_Shape MakeBottle(const Standard_Real myWidth, const Standard_Real myHeight,
714 const Standard_Real myThickness)
715 {
716 // Profile : Define Support Points
717 gp_Pnt aPnt1(-myWidth / 2., 0, 0);
718 gp_Pnt aPnt2(-myWidth / 2., -myThickness / 4., 0);
719 gp_Pnt aPnt3(0, -myThickness / 2., 0);
720 gp_Pnt aPnt4(myWidth / 2., -myThickness / 4., 0);
721 gp_Pnt aPnt5(myWidth / 2., 0, 0);
722
723 // Profile : Define the Geometry
724 Handle(Geom_TrimmedCurve) anArcOfCircle = GC_MakeArcOfCircle(aPnt2,aPnt3,aPnt4);
725 Handle(Geom_TrimmedCurve) aSegment1 = GC_MakeSegment(aPnt1, aPnt2);
726 Handle(Geom_TrimmedCurve) aSegment2 = GC_MakeSegment(aPnt4, aPnt5);
727
728 // Profile : Define the Topology
729 TopoDS_Edge anEdge1 = BRepBuilderAPI_MakeEdge(aSegment1);
730 TopoDS_Edge anEdge2 = BRepBuilderAPI_MakeEdge(anArcOfCircle);
731 TopoDS_Edge anEdge3 = BRepBuilderAPI_MakeEdge(aSegment2);
732 TopoDS_Wire aWire = BRepBuilderAPI_MakeWire(anEdge1, anEdge2, anEdge3);
733
734 // Complete Profile
735 gp_Ax1 xAxis = gp::OX();
736 gp_Trsf aTrsf;
737
738 aTrsf.SetMirror(xAxis);
739 BRepBuilderAPI_Transform aBRepTrsf(aWire, aTrsf);
740 TopoDS_Shape aMirroredShape = aBRepTrsf.Shape();
741 TopoDS_Wire aMirroredWire = TopoDS::Wire(aMirroredShape);
742
743 BRepBuilderAPI_MakeWire mkWire;
744 mkWire.Add(aWire);
745 mkWire.Add(aMirroredWire);
746 TopoDS_Wire myWireProfile = mkWire.Wire();
747
748 // Body : Prism the Profile
749 TopoDS_Face myFaceProfile = BRepBuilderAPI_MakeFace(myWireProfile);
750 gp_Vec aPrismVec(0, 0, myHeight);
751 TopoDS_Shape myBody = BRepPrimAPI_MakePrism(myFaceProfile, aPrismVec);
752
753 // Body : Apply Fillets
754 BRepFilletAPI_MakeFillet mkFillet(myBody);
755 TopExp_Explorer anEdgeExplorer(myBody, TopAbs_EDGE);
756 while(anEdgeExplorer.More()){
757 TopoDS_Edge anEdge = TopoDS::Edge(anEdgeExplorer.Current());
758 //Add edge to fillet algorithm
759 mkFillet.Add(myThickness / 12., anEdge);
760 anEdgeExplorer.Next();
761 }
762
763 myBody = mkFillet.Shape();
764
765 // Body : Add the Neck
766 gp_Pnt neckLocation(0, 0, myHeight);
767 gp_Dir neckAxis = gp::DZ();
768 gp_Ax2 neckAx2(neckLocation, neckAxis);
769
770 Standard_Real myNeckRadius = myThickness / 4.;
771 Standard_Real myNeckHeight = myHeight / 10.;
772
773 BRepPrimAPI_MakeCylinder MKCylinder(neckAx2, myNeckRadius, myNeckHeight);
774 TopoDS_Shape myNeck = MKCylinder.Shape();
775
776 myBody = BRepAlgoAPI_Fuse(myBody, myNeck);
777
778 // Body : Create a Hollowed Solid
779 TopoDS_Face faceToRemove;
780 Standard_Real zMax = -1;
781
782 for(TopExp_Explorer aFaceExplorer(myBody, TopAbs_FACE); aFaceExplorer.More(); aFaceExplorer.Next()){
783 TopoDS_Face aFace = TopoDS::Face(aFaceExplorer.Current());
784 // Check if <aFace> is the top face of the bottle's neck
785 Handle(Geom_Surface) aSurface = BRep_Tool::Surface(aFace);
786 if(aSurface->DynamicType() == STANDARD_TYPE(Geom_Plane)){
787 Handle(Geom_Plane) aPlane = Handle(Geom_Plane)::DownCast(aSurface);
788 gp_Pnt aPnt = aPlane->Location();
789 Standard_Real aZ = aPnt.Z();
790 if(aZ > zMax){
791 zMax = aZ;
792 faceToRemove = aFace;
793 }
794 }
795 }
796
797 TopTools_ListOfShape facesToRemove;
798 facesToRemove.Append(faceToRemove);
8013367c 799 BRepOffsetAPI_MakeThickSolid BodyMaker;
800 BodyMaker.MakeThickSolidByJoin(myBody, facesToRemove, -myThickness / 50, 1.e-3);
801 myBody = BodyMaker.Shape();
765b3e07 802 // Threading : Create Surfaces
803 Handle(Geom_CylindricalSurface) aCyl1 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 0.99);
804 Handle(Geom_CylindricalSurface) aCyl2 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 1.05);
805
806 // Threading : Define 2D Curves
807 gp_Pnt2d aPnt(2. * M_PI, myNeckHeight / 2.);
808 gp_Dir2d aDir(2. * M_PI, myNeckHeight / 4.);
809 gp_Ax2d anAx2d(aPnt, aDir);
810
811 Standard_Real aMajor = 2. * M_PI;
812 Standard_Real aMinor = myNeckHeight / 10;
813
814 Handle(Geom2d_Ellipse) anEllipse1 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor);
815 Handle(Geom2d_Ellipse) anEllipse2 = new Geom2d_Ellipse(anAx2d, aMajor, aMinor / 4);
816 Handle(Geom2d_TrimmedCurve) anArc1 = new Geom2d_TrimmedCurve(anEllipse1, 0, M_PI);
817 Handle(Geom2d_TrimmedCurve) anArc2 = new Geom2d_TrimmedCurve(anEllipse2, 0, M_PI);
818 gp_Pnt2d anEllipsePnt1 = anEllipse1->Value(0);
819 gp_Pnt2d anEllipsePnt2 = anEllipse1->Value(M_PI);
820
821 Handle(Geom2d_TrimmedCurve) aSegment = GCE2d_MakeSegment(anEllipsePnt1, anEllipsePnt2);
822 // Threading : Build Edges and Wires
823 TopoDS_Edge anEdge1OnSurf1 = BRepBuilderAPI_MakeEdge(anArc1, aCyl1);
824 TopoDS_Edge anEdge2OnSurf1 = BRepBuilderAPI_MakeEdge(aSegment, aCyl1);
825 TopoDS_Edge anEdge1OnSurf2 = BRepBuilderAPI_MakeEdge(anArc2, aCyl2);
826 TopoDS_Edge anEdge2OnSurf2 = BRepBuilderAPI_MakeEdge(aSegment, aCyl2);
827 TopoDS_Wire threadingWire1 = BRepBuilderAPI_MakeWire(anEdge1OnSurf1, anEdge2OnSurf1);
828 TopoDS_Wire threadingWire2 = BRepBuilderAPI_MakeWire(anEdge1OnSurf2, anEdge2OnSurf2);
829 BRepLib::BuildCurves3d(threadingWire1);
830 BRepLib::BuildCurves3d(threadingWire2);
831
832 // Create Threading
833 BRepOffsetAPI_ThruSections aTool(Standard_True);
834 aTool.AddWire(threadingWire1);
835 aTool.AddWire(threadingWire2);
836 aTool.CheckCompatibility(Standard_False);
837
838 TopoDS_Shape myThreading = aTool.Shape();
839
840 // Building the Resulting Compound
841 TopoDS_Compound aRes;
842 BRep_Builder aBuilder;
843 aBuilder.MakeCompound (aRes);
844 aBuilder.Add (aRes, myBody);
845 aBuilder.Add (aRes, myThreading);
846
847 return aRes;
848 }
849~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d6b4d3d0 850