1 Tutorial {#occt__tutorial}
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 @figure{/tutorial/images/tutorial_image001.png,"",240}
23 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.
25 @subsection OCCT_TUTORIAL_SUB1_3 Model Specifications
27 We first define the bottle specifications as follows:
29 | Object Parameter | Parameter Name | Parameter Value |
30 | :--------------: | :------------: | :-------------: |
31 | Bottle height | MyHeight | 70mm |
32 | Bottle width | MyWidth | 50mm |
33 | Bottle thickness | MyThickness | 30mm |
35 In addition, we decide that the bottle's profile (base) will be centered on the origin of the global Cartesian coordinate system.
37 @figure{/tutorial/images/tutorial_image002.png,"",240}
39 This modeling requires four steps:
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
47 @section sec2 Building the Profile
49 @subsection OCCT_TUTORIAL_SUB2_1 Defining Support Points
51 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.
53 @figure{tutorial/images/tutorial_image003.svg,"",466}
55 There are two classes to describe a 3D Cartesian point from its X, Y and Z coordinates in Open CASCADE Technology:
57 * the primitive geometric *gp_Pnt* class
58 * the transient *Geom_CartesianPoint* class manipulated by handle
60 A handle is a type of smart pointer that provides automatic memory management.
61 To choose the best class for this application, consider the following:
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.
66 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.
67 To instantiate a *gp_Pnt* object, just specify the X, Y, and Z coordinates of the points in the global Cartesian coordinate system:
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
77 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:
79 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
80 Standard_Real xValue1 = aPnt1.X();
81 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
83 @subsection OCCT_TUTORIAL_SUB2_2 Profile: Defining the Geometry
84 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.
86 @figure{/tutorial/images/tutorial_image004.png,"",240}
88 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.
89 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*).
90 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.
91 This is because the *GC* provides two algorithm classes which are exactly what is required for our profile:
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.
96 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.
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
104 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:
106 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
107 GC_MakeSegment mkSeg (aPnt1, aPnt2);
108 Handle(Geom_TrimmedCurve) aSegment1;
109 if(mkSegment.IsDone()){
110 aSegment1 = mkSeg.Value();
115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
118 @subsection OCCT_TUTORIAL_SUB2_3 Profile: Defining the Topology
121 You have created the support geometry of one part of the profile but these curves are independent with no relations between each other.
122 To simplify the modeling, it would be right to manipulate these three curves as a single entity.
123 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.
124 Each object of the *TopoDS* package, inheriting from the *TopoDS_Shape* class, describes a topological shape as described below:
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. |
137 Referring to the previous table, to build the profile, you will create:
139 * Three edges out of the previously computed curves.
140 * One wire with these edges.
142 @figure{/tutorial/images/tutorial_image005.png,"",240}
144 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.
145 To create an edge, you use the BRepBuilderAPI_MakeEdge class with the previously computed curves:
147 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
148 TopoDS_Edge aEdge1 = BRepBuilderAPI_MakeEdge(aSegment1);
149 TopoDS_Edge aEdge2 = BRepBuilderAPI_MakeEdge(aArcOfCircle);
150 TopoDS_Edge aEdge3 = BRepBuilderAPI_MakeEdge(aSegment2);
151 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
153 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:
155 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
156 TopoDS_Edge aEdge1 = BRepBuilderAPI_MakeEdge(aPnt1, aPnt3);
157 TopoDS_Edge aEdge2 = BRepBuilderAPI_MakeEdge(aPnt4, aPnt5);
158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
160 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:
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)
165 When building a wire from less than four edges, as in the present case, you can use the constructor directly as follows:
167 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
168 TopoDS_Wire aWire = BRepBuilderAPI_MakeWire(aEdge1, aEdge2, aEdge3);
169 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
172 @subsection OCCT_TUTORIAL_SUB2_4 Profile: Completing the Profile
175 Once the first part of your wire is created you need to compute the complete profile. A simple way to do this is to:
177 * compute a new wire by reflecting the existing one.
178 * add the reflected wire to the initial one.
180 @figure{/tutorial/images/tutorial_image006.png,"",377}
182 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.
183 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.
184 The first way is to define it from scratch, using its geometric definition:
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.
189 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
190 gp_Pnt aOrigin(0, 0, 0);
191 gp_Dir xDir(1, 0, 0);
192 gp_Ax1 xAxis(aOrigin, xDir);
193 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
195 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:
197 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
198 gp_Ax1 xAxis = gp::OX();
199 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
201 As previously explained, the 3D geometric transformation is defined with the *gp_Trsf* class. There are two different ways to use this class:
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.
206 Since the simplest approach is always the best one, you should use the SetMirror method with the axis as the center of symmetry.
208 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
210 aTrsf.SetMirror(xAxis);
211 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
213 You now have all necessary data to apply the transformation with the BRepBuilderAPI_Transform class by specifying:
215 * the shape on which the transformation must be applied.
216 * the geometric transformation
218 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
219 BRepBuilderAPI_Transform aBRepTrsf(aWire, aTrsf);
220 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:
224 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
225 TopoDS_Shape aMirroredShape = aBRepTrsf.Shape();
226 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
228 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.
230 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
231 TopoDS_Wire aMirroredWire = TopoDS::Wire(aMirroredShape);
232 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
234 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:
236 * create an instance of *BRepBuilderAPI_MakeWire*.
237 * add all edges of the two wires by using the *Add* method on this object.
239 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
240 BRepBuilderAPI_MakeWire mkWire;
242 mkWire.Add(aMirroredWire);
243 TopoDS_Wire myWireProfile = mkWire.Wire();
244 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
247 @section sec3 Building the Body
250 @subsection OCCT_TUTORIAL_SUB3_1 Prism the Profile
253 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:
255 | Shape | Generates |
256 | :----- | :----------------- |
261 | Shell | Compound of Solids |
263 @figure{/tutorial/images/tutorial_image007.png,"",240}
265 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.
266 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.
267 When the wire lies on a plane, the surface is automatically computed.
269 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
270 TopoDS_Face myFaceProfile = BRepBuilderAPI_MakeFace(myWireProfile);
271 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
273 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:
275 * the basis shape to sweep;
276 * a vector for a finite prism or a direction for finite and infinite prisms.
278 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:
280 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
281 gp_Vec aPrismVec(0, 0, myHeight);
282 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
284 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:
286 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
287 TopoDS_Shape myBody = BRepPrimAPI_MakePrism(myFaceProfile, aPrismVec);
288 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
291 @subsection OCCT_TUTORIAL_SUB3_2 Applying Fillets
294 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.
295 For our purposes, we will specify that fillets must be:
297 * applied on all edges of the shape
298 * have a radius of *myThickness* / 12
300 @figure{/tutorial/images/tutorial_image008.png,"",240}
302 To apply fillets on the edges of a shape, you use the *BRepFilletAPI_MakeFillet* class. This class is normally used as follows:
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.
308 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
309 BRepFilletAPI_MakeFillet mkFillet(myBody);
310 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
312 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.
313 Generally, this explorer is created by providing the following information:
315 * the shape to explore
316 * the type of sub-shapes to be found. This information is given with the *TopAbs_ShapeEnum* enumeration.
318 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
319 TopExp_Explorer anEdgeExplorer(myBody, TopAbs_EDGE);
320 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
322 An explorer is usually applied in a loop by using its three main methods:
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.
329 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
330 while(anEdgeExplorer.More()){
331 TopoDS_Edge anEdge = TopoDS::Edge(anEdgeExplorer.Current());
332 //Add edge to fillet algorithm
334 anEdgeExplorer.Next();
336 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
338 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.
340 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
341 mkFillet.Add(myThickness / 12., anEdge);
342 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
344 Once this is done, you perform the last step of the procedure by asking for the filleted shape.
346 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
347 myBody = mkFillet.Shape();
348 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
351 @subsection OCCT_TUTORIAL_SUB3_3 Adding the Neck
354 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.
356 @figure{/tutorial/images/tutorial_image009.png,"",240}
358 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).
359 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:
361 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
362 gp_Pnt neckLocation(0, 0, myHeight);
363 gp_Dir neckAxis = gp::DZ();
364 gp_Ax2 neckAx2(neckLocation, neckAxis);
365 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
367 To create a cylinder, use another class from the primitives construction package: the *BRepPrimAPI_MakeCylinder* class. The information you must provide is:
369 * the coordinate system where the cylinder will be located;
370 * the radius and height.
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
379 You now have two separate parts: a main body and a neck that you need to fuse together.
380 The *BRepAlgoAPI* package provides services to perform Boolean operations between shapes, and especially: *common* (Boolean intersection), *cut* (Boolean subtraction) and *fuse* (Boolean union).
381 Use *BRepAlgoAPI_Fuse* to fuse the two shapes:
383 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
384 myBody = BRepAlgoAPI_Fuse(myBody, myNeck);
385 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
388 @subsection OCCT_TUTORIAL_SUB3_4 Creating a Hollowed Solid
391 Since a real bottle is used to contain liquid material, you should now create a hollowed solid from the bottle's top face.
392 In Open CASCADE Technology, a hollowed solid is called a *Thick* *Solid* and is internally computed as follows:
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.
398 @figure{/tutorial/images/tutorial_image010.png,"",240}
400 To compute a thick solid, you create an instance of the *BRepOffsetAPI_MakeThickSolid* class by giving the following information:
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.
407 The challenging part in this procedure is to find the face to remove from your shape - the top face of the neck, which:
409 * has a plane (planar surface) as underlying geometry;
410 * is the highest face (in Z coordinates) of the bottle.
412 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.
414 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
415 for(TopExp_Explorer aFaceExplorer(myBody, TopAbs_FACE) ; aFaceExplorer.More() ; aFaceExplorer.Next()){
416 TopoDS_Face aFace = TopoDS::Face(aFaceExplorer.Current());
418 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
420 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:
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.
426 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
427 Handle(Geom_Surface) aSurface = BRep_Tool::Surface(aFace);
428 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
430 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.
431 All objects manipulated by handle, like *Geom_Surface*, inherit from the *Standard_Transient* class which provides two very useful methods concerning types:
433 * *DynamicType* to know the real type of the object
434 * *IsKind* to know if the object inherits from one particular type
436 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.
437 To compare a given type with the type you seek, use the *STANDARD_TYPE* macro, which returns the type of a class:
439 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
440 if(aSurface->DynamicType() == STANDARD_TYPE(Geom_Plane)){
443 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
445 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:
447 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
448 Handle(Geom_Plane) aPlane = Handle(Geom_Plane)::DownCast(aSurface);
449 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
451 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:
453 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
454 TopoDS_Face faceToRemove;
455 Standard_Real zMax = -1;
456 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
458 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:
460 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
461 gp_Pnt aPnt = aPlane->Location();
462 Standard_Real aZ = aPnt.Z();
465 faceToRemove = aFace;
467 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
469 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.
470 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.
471 The collection for shapes can be found in the *TopTools* package. As *BRepOffsetAPI_MakeThickSolid* requires a list, use the *TopTools_ListOfShape* class.
473 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
474 TopTools_ListOfShape facesToRemove;
475 facesToRemove.Append(faceToRemove);
476 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
478 All the necessary data are now available so you can create your hollowed solid by calling the *BRepOffsetAPI_MakeThickSolid* MakeThickSolidByJoin method:
480 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
481 BRepOffsetAPI_MakeThickSolid BodyMaker;
482 BodyMaker.MakeThickSolidByJoin(myBody, facesToRemove, -myThickness / 50, 1.e-3);
483 myBody = BodyMaker.Shape();
484 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
487 @section sec4 Building the Threading
490 @subsection OCCT_TUTORIAL_SUB4_1 Creating Surfaces
493 Up to now, you have learned how to create edges out of 3D curves.
494 You will now learn how to create an edge out of a 2D curve and a surface.
495 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.
496 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:
498 * a coordinate system;
501 Using the same coordinate system *neckAx2* used to position the neck, you create two cylindrical surfaces *Geom_CylindricalSurface* with the following radii:
503 @figure{/tutorial/images/tutorial_image011.png,"",300}
505 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.
507 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
508 Handle(Geom_CylindricalSurface) aCyl1 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 0.99);
510 Handle(Geom_CylindricalSurface) aCyl2 = new Geom_CylindricalSurface(neckAx2, myNeckRadius * 1.05);
511 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
514 @subsection OCCT_TUTORIAL_SUB4_2 Defining 2D Curves
517 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.
518 All geometries defined in the *Geom* package are parameterized. This means that each curve or surface from Geom is computed with a parametric equation.
519 A *Geom_CylindricalSurface* surface is defined with the following parametric equation:
521 P(U, V) = O + R * (cos(U) * xDir + sin(U) * yDir) + V * zDir, where :
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.
528 @figure{/tutorial/images/tutorial_image012.png,"",400}
530 The advantage of having such parameterized geometries is that you can compute, for any (U, V) parameters of the surface:
533 * the derivative vectors of order 1, 2 to N at this point.
535 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:
537 @figure{/tutorial/images/tutorial_image013.png,"",320}
539 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:
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 |
547 The helicoidal curve type is exactly what you need. On the neck's surface, the evolution laws of this curve will be:
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:
552 @figure{/tutorial/images/tutorial_image014.png,"",440}
554 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:
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.
559 @figure{/tutorial/images/tutorial_image015.png,"",440}
561 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:
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.
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
573 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).
575 @figure{/tutorial/images/tutorial_image016.png,"",440}
577 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:
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.
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,
589 Your ellipses are defined as follows:
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
598 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.
599 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.
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
606 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.
607 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.
609 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
610 gp_Pnt2d anEllipsePnt1 = anEllipse1->Value(0);
611 gp_Pnt2d anEllipsePnt2;
612 anEllipse1->D0(M_PI, anEllipsePnt2);
613 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
615 When creating the bottle's profile, you used classes from the *GC* package, providing algorithms to create elementary geometries.
616 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:
618 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
619 Handle(Geom2d_TrimmedCurve) aSegment = GCE2d_MakeSegment(anEllipsePnt1, anEllipsePnt2);
620 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
623 @subsection OCCT_TUTORIAL_SUB4_3 Building Edges and Wires
626 As you did when creating the base profile of the bottle, you can now:
628 * compute the edges of the neck's threading.
629 * compute two wires out of these edges.
631 @figure{/tutorial/images/tutorial_image017.png,"",440}
633 Previously, you have built:
635 * two cylindrical surfaces of the threading
636 * three 2D curves defining the base geometry of the threading
638 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.
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
647 Now, you can create the two profiles of the threading, lying on each surface.
649 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
650 TopoDS_Wire threadingWire1 = BRepBuilderAPI_MakeWire(anEdge1OnSurf1, anEdge2OnSurf1);
651 TopoDS_Wire threadingWire2 = BRepBuilderAPI_MakeWire(anEdge1OnSurf2, anEdge2OnSurf2);
652 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
654 Remember that these wires were built out of a surface and 2D curves.
655 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.
656 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.
658 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
659 BRepLib::BuildCurves3d(threadingWire1);
660 BRepLib::BuildCurves3d(threadingWire2);
661 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
664 @subsection OCCT_TUTORIAL_SUB4_4 Creating Threading
667 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.
668 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.
669 The loft function is implemented in the *BRepOffsetAPI_ThruSections* class, which you use as follows:
671 @figure{/tutorial/images/tutorial_image018.png,"",285}
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.
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
686 @section sec5 Building the Resulting Compound
689 You are almost done building the bottle. Use the *TopoDS_Compound* and *BRep_Builder* classes to build single shape from *myBody* and *myThreading*:
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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
699 Congratulations! Your bottle is complete. Here is the result snapshot of the Tutorial application:
701 @figure{/tutorial/images/tutorial_image019.png,"",320}
703 We hope that this tutorial has provided you with a feel for the industrial strength power of Open CASCADE Technology.
704 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 https://www.opencascade.com/content/technology-support. Our professional services can maximize the power of your Open CASCADE Technology applications.
707 @section sec6 Appendix
710 Complete definition of MakeBottle function (defined in the file src/MakeBottle.cxx of the Tutorial):
712 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
713 TopoDS_Shape MakeBottle(const Standard_Real myWidth, const Standard_Real myHeight,
714 const Standard_Real myThickness)
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);
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);
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);
735 gp_Ax1 xAxis = gp::OX();
738 aTrsf.SetMirror(xAxis);
739 BRepBuilderAPI_Transform aBRepTrsf(aWire, aTrsf);
740 TopoDS_Shape aMirroredShape = aBRepTrsf.Shape();
741 TopoDS_Wire aMirroredWire = TopoDS::Wire(aMirroredShape);
743 BRepBuilderAPI_MakeWire mkWire;
745 mkWire.Add(aMirroredWire);
746 TopoDS_Wire myWireProfile = mkWire.Wire();
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);
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();
763 myBody = mkFillet.Shape();
765 // Body : Add the Neck
766 gp_Pnt neckLocation(0, 0, myHeight);
767 gp_Dir neckAxis = gp::DZ();
768 gp_Ax2 neckAx2(neckLocation, neckAxis);
770 Standard_Real myNeckRadius = myThickness / 4.;
771 Standard_Real myNeckHeight = myHeight / 10.;
773 BRepPrimAPI_MakeCylinder MKCylinder(neckAx2, myNeckRadius, myNeckHeight);
774 TopoDS_Shape myNeck = MKCylinder.Shape();
776 myBody = BRepAlgoAPI_Fuse(myBody, myNeck);
778 // Body : Create a Hollowed Solid
779 TopoDS_Face faceToRemove;
780 Standard_Real zMax = -1;
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();
792 faceToRemove = aFace;
797 TopTools_ListOfShape facesToRemove;
798 facesToRemove.Append(faceToRemove);
799 BRepOffsetAPI_MakeThickSolid BodyMaker;
800 BodyMaker.MakeThickSolidByJoin(myBody, facesToRemove, -myThickness / 50, 1.e-3);
801 myBody = BodyMaker.Shape();
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);
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);
811 Standard_Real aMajor = 2. * M_PI;
812 Standard_Real aMinor = myNeckHeight / 10;
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);
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);
833 BRepOffsetAPI_ThruSections aTool(Standard_True);
834 aTool.AddWire(threadingWire1);
835 aTool.AddWire(threadingWire2);
836 aTool.CheckCompatibility(Standard_False);
838 TopoDS_Shape myThreading = aTool.Shape();
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);
849 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~