Split Shape by Plane in OpenCASCADE
Abstract. Sometimes you want to split a shape by plane or even split a shape by a B Spline surface, OpenCASCADE provide a feature class BRepFeat_SplitShape to implement the function. The paper give a sample code to split a cylinder by plane.
Key Words. Split Shape, BRep Feature Algorithms.
1. Introduction
OpenCASCADE提供了Boolean Operation实现了任意两个形状的交、并、差的布尔操作。但是如何实现用一个面将一个形状切割成两半呢?其实Boolean Operation中已经有求交分割的算法,但是没有直接提供一个分割的功能类,而是在BRepFeat_SplitShape提供了分割功能。
Figure 1. Split Cylinder by Plane
2. Code Demo
使用类BRepAlgoAPI_Section和类BRepFeat_SplitShape相结合来实现分割Split形状的功能。完整代码示例如下:
Copyright(C) 2017 Shing Liu([email protected])
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*/
// Visual Studio 2013 & OpenCASCADE7.1.0
#include <gp_Pln.hxx>
#include <TopoDS.hxx>
#include <TopExp.hxx>
#include <TopExp_Explorer.hxx>
#include <BRepTools.hxx>
#include <BRepPrimAPI_MakeCylinder.hxx>
#include <BRepAlgoAPI_Section.hxx>
#include <BRepFeat_SplitShape.hxx>
#pragma comment(lib, "TKernel.lib")
#pragma comment(lib, "TKMath.lib")
#pragma comment(lib, "TKG2d.lib")
#pragma comment(lib, "TKG3d.lib")
#pragma comment(lib, "TKGeomBase.lib")
#pragma comment(lib, "TKGeomAlgo.lib")
#pragma comment(lib, "TKBRep.lib")
#pragma comment(lib, "TKTopAlgo.lib")
#pragma comment(lib, "TKBO.lib")
#pragma comment(lib, "TKPrim.lib")
#pragma comment(lib, "TKFeat.lib")
// ! Test split a cylinder by plane.
// ! You can use the algorithm to split other shapes.
void testSplit()
{
BRepPrimAPI_MakeCylinder aCylinderMaker(10.0, 20.0);
TopoDS_Shape aCylinder = aCylinderMaker.Shape();
// Build section by the split plane for the cylinder.
BRepAlgoAPI_Section aSection(aCylinder, gp_Pln(gp_Pnt(0.0, 0.0, 15.0), gp::DZ()), Standard_False);
aSection.ComputePCurveOn1(Standard_True);
aSection.Approximation(Standard_True);
aSection.Build();
// Split the cylinder shape.
BRepFeat_SplitShape aShapeSpliter(aCylinder);
for (TopExp_Explorer i(aSection.Shape(), TopAbs_EDGE); i.More(); i.Next())
{
TopoDS_Shape anEdge = i.Current();
TopoDS_Shape aFace;
if (aSection.HasAncestorFaceOn1(anEdge, aFace))
{
TopoDS_Edge E = TopoDS::Edge(anEdge);
TopoDS_Face F = TopoDS::Face(aFace);
aShapeSpliter.Add(E, F);
}
}
aShapeSpliter.Build();
// Rebuild left and right shape.
BRep_Builder aBuilder;
TopoDS_Compound aLeftCompound;
TopoDS_Compound aRightCompound;
aBuilder.MakeCompound(aLeftCompound);
aBuilder.MakeCompound(aRightCompound);
// Left shape.
TopTools_MapOfShape aLeftShapeMap;
const TopTools_ListOfShape& aLeftShapes = aShapeSpliter.Left();
for (auto i = aLeftShapes.cbegin(); i != aLeftShapes.cend(); i++)
{
aLeftShapeMap.Add(*i);
aBuilder.Add(aLeftCompound, *i);
}
// Right shape.
TopTools_IndexedMapOfShape aShapeMap;
TopExp::MapShapes(aShapeSpliter.Shape(), TopAbs_FACE, aShapeMap);
for (auto i = aShapeMap.cbegin(); i != aShapeMap.cend(); i++)
{
if (!aLeftShapeMap.Contains(*i))
{
aBuilder.Add(aRightCompound, *i);
}
}
// Output left and right shape.
BRepTools::Write(aLeftCompound, "d:/left.brep");
BRepTools::Write(aRightCompound, "d:/right.brep");
}
int main( int argc, char* argv[])
{
testSplit();
return 0;
}
先创建一个圆柱体,再使用类BRepAlgoAPI_Section将圆柱体用平面进行分割,最后使用类BRepFeat_SplitShape进行分类,得到切割后的形状及Left()形状,把切割后形状中的Left过滤后剩下就是切割另一半的形状;最后导出被平面切割后得到的两半形状。结果用动画演示如下:
![](/qrcode.jpg)
Figure 2. Split Shape animation demo
3. Conclusion
OpenCASCADE提供类BRepFeat_SplitShape来实现对一个形状进行切割的功能,但是要配合BRepAlgoAPI_Section使用。因为Boolean Operation中已经实现了求交、分类的功能,所以在最新版本的源码7.2.0中已经将分割功能集成到了Boolean Operation中。分割后如果没有被改变的面还是原来的面。
转:https://www.cnblogs.com/opencascade/p/SplitShape.html