OpenCASCADE BRepTools
Abstract. OpenCASCADE BRepTools provides utilities for BRep data structure. OuterWire method to find the outer wire of a face. Dump method to dump a BRep object. It also can be used as the data exchange for OpenCASCADE native shapes.?
Key Words. OpenCASCADE, BRepTools, BRep, Topology
1. Introduction
OpenCASCADE 提供了一個(gè)類BRepTools,其中有許多static函數(shù),主要用來對(duì)BRep表示的拓樸形狀的數(shù)據(jù)進(jìn)行讀寫,也提供了查找一個(gè)面中外環(huán)(Outer Wire)的函數(shù)。因?yàn)镺penCASCADE中的邊界表示法BRep的數(shù)據(jù)結(jié)構(gòu)如下圖1.1所示:
Figure 1.1 BRep Data Structure of OpenCASCADE
因?yàn)镺penCASCADE中拓樸結(jié)構(gòu)采用了包含關(guān)系,當(dāng)需要將TopoDS_Shape數(shù)據(jù)保存到文件時(shí),如何保持TopoDS_Shape中的關(guān)系,以便于從文件讀取這些數(shù)據(jù)時(shí),可以重構(gòu)出TopoDS_Shape中的各種關(guān)系?
參 考o(jì)pennurbs中的BRep表示時(shí)數(shù)據(jù)的存儲(chǔ)方式,可知直接在BRep中保存拓樸及幾何數(shù)據(jù)的索引,這樣對(duì)數(shù)據(jù)的存儲(chǔ)及讀取時(shí)重構(gòu)拓樸結(jié)構(gòu)還是很方 便的。而在OpenCASCADE中拓樸數(shù)據(jù)是以Handle來保存的,且為組合關(guān)系,即一個(gè)父結(jié)構(gòu)中有一個(gè)列表 (TopoDS_ListOfShape)給包含了子結(jié)構(gòu)數(shù)據(jù)。對(duì)于沒有索引的OpenCASCADE的拓樸結(jié)構(gòu),如何進(jìn)行讀寫操作呢?
本文結(jié)合類BRepTools中的函數(shù),對(duì)OpenCASCADE中TopoDS_Shape數(shù)據(jù)的保存和讀取功能的代碼進(jìn)行分析,從而對(duì)ModelingData中的BRep數(shù)據(jù)做進(jìn)一步的理解。
2.Topology Shape Serialization
OpenCASCADE的類BRepTools中提供了如下函數(shù),可以TopoDS_Shape中的數(shù)據(jù)進(jìn)行導(dǎo)入導(dǎo)出:
v BRepTools::Dump();
v BRepTools::Read();
v BRepTools::Write();
這 幾個(gè)函數(shù)比較常用,因?yàn)榭梢苑奖愕貙opoDS_Shape導(dǎo)出,或?qū)氲絆penCASCADE的Draw Test Harness中,來對(duì)程序一些算法進(jìn)行驗(yàn)證。對(duì)于使用了組合關(guān)系的TopoDS_Shape如何確保數(shù)據(jù)的保存及讀取后,能夠維持這些關(guān)系?帶著這個(gè)問 題去看BRep文件讀寫的功能,應(yīng)該更為清晰。
還是看看代碼,如下所示為輸出TopoDS_Shape的函數(shù),在程序Debug時(shí)比較常用:
// ======================================================================= // function : Dump // purpose : // ======================================================================= void BRepTools::Dump( const TopoDS_Shape& Sh, Standard_OStream& S) { BRepTools_ShapeSet SS; SS.Add(Sh); SS.Dump(Sh,S); SS.Dump(S); }
其中使用了類BRepTools_ShapeSet,這里的Set的意思我理解為集合的意思,其Add函數(shù)如下:
// ======================================================================= // function : Add // purpose : // ======================================================================= Standard_Integer TopTools_ShapeSet::Add( const TopoDS_Shape& S) { if (S.IsNull()) return 0 ; myLocations.Add(S.Location()); TopoDS_Shape S2 = S; S2.Location(TopLoc_Location()); Standard_Integer index = myShapes.FindIndex(S2); if (index == 0 ) { AddGeometry(S2); for (TopoDS_Iterator its(S2,Standard_False,Standard_False); its.More(); its.Next()) Add(its.Value()); index = myShapes.Add(S2); } return index; }
這是一個(gè)遞歸函數(shù),通過AddGeometry函數(shù),將TopoDS_Shape中的幾何信息都保存到相應(yīng)的集合Set中,Set中使用了Map,即給每個(gè)幾何信息一個(gè)唯一的編號(hào)與之對(duì)應(yīng)。
// ======================================================================= // function : AddGeometry // purpose : // ======================================================================= void BRepTools_ShapeSet::AddGeometry( const TopoDS_Shape& S) { // Add the geometry if (S.ShapeType() == TopAbs_VERTEX) { Handle(BRep_TVertex) TV = Handle(BRep_TVertex)::DownCast(S.TShape()); BRep_ListIteratorOfListOfPointRepresentation itrp(TV -> Points()); while (itrp.More()) { const Handle(BRep_PointRepresentation)& PR = itrp.Value(); if (PR-> IsPointOnCurve()) { myCurves.Add(PR -> Curve()); } else if (PR-> IsPointOnCurveOnSurface()) { myCurves2d.Add(PR -> PCurve()); mySurfaces.Add(PR -> Surface()); } else if (PR-> IsPointOnSurface()) { mySurfaces.Add(PR -> Surface()); } ChangeLocations().Add(PR -> Location()); itrp.Next(); } } else if (S.ShapeType() == TopAbs_EDGE) { // Add the curve geometry Handle(BRep_TEdge) TE = Handle(BRep_TEdge)::DownCast(S.TShape()); BRep_ListIteratorOfListOfCurveRepresentation itrc(TE -> Curves()); while (itrc.More()) { const Handle(BRep_CurveRepresentation)& CR = itrc.Value(); if (CR-> IsCurve3D()) { if (!CR-> Curve3D().IsNull()) { myCurves.Add(CR -> Curve3D()); ChangeLocations().Add(CR -> Location()); } } else if (CR-> IsCurveOnSurface()) { mySurfaces.Add(CR -> Surface()); myCurves2d.Add(CR -> PCurve()); ChangeLocations().Add(CR -> Location()); if (CR-> IsCurveOnClosedSurface()) myCurves2d.Add(CR -> PCurve2()); } else if (CR-> IsRegularity()) { mySurfaces.Add(CR -> Surface()); ChangeLocations().Add(CR -> Location()); mySurfaces.Add(CR -> Surface2()); ChangeLocations().Add(CR -> Location2()); } else if (myWithTriangles) { // for XML Persistence if (CR-> IsPolygon3D()) { if (!CR-> Polygon3D().IsNull()) { myPolygons3D.Add(CR -> Polygon3D()); ChangeLocations().Add(CR -> Location()); } } else if (CR-> IsPolygonOnTriangulation()) { myTriangulations.Add(CR -> Triangulation()); myNodes.Add(CR -> PolygonOnTriangulation()); ChangeLocations().Add(CR -> Location()); if (CR-> IsPolygonOnClosedTriangulation()) myNodes.Add(CR -> PolygonOnTriangulation2()); } else if (CR-> IsPolygonOnSurface()) { mySurfaces.Add(CR -> Surface()); myPolygons2D.Add(CR -> Polygon()); ChangeLocations().Add(CR -> Location()); if (CR-> IsPolygonOnClosedSurface()) myPolygons2D.Add(CR -> Polygon2()); } } itrc.Next(); } } else if (S.ShapeType() == TopAbs_FACE) { // Add the surface geometry Handle(BRep_TFace) TF = Handle(BRep_TFace)::DownCast(S.TShape()); if (!TF->Surface().IsNull()) mySurfaces.Add(TF-> Surface()); if (myWithTriangles) { // for XML Persistence Handle(Poly_Triangulation) Tr = TF-> Triangulation(); if (! Tr.IsNull()) myTriangulations.Add(Tr); } ChangeLocations().Add(TF -> Location()); } }
// ======================================================================= // function : WriteGeometry // purpose : // ======================================================================= void BRepTools_ShapeSet::WriteGeometry( const TopoDS_Shape& S, Standard_OStream & OS) const { // Write the geometry if (S.ShapeType() == TopAbs_VERTEX) { // Write the point geometry TopoDS_Vertex V = TopoDS::Vertex(S); OS << BRep_Tool::Tolerance(V) << " \n " ; gp_Pnt p = BRep_Tool::Pnt(V); OS <<p.X()<< " " <<p.Y()<< " " <<p.Z()<< " \n " ; Handle(BRep_TVertex) TV = Handle(BRep_TVertex)::DownCast(S.TShape()); BRep_ListIteratorOfListOfPointRepresentation itrp(TV -> Points()); while (itrp.More()) { const Handle(BRep_PointRepresentation)& PR = itrp.Value(); OS << PR-> Parameter(); if (PR-> IsPointOnCurve()) { OS << " 1 " << myCurves.Index(PR-> Curve()); } else if (PR-> IsPointOnCurveOnSurface()) { OS << " 2 " << myCurves2d.Index(PR-> PCurve()); OS << " " << mySurfaces.Index(PR-> Surface()); } else if (PR-> IsPointOnSurface()) { OS << " 3 " << PR->Parameter2() << " " ; OS << mySurfaces.Index(PR-> Surface()); } OS << " " << Locations().Index(PR-> Location()); OS << " \n " ; itrp.Next(); } OS << " 0 0\n " ; // end representations } else if (S.ShapeType() == TopAbs_EDGE) { // Write the curve geometry Handle(BRep_TEdge) TE = Handle(BRep_TEdge)::DownCast(S.TShape()); OS << " " << TE->Tolerance() << " " ; OS << ((TE->SameParameter()) ? 1 : 0 ) << " " ; OS << ((TE->SameRange()) ? 1 : 0 ) << " " ; OS << ((TE->Degenerated()) ? 1 : 0 ) << " \n " ; Standard_Real first, last; BRep_ListIteratorOfListOfCurveRepresentation itrc = TE-> Curves(); while (itrc.More()) { const Handle(BRep_CurveRepresentation)& CR = itrc.Value(); if (CR-> IsCurve3D()) { if (!CR-> Curve3D().IsNull()) { Handle(BRep_GCurve) GC = Handle(BRep_GCurve)::DownCast(itrc.Value()); GC -> Range(first, last); OS << " 1 " ; // -1- Curve 3D OS << " " <<myCurves.Index(CR-> Curve3D()); OS << " " <<Locations().Index(CR-> Location()); OS << " " <<first<< " " << last; OS << " \n " ; } } else if (CR-> IsCurveOnSurface()) { Handle(BRep_GCurve) GC = Handle(BRep_GCurve)::DownCast(itrc.Value()); GC -> Range(first, last); if (!CR-> IsCurveOnClosedSurface()) OS << " 2 " ; // -2- Curve on surf else OS << " 3 " ; // -3- Curve on closed surf OS << " " <<myCurves2d.Index(CR-> PCurve()); if (CR-> IsCurveOnClosedSurface()) { OS << " " << myCurves2d.Index(CR-> PCurve2()); PrintRegularity(CR -> Continuity(),OS); } OS << " " << mySurfaces.Index(CR-> Surface()); OS << " " << Locations().Index(CR-> Location()); OS << " " <<first<< " " << last; OS << " \n " ; // Write UV Points // for XML Persistence higher performance if (FormatNb() == 2 ) { gp_Pnt2d Pf,Pl; if (CR-> IsCurveOnClosedSurface()) { Handle(BRep_CurveOnClosedSurface) COCS = Handle(BRep_CurveOnClosedSurface)::DownCast(CR); COCS -> UVPoints2(Pf,Pl); } else { Handle(BRep_CurveOnSurface) COS = Handle(BRep_CurveOnSurface)::DownCast(CR); COS -> UVPoints(Pf,Pl); } OS << Pf.X() << " " << Pf.Y() << " " << Pl.X() << " " << Pl.Y() << " \n " ; } } else if (CR-> IsRegularity()) { OS << " 4 " ; // -4- Regularity PrintRegularity(CR-> Continuity(),OS); OS << " " <<mySurfaces.Index(CR-> Surface()); OS << " " <<Locations().Index(CR-> Location()); OS << " " <<mySurfaces.Index(CR-> Surface2()); OS << " " <<Locations().Index(CR-> Location2()); OS << " \n " ; } else if (myWithTriangles) { // for XML Persistence if (CR-> IsPolygon3D()) { Handle(BRep_Polygon3D) GC = Handle(BRep_Polygon3D)::DownCast(itrc.Value()); if (!GC-> Polygon3D().IsNull()) { OS << " 5 " ; // -5- Polygon3D OS << " " <<myPolygons3D.FindIndex(CR-> Polygon3D()); OS << " " <<Locations().Index(CR-> Location()); OS << " \n " ; } } else if (CR-> IsPolygonOnTriangulation()) { Handle(BRep_PolygonOnTriangulation) PT = Handle(BRep_PolygonOnTriangulation)::DownCast(itrc.Value()); if (!CR-> IsPolygonOnClosedTriangulation()) OS << " 6 " ; // -6- Polygon on triangulation else OS << " 7 " ; // -7- Polygon on closed triangulation OS << " " << myNodes.FindIndex(PT-> PolygonOnTriangulation()); if (CR-> IsPolygonOnClosedTriangulation()) { OS << " " << myNodes.FindIndex(PT-> PolygonOnTriangulation2()); } OS << " " << myTriangulations.FindIndex(PT-> Triangulation()); OS << " " <<Locations().Index(CR-> Location()); OS << " \n " ; } } itrc.Next(); } OS << " 0\n " ; // end of the list of representations } else if (S.ShapeType() == TopAbs_FACE) { Handle(BRep_TFace) TF = Handle(BRep_TFace)::DownCast(S.TShape()); const TopoDS_Face& F = TopoDS::Face(S); if (!(TF-> Surface()).IsNull()) { OS << ((BRep_Tool::NaturalRestriction(F)) ? 1 : 0 ); OS << " " ; // Write the surface geometry OS << " " <<TF-> Tolerance(); OS << " " <<mySurfaces.Index(TF-> Surface()); OS << " " <<Locations().Index(TF-> Location()); OS << " \n " ; } else // For correct reading of null face { OS << 0 ; OS << " " ; OS << " " <<TF-> Tolerance(); OS << " " << 0 ; OS << " " << 0 ; OS << " \n " ; } if (myWithTriangles) { // for XML Persistence if (!(TF-> Triangulation()).IsNull()) { OS << 2 ; OS << " " ; // Write the triangulation OS << " " <<myTriangulations.FindIndex(TF-> Triangulation()); } } } }
通過先將幾何數(shù)據(jù)收集到相應(yīng)的集合(映射)中,再在拓樸結(jié)構(gòu)對(duì)應(yīng)的地方以索引號(hào)的方式輸出,這樣就便于從文件讀取數(shù)據(jù)時(shí),以類似的方式來重構(gòu)BRep邊界表示的拓樸Shape的結(jié)構(gòu)。即讀取文件重構(gòu)拓樸結(jié)構(gòu)數(shù)據(jù)是輸出的逆過程。
在實(shí)現(xiàn)從文件讀取BRep表示的數(shù)據(jù)時(shí),先將幾何信息讀取到對(duì)應(yīng)的集合中,再讀取拓樸結(jié)構(gòu)數(shù)據(jù)時(shí),若拓樸結(jié)構(gòu)中包含幾何信息,則以索引的方式,找到對(duì)應(yīng)的幾何數(shù)據(jù)即可。詳細(xì)實(shí)現(xiàn)可參考源程序。
3. For Debugging
由 于BRepTools為Toolkit TKBRep中的類,所以依賴的動(dòng)態(tài)庫(kù)較少,所以在編程時(shí),若要驗(yàn)證一些算法的正確性時(shí),經(jīng)常需要將TopoDS_Shape的數(shù)據(jù)導(dǎo)出,甚至可以直接先 在Draw Test Harness中使用相關(guān)命令來將導(dǎo)出的數(shù)據(jù)導(dǎo)入來查看結(jié)果。
4. Conclusion
通 過BRepTools中對(duì)TopoDS_Shape數(shù)據(jù)的輸出及導(dǎo)入的代碼分析可知,對(duì)于只有組合關(guān)系的數(shù)據(jù),若想維持這種關(guān)系,就需要引入集合映射的類 來產(chǎn)生索引,進(jìn)而在讀取數(shù)據(jù)時(shí),可以根據(jù)索引來重構(gòu)拓樸關(guān)系。由于opennurbs中的BRep在內(nèi)存中本來就是索引的方式,所以在數(shù)據(jù)存取時(shí),實(shí)現(xiàn)要 簡(jiǎn)單很多。
5. References
1. OpenCASCADE Team. BRep Format. 2014.12
2. Shing Liu. Topology and Geometry in OpenCascade-Topology.?
http://www.cppblog.com/eryar/archive/2013/09/21/203338.html
3. Shing Liu. Topology and Geometry in OpenCascade-Vertex
http://www.cppblog.com/eryar/archive/2013/08/20/202678.html
4. Shing Liu. Topology and Geometry in OpenCascade-Edge
http://www.cppblog.com/eryar/archive/2013/08/24/202739.html
5. Shing Liu. Topology and Geometry in OpenCascade-Face
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