Connecting faces: How declaring shared edges?

I tried the BRepOffsetAPI_MakeFilling fillingMaker;

TopoDS_Edge edge12 = BRepBuilderAPI_MakeEdge(gp_Pnt(10,10,0),gp_Pnt(10,20,0));
TopoDS_Edge edge23 = BRepBuilderAPI_MakeEdge(gp_Pnt(10,20,0),gp_Pnt(20,20,0));
TopoDS_Edge edge36 = BRepBuilderAPI_MakeEdge(gp_Pnt(20,20,0),gp_Pnt(20,10,0));
TopoDS_Edge edge34 = BRepBuilderAPI_MakeEdge(gp_Pnt(20,20,0),gp_Pnt(40,25,10));
TopoDS_Edge edge45 = BRepBuilderAPI_MakeEdge(gp_Pnt(40,25,10),gp_Pnt(40,15,10));
TopoDS_Edge edge56 = BRepBuilderAPI_MakeEdge(gp_Pnt(40,15,10),gp_Pnt(20,10,0));
TopoDS_Edge edge61 = BRepBuilderAPI_MakeEdge(gp_Pnt(20,10,0),gp_Pnt(10,10,0));

fillingMaker.Add(edge12,GeomAbs_C0,Standard_True);
fillingMaker.Add(edge23,GeomAbs_C0,Standard_True);
fillingMaker.Add(edge36,GeomAbs_C0,Standard_False);
fillingMaker.Add(edge34,GeomAbs_C0,Standard_True);
fillingMaker.Add(edge45,GeomAbs_C0,Standard_True);
fillingMaker.Add(edge56,GeomAbs_C0,Standard_True);
fillingMaker.Add(edge61,GeomAbs_C0,Standard_True);

But the produces face (I want a shell) is not what I want->

http://i28.tinypic.com/2uhtkxe.jpg

I need a simple planar surface. Can anybody tell my how I can produce a flat surface with these edges?

Thanks

To have more control, you should use the BRepBuilderAPI_Make* family to create the Vertices, Edges, Wires and Faces. Just be sure to use the same Vertices and Edges when they are indeed, well, the same. Then, you can put all Faces together to form a Shell using BRep_Builder. Sewing is another way to achieve it, but I prefer to have more control on the whole process.

I tried to model my shell from ground up by producing vertices, edges and faces. But if I understand your post, my failure was to not save the shared edges and use them again when I produce the next face?

Thanks a lot!
Simon

Yup. If a Vertex or Edge is in the same position as another one, then you should use the previously created one, otherwise you will obtain Vertices and Edges which are in the same place, yet they are different instances. For them to be shared, they must be the same instance.

Hello Paul!
Thanks for your advice. I have successfully created my desired shell.
And if I call BRepAlgo::IsValid(casShell) is returns true. Very nice.

If I use ShapeAnalysis_Shell to get the free edges 4 edges are displayed (see image). On the other hand, I get strange values from ShapeAnalysis_ShapeContents: NbEdges = 6, NbFreeEdges = 0 ?, NbSharedEdges = 5 ? I expected 4 free edges and 2 shared?

http://i28.tinypic.com/1zczar8.jpg

http://i32.tinypic.com/1040w9j.jpg

my code:

gp_Pnt pointA(100,200,0);
gp_Pnt pointB(200,600,0);
gp_Pnt pointC(200,200,0);
gp_Pnt pointD(300,600,0);

TopoDS_Vertex vertexA = BRepBuilderAPI_MakeVertex(pointA);
TopoDS_Vertex vertexB = BRepBuilderAPI_MakeVertex(pointB);
TopoDS_Vertex vertexC = BRepBuilderAPI_MakeVertex(pointC);
TopoDS_Vertex vertexD = BRepBuilderAPI_MakeVertex(pointD);

TopoDS_Edge edgeAB = BRepBuilderAPI_MakeEdge(vertexA,vertexB);
TopoDS_Edge edgeBC = BRepBuilderAPI_MakeEdge(vertexB,vertexC);
TopoDS_Edge edgeCA = BRepBuilderAPI_MakeEdge(vertexC,vertexA);

TopoDS_Edge edgeBD = BRepBuilderAPI_MakeEdge(vertexB,vertexD);
TopoDS_Edge edgeDC = BRepBuilderAPI_MakeEdge(vertexD,vertexC);

BRepBuilderAPI_MakeWire wireMaker1;

wireMaker1.Add(edgeAB);
wireMaker1.Add(edgeBC);
wireMaker1.Add(edgeCA);
wireMaker1.Build();

TopoDS_Wire wire1 = wireMaker1.Wire();
TopoDS_Face casFace1 = BRepBuilderAPI_MakeFace(wire1,Standard_True);

BRepBuilderAPI_MakeWire wireMaker2;

wireMaker2.Add(edgeBD);
wireMaker2.Add(edgeDC);
wireMaker2.Add(edgeBC);
wireMaker2.Build();

TopoDS_Wire wire2 = wireMaker2.Wire();
TopoDS_Face casFace2 = BRepBuilderAPI_MakeFace(wire2,Standard_False);

BRep_Builder shellMaker;
TopoDS_Shell casShell;
shellMaker.MakeShell(casShell);

shellMaker.Add(casShell,casFace1);
shellMaker.Add(casShell,casFace2);

Standard_Boolean isShapeValid = BRepAlgo::IsValid(casShell); // returns true

TopoDS_Compound freeEdges;
ShapeAnalysis_Shell sas;
sas.CheckOrientedShells(casShell,Standard_True);

if(sas.HasBadEdges()) {
TopoDS_Compound badEdges = sas.BadEdges();
}
if(sas.HasFreeEdges()) {
freeEdges = sas.FreeEdges(); //see image 1, the outer 4 edges (ok)
}

ShapeAnalysis_ShapeContents safc;
safc.Perform(casShell);
int edgeCount = safc.NbEdges(); //6
int freeEdgeCount = safc.NbFreeEdges(); // 0 ?
int sharedEdgeCount = safc.NbSharedEdges(); 5 ?
int sfEdgeCount = safc.NbSharedFreeEdges(); 0

I have no idea what kind of information ShapeAnalysis_ShapeContents actually gathers. There is no documentation about it either. Maybe it's not doing what you expect.

To get information about shared edges I use plain old TopExp::MapShapesAndAncestors. Mapping Edges to Faces is a common choice for me. If you iterate over the container and check the Extent of each list of Faces, you should get the information you want (number of Faces that contain the current Edge).

I will try TopExp::MapShapesAndAncestors. Thanks a lot for your assistance - now I can work on another area of my construction site...

Regards
Simon