Sat, 01/10/2009 - 02:50
Forums:
I'm creating a polygon using BRepBuilderAPI_MakePolygon, then using BRepPrimAPI_MakePrism to extrude the polygon to become a 3D shape.
However, the resulting shape isn't being closed.
E.g. if I create the polygon using coordinates in the X-Y plane, then extrude in the Z direction using BRepPrimAPI_MakePrism with the constructor that takes a gp_Vec(0, 0, 1), it creates a shape with the top being the polygon and has sides, but there's no bottom (which should be the same as the top polygon, with reversed Z normals).
Is this expected behavior?
How do you generate the bottom?
Sat, 01/10/2009 - 10:20
Hi Jeff,
You definitively do something wrong. If your base is a face and you are doing a prism out of it, the final solid will be water-proof with top, bottom and lateral faces.
Here is a simple set of commands in DRAW that emulates what you do:
Draw> pload ALL
Draw> polyline p 0 0 0 100 50 0 50 100 0 0 0 0
Draw> mkplane f p 1
Draw> prism pr f 0 0 200
Check the source code of commands (you can get it by calling getsource , e.g. getsource polyline) and compare with your code. Hope you will find a difference somewhere.
Good luck !
Roman
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Sat, 01/31/2009 - 02:29
Roman,
Thanks for you help.
This appears to be a bug in the BRepMesh::Mesh() function.
To make it easier for someone to look into this, what I did was use the code from my previous posting in the TopologyTriangulation project, in the TopologyTriangulationDoc.cpp, in the CTopologyTriangulationDoc::OnVisu() method.
Basically, just create the polygon as mentioned, just before the call to:
BRepMesh::Mesh(ShapeFused,1);
I.e. copy the following code:
BRepBuilderAPI_MakePolygon polygon;
polygon.Add(gp_Pnt(0, 0, 0));
polygon.Add(gp_Pnt(0, 10, 0));
polygon.Add(gp_Pnt(10, 10, 0));
polygon.Add(gp_Pnt(10, 0, 0));
polygon.Close();
TopoDS_Wire wire = polygon.Wire();
TopoDS_Face face = BRepBuilderAPI_MakeFace(wire);
ShapeFused = BRepPrimAPI_MakePrism(face, gp_Vec(0, 0, -1));
BRepMesh::Mesh(ShapeFused,1);
~~~~~~~~~~~~~~~~~
Then run the app and click on the 3rd toolbar button from the left, on the top row (it has a red icon).
If you rotate the box, you'll see that the bottom doesn't have the triangulated faces.
I'd really appreciate if someone looks into this issue.
If there's a way to submit bug reports, I'd be happy to submit this if someone would tell me where to go.
Mon, 01/12/2009 - 09:35
BRepBuilderAPI_MakePolygon creates a wire. Are you creating a face from that wire before calling BRepPrimAPI_MakePrism?
Mon, 01/12/2009 - 18:28
Yes. I'm doing something like the following:
BRepBuilderAPI_MakePolygon polygon;
int numRows = points->GetRowCount();
for (int i = 0; i < numRows; ++i)
{
points->GetElementValue(i, 0, &x);
points->GetElementValue(i, 1, &y);
polygon.Add(gp_Pnt(x, y, 0));
}
polygon.Close();
TopoDS_Face face = BRepBuilderAPI_MakeFace(polygon.Wire());
TopoDS_Shape shape = BRepPrimAPI_MakePrism(face, gp_Vec(0, 0, depth));
Mon, 01/12/2009 - 20:05
One more thing...
After creating the prism, I'm triangulating using:
BRepMesh::Mesh(shape, 1);
I'm then iterating over the triangulated faces and using this information to create a new shape, but it appears that one of the faces is not triangulated.
Using an example project, the following code should demonstrate that the triangulation doesn't include the bottom face:
BRepBuilderAPI_MakePolygon polygon;
polygon.Add(gp_Pnt(0, 0, 0));
polygon.Add(gp_Pnt(0, 10, 0));
polygon.Add(gp_Pnt(10, 10, 0));
polygon.Add(gp_Pnt(10, 0, 0));
polygon.Close();
TopoDS_Wire wire = polygon.Wire();
TopoDS_Face face = BRepBuilderAPI_MakeFace(wire);
TopoDS_Shape prism = BRepPrimAPI_MakePrism(face, gp_Vec(0, 0, -1));
BRepMesh::Mesh(prism, 1);
Handle (AIS_Shape)aSection = new AIS_Shape(prism);
myAISContext->SetDisplayMode(aSection,1);
myAISContext->SetColor(aSection,Quantity_NOC_RED);
myAISContext->SetMaterial(aSection,Graphic3d_NOM_GOLD);
//myAISContext->SetTransparency(aSection,0.1);
myAISContext->Display(aSection);
BRep_Builder builder;
TopoDS_Compound Comp;
builder.MakeCompound(Comp);
for (TopExp_Explorer ex(shape, TopAbs_FACE); ex.More(); ex.Next()) {
TopoDS_Face F = TopoDS::Face(ex.Current());
TopLoc_Location L;
Handle (Poly_Triangulation) facing = BRep_Tool::Triangulation(F,L);
TColgp_Array1OfPnt tab(1,(facing->NbNodes()));
tab = facing->Nodes();
Poly_Array1OfTriangle tri(1,facing->NbTriangles());
tri = facing->Triangles();
for (Standard_Integer i=1;i<=(facing->NbTriangles());i++) {
Poly_Triangle trian = tri.Value(i);
Standard_Integer index1,index2,index3,M,N;
trian.Get(index1,index2,index3);
for (Standard_Integer j=1;j<=3;j++) {
switch (j) {
case 1 :
M = index1;
N = index2;
break;
case 2 :
N = index3;
break;
case 3 :
M = index2;
}
BRepBuilderAPI_MakeEdge ME(tab.Value(M),tab.Value(N));
if (ME.IsDone()) {
builder.Add(Comp,ME.Edge());
}
}
}
}
Handle (AIS_Shape) atriangulation = new AIS_Shape(Comp);
myAISContext->SetDisplayMode(atriangulation,0);
myAISContext->SetColor(atriangulation,Quantity_NOC_WHITE);
myAISContext->Display(atriangulation);
Fit();
Mon, 02/02/2009 - 16:50
Hello Jeff,
if you want to create a face from a planar wire, you should call
TopoDS_Face face = BRepBuilderAPI_MakeFace(wire, Standard_True);
The default argument is Standard_False, which is the cause for your troubles.
Using the planar constructor of MakeFace and then applying it to MakePrism creates a perfect solid. You can check this in the test harness with the 'checkshape' command.
Regards, Kris.
Mon, 02/02/2009 - 19:08
Hi Kris,
Making the change you suggest didn't fix the issue. However, it did make me try passing non default arguments to make the prism and got it working by adding a parameter as follows:
BRepPrimAPI_MakePrism(face, gp_Vec(0, 0, -1), Standard_True);
Thanks for your help!
-Jeff
Fri, 03/20/2020 - 15:09
I know it is an old topic, but to share my experience. I tried to make a cylinder as a solid and then triangulating, one of the face triangles were missing.
The problem is that when get the triangulation, don't use BRepTools::Clean(face).
This causes problems, enumerate the triangulations of all the faces, take the triangles, then clean the faces.
I hope this will help some of the people.