Deflection and mesher

Wow! That's a lot of faces.

I don't believe that BRepMesh_Discret is no longer supported under OCC 6.3. However, it wasn't very different from FastDiscret. BRepMesh::Mesh simply calls BRepMesh_IncrementalMesh, which calls BRepMesh_FastDiscret. So, don't expect anything different. I believe that BRepMesh_FastDiscret actually uses a delaunay mesher under the covers. So that probably won't help much.

Understand that every face will be meshed. So, I high number of mesh elements is not surprising. If you have a highly contoured surface, 1000 or more triangles is not rediculous, you just have a high number when all the faces are accumulated.

Maybe, you could consider simplifying your geometry (removing small faces, rounds, chamfers, embossments, etc). If you limit the number of faces and the contours of those faces, you could reduce the resulting triangles.

Another option might be to mesh the faces independantly, each with an appropriate deflection. Note, however, that this will remove your smooth transition at the edges between faces.

Finally, you could consider a finite element surface mesher, like netgen, the one on Salome, or the commercial OCC mesher. These would be slower in creating the mesh, but give you more control over what is generated.

Good luck,
Rob

Actually all of Mesher APIs can NOT generate manifold meshes, if there are more than one surface in your IGES file. You can find that the non-manifold will occur at the bounday of adjcent surfaces, i.e. the triangle meshes at the boundary are not cocicident. If there is only one surface in your IGES file, it works well. Below is my sample codes. Hope it makes sense.
-----------------------------------
Bnd_Box myBox;
BRepBndLib::Add (m_topoShape, myBox);

double myDeflection = 0.1;
double myDefAngle = 0.17;
try {BRepMesh_FastDiscret* myMesh =
new BRepMesh_FastDiscret(myDeflection, m_topoShape, myBox, myDefAngle,
Standard_True, Standard_True,Standard_False,Standard_False); // BRepMesh_Discret is Okay as well
}
catch (...) {
BRepMesh_IncrementalMesh(m_topoShape, myDeflection, false, myDefAngle);
}
-----------------------------------

In addition, you can also translate your question to another way:
Step 1. Open your IGES file with OCC
Step 2. Save it with STL format with OCC
Step 3. Then Open the *.stl file

Accordingly, the file is automatically converted into triangle mesh. In this situation, the problem I mentioned above also is inevitable because the Step(2)also implictedly call the mesher APIs in OCC when you investigate the source codes.