Advice for newbie

Okay, I managed to get past this with the following code:

TopoDS_Shape theBox = BRepPrimAPI_MakeBox(200,40,40);
TopoDS_Shape theSphere = BRepPrimAPI_MakeSphere(gp_Pnt(100,20,20),80);
TopoDS_Shape ShapeCut;
BRepAlgoAPI_Cut aCutOperation(theBox, theSphere);
if (aCutOperation.IsDone()) { // triangulate}

Now I have trouble triangulating.
The code I am using is as follows (which I got from the forum):

ShapeCut = aCutOperation.Shape();
for ( TopExp_Explorer ex( ShapeCut, TopAbs_FACE ) ; ex.More(); ex.Next() )
{
TopoDS_Face F = TopoDS::Face(ex.Current());
// Get triangulation
TopLoc_Location L;
Handle (Poly_Triangulation) facing = BRep_Tool::Triangulation(F,L);
const Poly_Array1OfTriangle & triangles = facing->Triangles();
const TColgp_Array1OfPnt & nodes = facing->Nodes();
for ( int i=triangles.Upper(); i >= triangles.Lower()+1; --i ) // (indeksy 1...N)
{
Poly_Triangle triangle = triangles(i);

Standard_Integer node1,node2,node3;
triangle.Get(node1, node2, node3);

gp_Pnt v1 = nodes(node1);
gp_Pnt v2 = nodes(node2);
gp_Pnt v3 = nodes(node3);
// now we need to transform vertices
// don't forget about face orientation :)
}

I am using my own renderer, so am not using any of open cascade's display functionality. Should I be using another function as well? I read somewhere that I might be able to use BRepMesh::IncrementalMesh, but am not sure how to use it in this setup.

Hi Nick,

could you give us further informations about your problem with triangulation?

Greets,

Commenter-1

Oh, sorry. I wasn't getting any data. I think I figured that out.
My current problem involves getting mesh data from a sphere. What is the best way to do that?
If you know something is a sphere in advance it is pretty easy to triangulate it. However, the method I am using is as follows:

m_shape = BRepPrimAPI_MakeSphere(radius);
BRepMesh::Mesh(m_shape,0.1);
{
PVERTEX V1, V2;
TopExp_Explorer ex;
for ( ex.Init( m_shape, TopAbs_FACE ) ; ex.More(); ex.Next() )
{
TopoDS_Face F = TopoDS::Face(ex.Current());
// Get triangulation
TopLoc_Location L;
Handle (Poly_Triangulation) facing = BRep_Tool::Triangulation(F,L);
const Poly_Array1OfTriangle & triangles = facing->Triangles();
const TColgp_Array1OfPnt & nodes = facing->Nodes();
if (!facing.IsNull())
{
for ( int i=facing->NbTriangles(); i >= 1; --i ) // (indeksy 1...N)
{
Poly_Triangle triangle = triangles(i);

Standard_Integer node1,node2,node3;
triangle.Get(node1, node2, node3);

gp_Pnt v1 = nodes(node1);
gp_Pnt v2 = nodes(node2);
gp_Pnt v3 = nodes(node3);

// do my own render of the circle

The mesh comes out, but it isn't very pretty. Is there a different way to do this if your object is a known primitive like a box or a sphere? If not, what is a good number for getting a decent looking mesh of a sphere, given that I have an idea of how dense I want the polys, and I want the triangles to look better.

Final question is that the line :
if (!facing.IsNull())

fails if the radius is about 1.68 or greater. Not sure why.

Hi Nick,

there are several possibilities to check for known primitives (esp. spheres):
- http://www.opencascade.org/org/forum/thread_9601/ (Shapetype)
- a second possiblity would eb the "canonical recognition" toolkit from OCCT. I think Pavel could give you further informations?

So if you know your shape is a sphere I would triangulate it without OCCs triangulation tools - how to triangulate a sphere shouldn't be a large problem...

Greets,

Commenter-1

I wanted to make sections, but I found the same error Nick Author.
I used the method isdone () but I havn't understand why the section does not made for some shape

hello,
I found the solution.
I have used BRepAlgo_Section instead BRepAlgoAPI_Section

Hi Nick,I am also new here.Sorry if i am not able to help you at this time.:(
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