Calculate vertex normal

LIU's picture
LIU
Wed, 04/30/2008 - 12:00
Forums: 
Other usage issues

Hi, Does anyone know how to calculate vertex normal after triangulation? I have fond that the class BRepMesh_Discret has a function "Normal", does it works?

Any help will be appreciated!! Thanks in advance !!

Yilin

arkoala's picture
arkoala
Wed, 04/30/2008 - 18:05

Take a glance at http://www.opencascade.org/org/forum/thread_13152/

I think it's enough for your needs

LIU's picture
LIU
Tue, 05/06/2008 - 17:13

Thanks for your help!!
I tried to calcule the vertex normal by averaging the normals of the triangles connected to that vertex. But it still has a problem of the normal orientation.

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Handle_Poly_Triangulation l_Triangulation = BRep_Tool::Triangulation(l_Face,l_Location);

if(!l_Triangulation.IsNull())
{
const TColgp_Array1OfPnt& l_Nodes = l_Triangulation->Nodes();

const Poly_Array1OfTriangle& l_Triangles = l_Triangulation->Triangles();

for (int i = 1; i <= l_Nodes.Length(); i++ )
{

gp_XYZ l_VertexNormal(0, 0, 0);

int l_NbTriangles = 0;// number of tiangles sharing current node

for (int j = 1 ; j <= l_Triangles.Length() ; j++)
{

if ( i == l_Triangles.Value(j).Value(1) ||
i == l_Triangles.Value(j).Value(2) ||
i == l_Triangles.Value(j).Value(3) )
{
gp_XYZ l_Pt1 = l_Nodes.Value(l_Triangles.Value(j).Value(1)).XYZ();
gp_XYZ l_Pt2 = l_Nodes.Value(l_Triangles.Value(j).Value(2)).XYZ();
gp_XYZ l_Pt3 = l_Nodes.Value(l_Triangles.Value(j).Value(3)).XYZ();

if (l_Face.Orientation() == TopAbs_REVERSED)
{
gp_XYZ l_V1 = l_pt2 - l_pt3;
gp_XYZ l_V2 = l_pt1 - l_pt2;
}
else
{
gp_XYZ l_V1 = l_pt2 - l_pt1;
gp_XYZ l_V2 = l_pt3 - l_pt2;

}// end else

gp_XYZ l_TriangleNormal = l_V1 ^ l_V2;

if (l_TriangleNormal.SquareModulus() > 0)
{

l_TriangleNormal.Normalize();
l_VertexNormal.Add(l_TriangleNormal);
l_NbTriangles++;
} // end check squaremodules
}// end if (i == l_Triangles.Value(j).Value(1) ...

}// end loop over triangle
l_VertexNormal.Divide(l_NbTriangles);
}// end loop over node

}
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