CGAL users discussion list

[Mariette Yvinec <>]

Le 14/07/12 12:59, Zohar a écrit :

Hi,

Instead of posting a few threads I thought to group my questions into one
thread.
My first two questions please:

	C3t3 c3t3;
	tet_generation(srcPoly, c3t3); // Uses 3D mesh generation where srcPoly is
a polyhedron

	// Triangulation 3
	typedef C3t3::Triangulation Tr3;
	typedef Tr3::Vertex_handle Vertex_handle;
	Tr3& tr = c3t3.triangulation();

	// Add points
        ...
	for ( int i = 0 ; i < nV ; i++ )
		tr.insert(GT::Point_3(V(0,i), V(1,i), V(2,i)));

        // draw tr facets
 	vector<GT::Point_3> points;
 	vector<int> tris;
	int vInd = 0;
	for ( Tr3::Finite_cells_iterator cit = tr.finite_cells_begin() 
		; cit != tr.finite_cells_end() ; cit++ ) {
		for ( int ti = 0 ; ti < 4 ; ti++ ) {
			for ( int i = 0 ; i < 3 ; i++ ) {
				points.push_back(cit->vertex((ti+i)%4)->point());
				tris.push_back(vInd);
				vInd++;
			}
		}
	}
 	MObject omesh = cgal2mesh(points, tris); // draws the facets


1. I just arbitrarily iterated the facets of a cell. How do I iterated them
such that they would have proper orientation (ccw)?

Noway, because there is no "proper" orientation for a facet
in a 3D triangulation

2. I'm working with the triangulation of the mesh generation. I understand
it's Regular_triangulation_3. When I add the new points, I get intersections
by very long faces, while I expected to get a clean delaunay triangulation.
Does the regular triangulation behaves differently (or perhaps I misused the
c3t3)? If it is, is there an easy way to convert it to delaunay?
The mesh generation generates a fine triangulation, and adding the points by
themselves also generates a fine triangulation. It is as if the two are
colliding.

Weights are used to handle sharp 1d feature and sliver exudation.
 If you don't input sharp edges that you want to respect in the mesh
and as long as you don't run the sliver exudation optimization,
all weights are null and
the triangulation is Delaunay.

I don't know what your function tet_generation is doing:
if you  put no criteria on tets,
the mesh generation is in fact generating a surface triangular mesh
with long tets that cross over the objects

Thanks







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-- 
Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis