CGAL users discussion list

[Mariette Yvinec <>]

Le 16/07/12 11:29, Zohar a écrit :

1. But there is a face orientation for a tet. Thus for example if this
orientation is kept consistently in each tet for the face that consists of
the first three vertices of the tet, then one could represent each of the
four faces with a specific ccw (or cc) orientation:

021, 032, 013, 123.

Meaning if in all the tets the face 021 in each tet (A face which consists
of vertices 0,2,1 of the tet) is ccw wrt the tet then the above ordering
would result in four ccw faces in each tet.

The question is if Triangulation_3 keeps any detail of the vertex ordering
in a tet consistent over the triangulation? I would expect the same behavior
in Triangulation_2 (the order of the vertices in each triangle should be
ccw!) as it holds for a Polyhedron (each face in a poly is ccw).

yes the ordering of the tets are consistent.

2. Thanks for the weights explanation. Here my specific problem was the
hidden vertices in the c3t3 (or the vertices which belong to other
sub-domains than 0, I'm not sure). So treating the c3t3 triangulation as a
normal Triangulation_3 on it own is a mistake. One should iterate the cells
in the 0 sub-domain and construct from them a new Triangulation_3. Then
adding new vertices wouldn't be a problem. I'll publish in a few days a
function that construct a Triangulation_3 from the cells of the zero
sub-domain in a c3t3, I think the examples in the doc should contain
something similar. This would help people understand better the two classes
and how to input / output from them.

Of course you are right that the meshing process does not control
the shape of tets which are
in the triangulation but not in the mesh domain.
Those tets therefore are skiny.


You can't construct a Triangulation_3 form the cells
in a mesh subdomain
because a the finite cells of a CGAL Triangulation_3
cover the whole convex hull of the vertices

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Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis