CGAL users discussion list

[Monique Teillaud <>]

mparusinski wrote:
> Hi everyone,

Hi,

> I am performing a 3d mesh triangulation for finite element analysis. In
> order to perform the analysis I need to assign to each facet a corresponding
> boundary pressure information. When doing so I sometimes need to use the
> neighbours of a facets, and by neighbour I understand a facet that share a
> common edge with the one in question.

If you are computing a 3D mesh, you get a partition of some volumes by 
tetrahedra.
In such a 3D structure, there is no reason why there would be a bound on 
the number of tetrahedra (and thus facets) incident to a given edge. You 
can get any number.

> However I run into a problem, I expect
> all facet to have either 0,1,2 or 3 neighbours, since a facet is a triangle
> with 3 edges and I assume surface to be a smooth manifold,

This would indeed be the case if you were meshing a surface (2D object) 
using triangles.

> but I sometimes
> get facets with 4,5 or even 7 facets.

you can get more...

Best,

--
Monique Teillaud
INRIA Sophia Antipolis - Méditerranée
http://www.inria.fr/sophia/members/Monique.Teillaud/