CGAL users discussion list

[Shuchu Han <>]

Thanks  a lot!   And I have another question :P

Currently, I try to represent several shell structured tetrahedral meshes that has two boundary surface. for example, a thin-wall sphere. 

I am using the incremental build method from the un-documented method described in " CGAL\Triangulation_incremental_builder_3.h"; 

Although it can not pass the "is_valid()" test, it works quite fine. my code can iterative visit the edges, cells and vertices;

however, problems occur recently when i handle a shell structured tetrahedral mesh which has shape edges. specifically, it has two boundaries, and each of them has polycube shape ( i got the surface mesh by polycube mapping).

When my old code iterative visit the finite edges of such a shell tetrahedral mesh, it seems jump into an infinite loop for looking the next edge.  (when use Triangulation_3::Finite_edges_iterator);

Sir,  would u mind to give me an explanation about the theory of Edges of CGAL::Triangulation_3?  or recommend some papers about this.  And Is there any correct method to build a Triangulation_3 from an input file?

Thanks again!

best regards

shuchu

On Tue, Nov 3, 2009 at 4:11 PM, Monique Teillaud <> wrote:

Hi,

If you want your Triangilation_3 to pass the is_valid test, you must create infinite cells as well.
See the User manuel of 3D Triangulations, 1st section, Representation.

You can also simply triangulate the set of points formed by the vertices of the cube, using the insert() method, then the triangulation will be valid.

Shuchu Han wrote:

Hi all,

Can anyone give me some hint about this problem? Thanks a lot !

Currently, I have a cube mesh, which means the elements are hexahedrons.  I wanna tessellate the cube mesh to tetrahedron mesh and represent it by CGAL::Triangulation_3 .  I understand the orientation of a tetrahedron should be positive and the index relationship between neighbor tets. However, still can not get valid Triangulation_3 after try several indexing methods. Especially,  my test program failed at counting the number of finite edges and visit the edges.
  *           *   5----------8
 *   |\         |\
 *   | \        | \
 *   |  \       |  \
 *   |   6----------7
 *   |   |      |   |  *   1---------\4 |  *    \  |       \  |
 *     \ |        \ |
 *      \|         \|
 *       2----------3


My tets:

4 5 2 7      // center one
6 2 5 7      // 6 opposite to 4
2 3 4 7      // 3 opposite to 5
4 7 8 5     // 8 opposite to 2
5 4 2 1     // 1 opposite to 7

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

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