CGAL users discussion list

[Monique Teillaud <>]

Hi,

Let me recall that the infinite vertex is adjacent to each vertex of the 
_convex hull_ of your input points.
So, the fact that you have 2 tetrahedra as input does not imply that you 
have 8 infinite cells in the 3D triangulation of your 8 input points.

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


Le 15/08/11 11:09, henrikz a écrit :
> Using only one tetrahedron I get the numbers you mention:
>
> #vertices: 4 (+ 1)
> #edges   : 10
> #faces   : 10
> #cells   : 5
>
> furthermore I get #cells incident to inf vertex = 4, which makes sense.
>
> Yes, in my previous example I had twice these numbers, BUT STILL the same
>    #cells incident to inf vertex = 4
> which is (probably) my problem.
>
> I was not trying to build one but TWO (disjoint) tetrahedra, so I was
> expecting the number of cells that are connected to the infinite vertex to
> also double!?
>
> Possibly I am using the incremental builder wrong, but it only offers
> /add_vertex/ and /add_cell/ so I don't really believe it.
> Actually I have a very simple reader which just parses the following format
> / Vertices
>   8
>   0 0 0 0
>   1 0 0 0
>   0 1 0 0
>   0 0 1 0
>   2 0 0 0
>   3 0 0 0
>   2 1 0 0
>   2 0 1 0
>   Tetrahedra
>   2
>   1 2 3 4
>   5 6 7 8 /
>
> by first adding 8 vertices and then simply adding 2 cells.
>
> I could restate my questions slightly:  is it true that every boundary face
> of finite tetrahedra are connected to the infinite vertex by a (different)
> infinite cell?
> Because in that case I would expect
>    /VH vh_inf = mesh_.infinite_vertex();
>    std::vector<CH>  inf_cells;
>    mesh_.incident_cells(vh_inf, std::back_inserter(inf_cells) );
>    std::cerr<<  "cells incident to inf vertex "<<  inf_cells.size()<<
> std::endl;
> /
> to yield "8" and NOT "4" for my two disjoint tetrahedra?
>
> Thanks in advance!
>
>
>
> --
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