CGAL users discussion list

[Mariette Yvinec <>]

Laurent Rineau (GeometryFactory) wrote:

On Monday 03 May 2010 18:43:42 Ramin H wrote:
  

Hi,
I still don't know everything about C3T3 even though I have read the
documentation. In a 3D triangulation, let's say the cell representing a
facet does not belong to domain (subdomain=0). If we find the mirror cell
of this facet, should it belong to the domain (subdomain > 0) ?

To test this idea, I wrote the following code:

  for(Facet_iterator facet_it = c3t3_.facets_begin() ;
      facet_it != c3t3_.facets_end() ;
      ++facet_it)
  {
    Facet facet = *facet_it;
    const Facet f = c3t3_.triangulation().mirror_facet(facet);
    if( (int)(facet.first->subdomain_index()) ==
(int)(f.first->subdomain_index()) )
    {
      std::cerr << "Cell and it's mirror have equal subindex: " <<
(int)(f.first->subdomain_index()) << std::endl;
    }
  }

Here is some sample output:
Cell and it's mirror have equal subindex: 1
Cell and it's mirror have equal subindex: 1
Cell and it's mirror have equal subindex: 0
Cell and it's mirror have equal subindex: 1
Cell and it's mirror have equal subindex: 1
Cell and it's mirror have equal subindex: 1
Cell and it's mirror have equal subindex: 0
Cell and it's mirror have equal subindex: 1

Is this correct behavior? If Facet_iterator is iterating over the facets on
the surface, why a cell representing that facet and it's mirror both can
have subdomain index equal to 1 or 0?
    

No it is not a correct behavior. There is an inconsistency between the answers 
provided by the mesh domain oracle to the two following questions :
  - does a given segment/ray intersects the boundary of the domain,
  - is a given center of cell in the domain or not.

Does your domain class (CGAL::Polyhedral_mesh_domain_3 or something like that) 
use a filtered (exact) kernel or an inexact one?

  

Also what happens if the input polyhedral surface include twice the same
triangle?

-- 
Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis