CGAL users discussion list

["Laurent Rineau (GeometryFactory)" <>]

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?

-- 
Laurent Rineau, PhD
R&D Engineer at GeometryFactory           http://www.geometryfactory.com/
Release Manager of the CGAL Project       http://www.cgal.org/