CGAL users discussion list

["Laurent Rineau (GeometryFactory)" <>]

On Tuesday 04 May 2010 14:16:50 Mariette Yvinec wrote:
> 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?

In that case you are right the polyhedral oracle will also produce an 
incorrect result.

But I have checked the data file of Ramin before writing my answer.

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