CGAL users discussion list

[Manuel Caroli <>]

Hi Thomas,

do you store the facet tags in both incident cells?
facet.first gives you one of the two incident cells, but you don't know 
a priori which one. So either you have to store the information twice or 
you don't only check facet.first but also 
facet.first->neighbor(facet.second) for tags.

Hope this helps

Manuel


Thomas Zangl wrote:
> Manuel Caroli schrieb:
>
> Hi!
>
> > > So, I re-ask, if the following code is correct:
> > After a first glance it looks ok to me. What exactly makes you think 
> > that the output is not correct?
>
> It finds too few incident triangles. I tried something different:
>
> Facet f consists of a three vertices. I can get them like this:
>
> Rt_vertex_handle a = f.first->vertex((f.second + 1) % 4);
> Rt_vertex_handle b = f.first->vertex((f.second + 2) % 4);
> Rt_vertex_handle c = f.first->vertex((f.second + 3) % 4);
>
> and now I iterate over the triangulation:
>
> unsigned int matchedFacets = 0;
> Rt_facet_iterator fIt = t_->facets_begin();
> Rt_facet_iterator fEnd = t_->facets_end();
>
> while (fIt != fEnd) {
>   if (t_->is_infinite(*fIt)) {
>     ++fIt;
>     continue;
>   }
>
>   if (fI->first == f.first && f.second == fIt->second){
>    ++fIt; continue;
>   }
>
>   switch(fIt->first->info().faces[fIt->second]) {
>         case fsUnkown:
>         case fsUnused:
>         case fsSingular:
>           ++fIt;
>           continue;
>           break;
>         default: ; // do nothing
>  }
>
>  bool ma = false;
>  bool mb = false;
>  bool mc = false;
>
>  Rt_vertex_handle fa = fIt->first->vertex((fIt->second + 1) % 4);
>  Rt_vertex_handle fb = fIt->first->vertex((fIt->second + 2) % 4);
>  Rt_vertex_handle fc = fIt->first->vertex((fIt->second + 3) % 4);
>
>  // check which vertices are the same?
>  if ((a == fa) || (a == fb) || (a == fc)) {
>    ma=true;
>  }
>  if ((b == fa) || (b == fb) || (b == fc)) {
>    mb=true;
>  }
>  if ((c == fa) || (c == fb) || (c == fc)) {
>    mc=true;
>  }
>
>  // assert if all 3 vertices match - BUG!
>  assert(!(ma && mb && mc));
>  // now check the flags... at least two TRUE flags are one side
>
>  if (ma && mb) {
>    // side A matched
>   matchedFacets++;
>  }
>  if (mb && mc) {
>    // side B matched
>   matchedFacets++;
>  }
>  if (mc && ma) {
>    // side C matched
>   matchedFacets++;
>  }
>   ++fIt;
> }
>
> Please note, I am at work now and I wrote the code w/o compiling it.
> But I hope it makes the concept clear :-) So, whats the difference? I 
> check if each facet shares 2 vertices with my Facet f. If that is true, 
> they share the same edge. I think thats the same if I say, the facet is 
> incident to f. Right?
>
> I ran the code I posted earlier (with t.incident_facets(..)) and I ran 
> my code above. The number of incident facets is different. The method 
> using t.incident_facets always returnd fewer incident facets than my 
> method.
>
> Any ideas? TIA!