CGAL users discussion list

[Thomas Zangl <>]

Hi!

I suspect that I do not use the Facet_Circulator properly.

I want to know for each edge of a RegularTriang. Facet if there is at 
least one neighbour facet. I do it like this:

  unsigned int numOfEdgesWithNeighbours = 0;
  unsigned int faceCounter = 0;
  unsigned int vertices[3];

  vertices[0] = (f.second+1) % 4;
  vertices[1] = (f.second+2) % 4;
  vertices[2] = (f.second+3) % 4;

  for (unsigned int i = 0; i < 3; i++) {
    // faceIndex + 1 = next vertex
    // faceIndex + 2 = next next vertex, forming the edge
    Rt_Facet_circulator fCirc = t_->incident_facets(f.first, vertices[i 
% 3], vertices[(i+1) % 3]);
    Rt_Facet_circulator fCircEnd = fCirc;
    faceCounter = 0;
    do {
      if (t_->is_infinite(*fCirc))
        continue;
      if ((fCirc->first == f.first) && (fCirc->second == f.second)) {
        continue;
      }
      // a neighbour of a cell is every cell, which is not unkown or 
unused or non-singular
      FacetState fState = fCirc->first->info().faces[fCirc->second];
      if ((fState == fsUnkown) or (fState == fsUnused)) {
        fState = 
fCirc->first->neighbor(fCirc->second)->info().faces[fCirc->first->neighbor(fCirc->second)->index(fCirc->first)];
      }
      switch(fState) {
        case fsUnkown:
        case fsUnused:
        case fsSingular:
          continue;
          break;
        default:
          cout << "hasThreeNeighbours: counting as face: " << 
fCirc->first->info().name[fCirc->second] << " state: " << 
fCirc->first->info().toString(fCirc->second) << endl;
          faceCounter++;
      }
    } while(++fCirc!=fCircEnd);

    if (faceCounter > 0) {
      cout << "hasThreeNeighbours: faceCounter=" << faceCounter << endl;
      numOfEdgesWithNeighbours++;
    }
  }
  cout << "hasThreeNeighbours: end. numOfEdgesWithNeighbours = "<< 
numOfEdgesWithNeighbours << endl;

  return (numOfEdgesWithNeighbours == 3) ? true : false;

So, I now have the problem that some faces are counted twice. E.g. if I 
have the edge (2,3) I get the same face as with the edge (0,2). So there 
must be a bug :-)

I also tried some different algo which does a simple vertex_handle 
compare (e.g. iterate over all Rt_Facets of the Reg.Triang unsing the 
finite_facet_iterator, get the 3 edges and compare the vertex handles). 
This works as expected. But its inefficient. So I want to use the 
incident_facets stuff...

Any ideas? TIA!

Thomas