CGAL users discussion list

[Thomas Zangl <>]

Hi!

Given a regular triangulation in 3d called T. I have a facet of it ("f") 
and now I want to determine if each edge of this facet has at least one 
non-infinite neighbour. This is my code:

bool FacePreProcessor_3::hasThreeNeighbours(Rt_Facet f) {
  cout << "hasThreeNeighbours: begin" << endl;

  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
    cout << "hasThreeNeighbours: v1=" << vertices[i % 3] << " v2=" << 
vertices[(i+1) % 3] << endl;
    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;

      // a neighbour of a cell is every cell, which is not unkown or unused
      switch(fCirc->first->info().faces[fCirc->second]) {
        case fsUnkown:
        case fsUnused:
          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;
}

Just to mention: I use cell_base_with_info to mark some faces as 
"unkown" or "unused" etc. to ignore them in further processing. Ignore 
this part for understanding.

Now I have the following issue: some incident faces are the same of each 
edge. See this debug output:

hasThreeNeighbours: begin
hasThreeNeighbours: v1=1 v2=2
hasThreeNeighbours: counting as face: Face 286 / 0 state: AC or Singular 
(not yet determined)
hasThreeNeighbours: faceCounter=1
hasThreeNeighbours: v1=2 v2=3
hasThreeNeighbours: counting as face: Face 286 / 0 state: AC or Singular 
(not yet determined)
hasThreeNeighbours: faceCounter=1
hasThreeNeighbours: v1=3 v2=1
hasThreeNeighbours: counting as face: Face 286 / 0 state: AC or Singular 
(not yet determined)
hasThreeNeighbours: faceCounter=1
hasThreeNeighbours: end. numOfEdgesWithNeighbours = 3

The face named "Face 286 / 0" (286 is the cell index I gave this cell 
and 0 is the index of the opposite vertex of the cell, JFYI) is strange 
in this example. Its returned by the function "T.incident_facets" as 
being incident to each edge of the given Facet "f". This is obviously wrong.

So, I think I use t.incident_facets wrong :-) Please help!

TIA, Thomas