CGAL users discussion list

[Manuel Caroli <>]

Dear 400555,

400555 wrote:
> Hello !
> Could you please help with my problem.
>
> I make Delaunay_2 for set of points.
>
> Then, on each iteration I change positions of point and accordingly to 
> my criteria do Flip of some edges (only for finite).
> (and I checked that new edge obtained after flipping also stand finite)
Note that as soon as you change point coordinates or do flips manually 
the triangulation is most probably not Delaunay anymore. So there are no 
guarantees anymore about the behavior of e.g. the insert function.
> After somewhile I find that for one edge vertex(i) and vertex which is 
> mirror_vertex to it - become the same.
>
> Do you know how is it possible?
no, because I don't know what your code is doing. You might want to use 
the is_valid() functions from Triangulation_2 and 
Triangulation_data_structure_2 to check whether you still have a valid 
triangulation after each of your modifications.
> There is a part of my code below. ov1 becomes equal to ov2. Someone 
> knows why?
Your code below does not modify the triangulation. I suppose the error 
occurs already during modification. See above.
> Can the fact that I have also square perimeter of vertices (which are 
> lie on the line) be affected to this problem?
I'm sorry I don't understand this one. What do you mean by the square 
perimeter of a vertex?

About your question before about edge with info: As edges are not 
represented explicitly there is no possibility to store some info with 
it. However you could store the info in one of the incident faces, then 
you can look it up in constant time.

best

Manuel

> for (Finite_edges_iterator2 eit = T.finite_edges_begin(); eit != 
> T.finite_edges_end(); ++eit)
> {
>
>      Edge2 ed = *eit;
>
>      Face_handle2 f = ed.first;
>      int i = ed.second;
>      Vertex_handle2 vh1 = f->vertex(T.cw(i));
>      Vertex_handle2 vh2 = f->vertex(T.ccw(i));
>
>      if ((f->vertex(i) != T.infinite_vertex()) && (f->mirror_vertex(i) 
> != T.infinite_vertex()))
>      {
>
>           ov1 = f->vertex(i)->info();
>           ov2 = T.mirror_vertex(f, i)->info();
>
>           - - - - - - 
>
>      }
>
>      - - - - - 
> }
>
> Thank you.