CGAL users discussion list

[Philipp Moeller <>]

<>
 writes:

> Hi!
>
> I have a Polyhedron_3 object and i would like to get the 3 vertex-index of
> facet.
> Basically what i want is a list of indexes which is exactly the same as the 
> 2nd
> part of an .off model. 
>
> How can i do that?
> I tried:
>
> for ( Facet_const_iterator i = Poly.facets_begin(); i != Poly.facets_end();
> ++i)
> {
>     cout << i->plane() << endl;
> }
>
> but it only prints out for zeros a line. 

When using a Polyhedron with indices you need to initialize the indices
manually, e.g.

std::size_t i = 0;
for(Polyhedron::Vertex_iterator it = Poly.vertices_begin(), blabla...)
  it->id() = i++;
i = 0;
for(Polyhedron::Facet_iterator it = Poly.vertices_begin(), blabla...)
  it->id() = i++;
// edges etc.

Then you can iterate around the facets and access the indices:

for(Polyhedron::Face_iterator it = Poly.facets_begin(), blabla...) {
  Polyhedron::Halfedge_around_facet_circulator circ =
    it->facet_begin();
  cout << "Vertex indices of facet: " << it->id();
  do {
    cout << circ->vertex()->id() << " ";
  } while ( ++circ != it->facet_begin());
  cout << '\n';
}

Make sure to use a Polyhedron_item that supports indices. There is one
prepared in CGAL.

#include <CGAL/Polyhedron_items_with_id_3.h>
typedef CGAL::Polyhedron_3<Kernel,CGAL::Polyhedron_items_with_id_3>  
Polyhedron;

But you might need to look-up how to create your own Polyhedron items.

If you really require the order to be the same as in the OFF file you
need to play with Incremental_builder to get the id right when building
the Polyhedron.

>
> Thank you very much in advance!
>
> Sincerely,
>
> Zoli

HTH,
Philipp Moeller
GeometryFactory