CGAL users discussion list

[Andreas Fabri <>]

Wesley Smith wrote:
> So here's a question.  If I'm iterating over all of the finite cells
> and the reason I'm getting 4 cells instead of 1 for 4 points in a
> triangulation_3 is that the convex hull of the triangulation has faces
> with cells going to the "fictional" infinite point, then shouldn't
> those cells not be accessible via the finite iterator?

I just modified the example file simple.cpp slighlty,
and can't reproduce your finding.

Are you sure to iterator over finite_cells and not over finite_faces,
because for the latter there should be 4.

andreas


#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Triangulation_3.h>

#include <iostream>
#include <fstream>
#include <cassert>
#include <list>
#include <vector>

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;

typedef CGAL::Triangulation_3<K>      Triangulation;

typedef Triangulation::Cell_handle    Cell_handle;
typedef Triangulation::Vertex_handle  Vertex_handle;
typedef Triangulation::Locate_type    Locate_type;
typedef Triangulation::Point          Point;

int main()
{
  // construction from a list of points :
  std::list<Point> L;
  L.push_front(Point(0,0,0));
  L.push_front(Point(1,0,0));
  L.push_front(Point(0,1,0));

  L.push_front(Point(0,0,1));
  Triangulation T(L.begin(), L.end());

  for(Triangulation::Finite_cells_iterator it = T.finite_cells_begin();
      it != T.finite_cells_end();
      ++it){
    std::cout << "oops" << std::endl;
  }

  return 0;
> wes
>
> On 9/14/07, Andreas Fabri 
> <>
>  wrote:
> > Wesley Smith wrote:
> > > > Then you will se that entire R^3 gets triangulated which
> > > > means that there is one additional tetrahedron per face
> > > > of the convex hull that has as fourth vertex the, unique,
> > > > infinite vertex.
> > > Thanks for pointing this out.  I've been reading through the manual
> > > and reference manual quite thoroughly but haven't found a way to
> > > filter these out.  Is there a function such as is_infinite for the
> > > cells?  I don't see anything like this.  I just need a simple test for
> > > this.  Any help is greatly appreciated.
> > ok, so my rtfm doesn't apply here ==:>-
> >
> >
> > As we use derivation, much of the functionality of the Delaunay
> > triangulation is documented in the base class Triangulation_2
> >
> > Go to section "Refines" and click.
> >
> > Note that even this class has a further base class.
> >
> > Some of the documentation is also in the Vertex and Cell class.
> >
> > Also note that there is a user manual which explains things
> > and gives examples, and the reference manual which is just the
> > documentation of the API.
> >
> > best,
> >
> > andreas
> >
> >
> > > thanks,
> > > wes
> > --
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