std::list<CgalPoint> erGeometryExtractConvexPolygon(InputSegmentIterator debut,InputSegmentIterator fin)
{
  CDT cdt ;
  std::list<CgalPoint> result;
  int inc(0);
  for( InputSegmentIterator icg = debut; icg != fin; icg++)
    { //std::cout << inc++ << std::endl;
      cdt.insert_constraint(icg->source(),icg->target());
    };
 
  CDT::Vertex_handle v_inf = cdt.infinite_vertex();
  
  CDT::Face_circulator fc  = cdt.incident_faces(v_inf);
  CDT::Face_circulator fi=fc;
  
  
  CGAL_For_all(fc,fi)
    {
      //std::cout << inc++ << " tour dans cv hull" << std::endl; 
      int id_inf=fc->index(v_inf);
      CDT::Vertex_handle vp = fc->vertex(fc->cw(id_inf));
      result.push_back(vp->point());
    };