CGAL users discussion list

Hi,

I am currently having a problem computing an intersection of 2 polygons. My 
program stops, and enven with visual debuger, I do not know what happen. My 
current problem stands in a method from a class. Here is the prototype :

void Paving::ComputeCrops( const std::vector< CGAL::Polygon_2<CCd> > 
&polygones )

I previously defined :

typedef CGAL::Cartesian<double> CCd;

Here is the (main) code in my method :

std::vector< CGAL::Polygon_2<CCd> >::const_iterator itb_pol = 
polygones.begin(), ite_pol = polygones.end();
for (;itb_pol!=ite_pol;itb_pol++,cpt++)
{
        CGAL::Polygon_2<CCd> poly_proj;
        CGAL::Polygon_2<CCd>::Vertex_circulator circb = 
(*itb_pol).vertices_circulator(), done = circb;
        do
        {
                TPoint3D <double> p3d = mnt.GetPoint( (*circb).x() , 
(*circb).y() );
                TPoint2D <double> p2d;
                if ( strcmp(m_DEM_type,"ground") == 0 )
                {
                        ori.GroundToPhoto(p3d,p2d);
                }
                else // type = "map"
                {
                        ori.MapToPhoto(p3d,p2d);
                }
                CCd::Point_2 pi(p2d.x,p2d.y);
                poly_proj.push_back( pi );
                } while( (++circb)!=done ) ;

                // on cree le polygone de l'image
                CGAL::Polygon_2<CCd> poly_image;
                {
                        CCd::Point_2 pi0(0.,0.);
                        CCd::Point_2 pi1(ori.GetNs().-1,0.);
                        CCd::Point_2 pi2(ori.GetNs().-1,ori.GetNl()-1.);
                        CCd::Point_2 pi3(0.,ori.GetNl()-1.);
                        poly_image.push_back( pi0 );
                        poly_image.push_back( pi1 );
                        poly_image.push_back( pi2 );
                        poly_image.push_back( pi3 );
                }

                // On fait l'intersection du polygone image et du polygone 
projete
                std::list< Polygon_2_WH_CCd > intR;
                std::list< Polygon_2_WH_CCd >::iterator it;
                
CGAL::intersection(poly_proj,poly_image,std::back_inserter(intR));

/* ... */


I also have defined :

typedef CGAL::Polygon_2<CCd> Polygon_2_CCd;
typedef CGAL::Polygon_with_holes_2<CCd> Polygon_2_WH_CCd;


My programs suddenly stops (sometimes) in the CGAL::intersection(...) 
function. I really do not understand what happen. The both polygons contain 
always 4 points. The debuger did not helped me, that why I write to the list.

Is there any explanation for this behavior ?
Is there any way to test if there is a problem, like a try ... catch 
statement ?

Thanks in advance for your answers.

Olivier Tournaire

PS : I have also tried the same code, remplacing CGAL::intersection(...) with 
CGAL::do_intersect(...). Same result ...