CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Martin Baeker wrote:
> Dear all,
>
> I'm getting a bit desperate while trying to work with Polyhedra-stuff.
>
> The manual says that I can access the plane that belongs to a facet with
> Plane_3&         f.plane () if Supports_facet_plane  == CGAL::Tag_true
>
> However, I do not understand how this really works.
>
> When I create a Polyhedron, e.g., with the make_cube_3-routine that is
> provided in the examples, I can access the plane corresponding to each
> facet without problems.
> However, when I write this Polyhedron to an off-file and read it in
> again, I cannot access its planes anymore.
>
> Here is a simple test program to show this:
>
> void do_stuff(Polyhedron & pcube)
> {
>   for (Halfedge_iterator h=pcube.halfedges_begin(); h != 
> pcube.halfedges_end(); ++h)
>     {
>       Facet face=*(h->facet());
>       std::cout << face.plane().orthogonal_vector() << std::endl;
>     }
> }
>
> int main() {
>   Polyhedron pcube;
>   make_cube_3(pcube);
>   std::ofstream os1("poly2.off" ) ;
>   os1 << pcube ;
>   os1.close();
>   do_stuff(pcube);
>   std::cout << "\n";
>   Polyhedron pcube2;
>   std::ifstream is1("poly2.off" ) ;
>   is1 >> pcube2;
>   do_stuff(pcube2);
> }
>
> The output for pcube is correct; for pcube2, all orthogonal vectors are 
> output as 0/1 0/1 0/1.
>
>
> Is there a way to make sure that I can always access the plane
> belonging to a facet? If not, why not? Could I do it by just taking
> three points from the facet and create a plane with them?
>
>
> Any help will be greatly appreciated,
>
> Martin.
>
>
>
>
>
>                    Priv.-Doz. Dr. Martin Bäker
>                    Institut für Werkstoffe
>                    Technische Universität Braunschweig
>                    Langer Kamp 8
>                    38106 Braunschweig
>                    Germany
>                    Tel.: 00-49-531-391-3073
>                    Fax   00-49-531-391-3058
>                    e-mail 
> <>

Can you please post the typedefs as well, so as to make your example 
compilable.


S.