CGAL users discussion list

[Giles Bathgate <>]

This might be relevant:
http://cgal-discuss.949826.n4.nabble.com/Multiple-volumes-Bug-converting-Nef-polyhedron-to-Polyhedron-3-td4658599.html

On 6 June 2014 11:19, GiorgioCGAL 
<>
 wrote:
> Hi,
> I am trying to use CGAL in order to perform the difference of two
> polyhedrons. I work with Polyhedron_3 with the kernel
> CGAL::Simple_cartesian<CGAL::Gmpq> and I convert the polyhedrons to
> Nef_polyhedron_3 for performing the difference operation.
>
> #include <CGAL/Simple_cartesian.h>
> #include <CGAL/Polyhedron_3.h>
> #include <CGAL/Nef_polyhedron_3.h>
> #include <CGAL/Gmpq.h>
> #include <CGAL/Polyhedron_incremental_builder_3.h>
> #include <CGAL/IO/Polyhedron_iostream.h>
>
> typedef CGAL::Simple_cartesian<CGAL::Gmpq> Kernel;
> typedef CGAL::Polyhedron_3<Kernel> Polyhedron;
> typedef CGAL::Nef_polyhedron_3<Kernel> Nef_Polyhedron;
> typedef Polyhedron::HalfedgeDS HalfedgeDS;
>
> Polyhedron diff(Polyhedron & i_poly1, Polyhedron & i_poly2)
> {
>         try
>         {
>                 if (i_poly1.is_closed())
>                 {
>                         Nef_Polyhedron NP1(i_poly1);
>                         Nef_Polyhedron NP2(i_poly2);
>                         Nef_Polyhedron o_NP = NP1 - NP2;
>                         Polyhedron o_poly;
>                         o_NP.convert_to_Polyhedron(o_poly);
>                         return o_poly;
>                 }
>                 else
>                 {
>                         throw Utils::ProcessControl::AREException(
>                                         "At least one geometry is not 
> closed.", __FUNCTION__);
>                 }
>         }
>         catch (Utils::ProcessControl::AREException & exception)
>         {
>                 throw exception;
>         }
> }
>
> It works fine but when I try to perform the difference between A and B and B
> is strictly inside A (generating an holed polyhedron) the orientation of the
> facets of the contour of the hole is not as I would expect.
>
> According to the documentation
> “The convention is that the halfedges are oriented counterclockwise around
> facets as seen from the outside of the polyhedron. An implication is that
> the halfedges are oriented clockwise around the vertices. The notion of the
> solid side of a facet as defined by the halfedge orientation extends to
> polyhedral surfaces with border edges although they do not define a closed
> object. If normal vectors are considered for the facets, normals point
> outwards (following the right-hand rule).”
>
> I would expect that the normal of the facets on the hole of the resulting
> polyhedron (following the right-hand rule) will point to the hole itself but
> they point to the interior of the solid.
> What I am missing? There is a more suitable kernel for working with holed
> polyhedron and that is consistent with the right-hand rule?
>
> Thank you in advance,
> Giorgio
>
>
>
>
> --
> View this message in context: 
> http://cgal-discuss.949826.n4.nabble.com/Polyhedron-3-and-Nef-polyhedron-3-difference-for-holed-polyhedrons-tp4659409.html
> Sent from the cgal-discuss mailing list archive at Nabble.com.
>
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