CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

As of today, there is no guarantee that the output of the algorithm will 
be free from self-intersection. The algorithm returns a mesh with a
valid graph topology but since points are rounded from an exact
rational representation to a floating point one, it might happen
that some self-intersections are created during the rounding.

The first thing to do it to make sure that if you write the mesh,
you use the highest precision (to avoid another rounding) using
std::setprecision(17) in your stream.

An option to increase the precision of the rounding is to use
an exact vertex point map, and call CGAL::exact() on each
vertex point before doing the rounding (it will increase
the precision but you are still left without guarantees).

We are currently working to avoid the rounding issue but nothing
is ready to be distributed for now.

Sebastien.

On 1/23/20 5:10 PM, slidertom wrote:
> Hello,
> I use
> typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
> typedef CGAL::Surface_mesh<K::Point_3> Surface_mesh;
> from file:
> mesh1.off <http://cgal-discuss.949826.n4.nabble.com/file/t376129/mesh1.off>
> mesh1.off is clipped with plane:
> K::Point_3 plane_pt(0., 2., 0.);
> K::Vector_3 plane_norm(-0.09, 0.09, 0.);
> CGAL::Plane_3<K> plane(plane_pt, plane_norm);
> CGAL::Polygon_mesh_processing::clip(mesh, plane,
> CGAL::Polygon_mesh_processing::parameters::clip_volume(true).use_compact_clipper(true));
> result is:
> mesh2.off <http://cgal-discuss.949826.n4.nabble.com/file/t376129/mesh2.off>
> and
> CGAL::Polygon_mesh_processing::does_self_intersect(mesh);
> -> returns true.
>
> I can not understand, why do I get self intersecting mesh.
> If mesh2.off is exported to the polygon soup and converted back into the
> Surface_mesh -> does_self_intersect returns false in this case -> situation
> is fixed.
>
> Expectation: Polygon_mesh_processing::clip should returned closed, non-self
> intersecting surface.
>
> Maybe I'm doing something wrong?
>
> Tomas
>
>
>
> --
> Sent from: http://cgal-discuss.949826.n4.nabble.com/