CGAL users discussion list

[Cody Rose <>]

Thank you for your reply. I had not through to use higher levels of 
checking for is_valid. However, I guess I still don't understand what 
those levels do exactly, because when I load the attached simple 
rectangular prism into a Polyhedron_3 and call is_valid(true, 1) then 
the validation still fails, and I cannot see how it could possibly do that.

I discovered this because I still cannot figure out what's actually 
wrong with my original polyhedron - I cannot identify the geometry of 
the dangling face you describe. One OFF viewer I've tried renders two 
dangling faces, but another does not, and when I manually inspect the 
coordinates in the .off they looks fine. I suspect the rendering problem 
has to do with the fact that two of my faces are concave, but I can't 
imagine that CGAL is having a similar issue.

(Incidentally, loading from the .off directly into a Nef_polyhedron 
doesn't help me, because in my actual use case these polyhedrons are 
generated in code, not read from a file.)

Thank you,
Cody

On 3/28/2013 12:41 AM, Sebastien Loriot (GeometryFactory) wrote:
> Hello,
>
> the polygon is actually invalid
> (increase the check level to 3
>     if (!poly.is_valid(false,3)) {
>         std::cout << "poly is invalid\n";
>     }
> ).
>
> You have a dangling face with make the surface non-manifold.
>
> One solution is to use this:
>
>     if (!poly.is_valid(false,3)) {
>               std::cout << "poly is invalid\n";
>               stream.open("poly.off");
>               nef_polyhedron nef;
>               CGAL::OFF_to_nef_3 (stream, nef);
>               std::cout << "created nef\n";
>         }
>
>
> Sebastien.
>
>
> On 03/27/2013 09:28 PM, Cody Rose wrote:
> > Hello,
> >
> > I receive an assertion failure when trying to convert the attached
> > polyhedron to a nef polyhedron. The attached sample code demonstrates my
> > problem. I am running this with CGAL 4.1, Boost 1.47, and LEDA 6.3. I am
> > not sure if there is something about this polyhedron that causes the
> > problem, but I could not find anything in the documentation to help me
> > resolve this issue, and a cursory inspection of the .off doesn't show
> > anything wrong to me (I'm probably just missing something simple).
> >
> > The example program out is as follows:
> >
> > loaded good poly with 16 vertices
> > CGAL error: assertion violation!
> > Expression : pe_prev->is_border() ||
> > internal::Plane_constructor<Plane>::get_plane(pe_prev->facet(),pe_prev->facet()->plane()). 
> >
> > has_on(pe_prev->opposite()->vertex()->point())
> > File : c:\program files
> > (x86)\cgal\include\cgal\nef_3\polyhedron_3_to_nef_3.h
> > Line : 254
> > Explanation:
> > Refer to the bug-reporting instructions at
> > http://www.cgal.org/bug_report.html
> >
> > Thank you,
> > Cody Rose

OFF
8 6 0
200 100 0
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4  0 1 2 3
4  7 6 5 4
4  3 7 4 0
4  0 4 5 1
4  1 5 6 2
4  2 6 7 3