CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Sebastien Loriot (GeometryFactory) wrote:
> johnzjq wrote:
> > Dear all,
> >
> > I am using Nef_polyhedron with 
> > Exact_predicates_exact_constructions_kernel.
> > The following assertion was triggered when I was trying to convert a 
> > closed
> > polyhedron to Nef_polyhedron:
> >
> > Error !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > Error !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > CGAL error: assertion violation!
> > Expression : pre_prev->is_border() ||
> > !pe_prev->facet()->plane().is_degenerate()
> > File           : c:\program files
> > (x86)\cgal-3.7\include\cgal\nef_3\polyhedron_3_to_nef_3.h
> > Line          :219
> >
> > The polyhedron is produced with MinkowskiSum and was regularized. I 
> > checked
> > the polyhedron and found one face that caused the assertion. The 
> > vertices of
> > the face is as follows:
> > (which have been convert to double)
> > vertex      x_coord           y_coord         z_coord
> > v1        -18219.3965   -12395.1836   -19974.9375
> > v2        -18185.4824   -12361.2695   -19974.9375
> > v3        -18215.4336   -12391.2207   -19974.9375
> >
> > Questions:
> > 1 Why did this face been judged as "degenerate", especially under an 
> > exact
> > kernal?
> if the points are collinear (I did not check yours), then the plane is 
> degenerate whatever kernel you use.
>
> > 2 Is it proper to depoly simplification to eliminate such kind of face?
> Might be. However Minkowski sum should not produce degenerate faces (if 
> their is no change in the number type used).
>
> If you think this is a bug, please make a bug report as described here:
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/HalfedgeDS_ref/Class_HalfedgeDS_vector.html#Cross_link_anchor_1122 
Sorry for the bad link:
http://www.cgal.org/bug_report.html

> S.
>
> > Any suggestions?
> > Thanks in advance!
> >
> > John