CGAL users discussion list

[Cornelia Auer <>]

Thank you very much for your response!

However using the CGAL::Exact_predicates_exact_constructions_kernel the 
insertion of segments breaks even earlier. I end up in:

CGAL error: assertion violation!
Expression : !(i>s)
File       : 
c:\Users\bzfauerc\MyAmiraVC9\product\include\arch-Win64VC9\CGAL/In Line 
      : 89
Explanation:  Variable used before being initialized (or CGAL bug)

All I do is:

p1=Point_2(to_exact(myDoublePoint1.x), to_exact(myDoublePoint1.y) );
p2=Point_2(to_exact(myDoublePoint2.x), to_exact(myDoublePoint2.y) );
v_h=sdg.insert(p1,p2, v_h);

I haven't tried the CGAL::Simple_cartesian<CGAL::Gmpq> Kernel yet, as I 
have trouble in my working enviroment to get it properly included.

However if you see something obviously wrong the way I'm proceeding 
above I would be very happy if you let me know. Or could it really be a 
CGAL bug?

Thanks in advance for your answer!
Best,
Cornelia Auer



Am 05.07.2012 07:56, schrieb Sebastien Loriot (GeometryFactory):
> On 07/04/2012 07:46 PM, Cornelia Auer wrote:
> > Dear CGAL users & developers,
> >
> > with the help of the segment_delaunay_graph_2 I try to compute the
> > medial axis for a given *non*-convex polygon.
> > To build the segment delaunay graph (SDG) I am adding edge by edge of
> > the initial polygon. This should give me only weakly intersecting
> > segments.
> >
> > Now, this works perfectly for most of my polygons, however sometimes the
> > construction of the SDG crashes:
> >
> > I try to insert a new segment by
> > v_h=sdg.insert(p1,p2, v_h);
> > however within the insert routine the check SDG.is_valid() fails and the
> > procedure crashes. But for no obvious reason (looking at the polygon).
> > Due to the high grade of templatization the code is really hard to
> > debug/step through for me. I also tried to find the answer by reading
> > the paper of Karavelas, but without success.
> >
> > I would be extremly thankful for any information how degenerate cases
> > (!SDG.is_valid()) arise for weakly intersecting input segments.
> >
> > Or if this could be a numerical issue, as I use the
> > Filtered_kernel<Simple_cartesian<double> >.
> Indeed, you should try with a kernel with exact constructions
> (CGAL::Simple_cartesian<CGAL::Gmpq> or
> CGAL::Exact_predicates_exact_constructions_kernel).
>
> Sebastien.
>
> > Thanks in advance for your help
> > Best,
> > Cornelia Auer