CGAL users discussion list

[Matthijs Sypkens Smit <>]

On Monday 16 July 2007 16:26, 

 wrote:
> Le Lun 16 juillet 2007 14:27, Matthijs Sypkens Smit a écrit :
> > Exact_predicates_inexact_constructions_kernel I encounter cases where:
> > - coplanar_orientation() returns COLLINEAR, but the construction does
> > not fail and returns a point,
> > - coplanar_orientation() does not return COLLINEAR, but the
> > circumcenter construction does end in an assertion failure.
> >
> > Are both these cases to be expected?
>
> Yes they are: nothing is filtered inside the construction methods.
>
> > In particular the last surprised me,
> > since I was hoping to 'catch' the assertion failure, by testing in
> > advance, but now it seems that this does not generally work.
>
> What you test beforehand with coplanar_orientation is the "exact"
> property of collinearity. The problem is that it has, for example, no
> relation with some double becoming zero in the middle of an inexact
> construction.

Thank you for the explanation. I think I will be able to work with a more 
crude test for co-planarity, that works with a threshold on the distance 
of the 4th point to the plane defined by the three other points (that of 
course must not be collinear :).

>
> >   CGAL error: assertion violation!
> >   Expr: !(i>s)
> >   File: /user/CGAL-3.3/include/CGAL/Interval_nt.h
> >   Line: 77
> >   Explanation: Variable used before being initialized (or CGAL bug)
> > but so far I cannot seem to find the cause of the problem. I do
> > believe that all variables involved have actually been initialized.
>
> This may be the bug that we corrected recently. What exactly did trigger
> this assertion violation? Are you using the Regular Triangulation? If
> you are, the attached diff-file may help you.

I'm using a 3D Delaunay Triangulation. I'm not sure what triggered exactly 
the violation. Since I was just quickly checking to see if it made any 
difference without the intention of actually switching to that kernel, I 
have not bothered to investigate it in more detail.


-- 
Matthijs Sypkens Smit