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["Sebastien Loriot (GeometryFactory)" <>]

Sebastien Loriot (GeometryFactory) wrote:
> Ben Haller wrote:
> > On Jul 21, 2010, at 10:23 AM, Sebastien Loriot (GeometryFactory) wrote:
> >
> > > Ben Haller wrote:
> > > >  Yeah, I think you're right.  I'm puzzled as to why using exact 
> > > > numbers would solve the problem; the points in question violate the 
> > > > assumption (that 3+ points will not be colinear) even with exact 
> > > > numbers, I would think.  But anyhow, I have come to the conclusion 
> > > > that jittering the points slightly is a reasonable workaround; I 
> > > > often have colinear points, and I don't really care which way the 
> > > > Delaunay triangulation decides to handle them, as long as it picks a 
> > > > way and doesn't raise.  :->
> > > >  Thanks!
> > > The problem here is not which triangulation you will get but
> > > will you get a triangulation. Due to floating point computation,
> > > you end up in a situation (because another predicate was badly
> > > evaluated) where you call a predicate with points that
> > > should form an independent set of points. Unfortunately this is not the
> > > case and the predicate crashes.
> >
> >   I see.  Whereas with exact numbers, the first predicate is evaluated 
> > exactly, and that leads to the avoidance of the second predicate...?  
> > Well, jittering seems to be working for me so far as a workaround, but 
> > if this ever happens to me again, I'll switch to the exact number 
> > type.  Thanks!
> >
> > Ben Haller
> > McGill University
> If no construction are required, an alternative may be
> using Exact_predicates_inexact_constructions_kernel.
which is not working in d-dimension...

sorry, my answer is correct for 2D and 3D only.

> S.
>
> PS: Please answer to the list, the discussion may be useful to other 
> people.