CGAL users discussion list

["Jens K. Becker" <>]

if I use this:

Plane(f1->halfedge()->vertex()->point(),f1->halfedge()->next()->vertex()->point(),f1->halfedge()->prev()->vertex()->point())==Plane(f2->halfedge()->vertex()->point(),f2->halfedge()->next()->vertex()->point(),f2->halfedge()->prev()->vertex()->point())

to check if two facets are in the same plane, it crashes with

CGAL error: precondition violation!
Expr: circulator_size(h->vertex_begin()) >= size_type(3)
while trying to remove a halfedge

(because the facets are not coplanar).

If I use f1->plane()==f2->plane(), it does not crash but does not find any
coplanar facets. Using typedef
CGAL::Exact_predicates_inexact_constructions_kernel K; for both cases.

I also changed the code to test first if they are adjacent and then if 
they are
coplanar, the problem remains...

Something with the plane equations does not work (for me). Does anybody 
have any
other ideas how to check if two facets are coplanar (without using the 
build-in
plane-equation?)?

Thanks for your help,

Jens Becker
--
Dr. J.K. Becker
University of Tuebingen - Institute for Geoscience
Sigwartst. 10 - 72076 Tuebingen (Germany)
Tel.: ++49 7071 29 73139   Fax: +49 7071 5059
web: http://www.jkbecker.de


Quoting Camille Wormser 
<>:

> > I had a code (see below) that
> > does that and it worked nicely using a homogeneous kernel with Gmpz. 
> >  Now I have
> > changed the kernel to be Cartesian<double> and the function does not  work
> > anymore.
>
> I did not read your code in detail, but you say
>
> > I tried different Kernels types (including
> > Exact_predicates_inexact_constructions_kernel) but the problem  remains.
>
> Then it probably means that you are performing some constructions.
>
> I see that you test first "f1->plane()==f2->plane()", and then "f2- 
> >halfedge()->next()->opposite()->facet()==f1".
>
> So the supporting planes are constructed before being compared. You  
> can avoid this construction by first testing that the two faces are  
> adjacent, and then checking whether the four vertices are coplanar or 
>  not.
>
> This may solve your problem, if you use  
> Exact_predicates_inexact_constructions_kernel again.
> --
> Camille
>
> --
> You are currently subscribed to cgal-discuss.
> To unsubscribe or access the archives, go to
> https://lists-sop.inria.fr/wws/info/cgal-discuss