CGAL users discussion list

[Monique Teillaud <>]

Dear Sybren,

I agree that the sentence that you have included in your email may 
easily be misinterpreted. We should make it more specific.

Thank you for the email.
Best regards,
        Monique Teillaud

Le 23/04/13 08:58, Sybren A. Stüvel a écrit :
> Dear list,
>
> As part of a (for this mailing list not that interesting) algorhtm, I
> have to determine whether two circles intersect. I do this using
> CGAL::do_intersect(...) as described on
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Kernel_23_ref/Function_do_intersect.html
>
> Now I believe that there either is a bug in the implementation, or in
> the documentation, as my interpretation of the latter does not
> correspond to the behaviour of the former. The documentation states that:
>
> /for objects like triangles and polygons that enclose a bounded region,
> this region is part of the object./
>
> This led me to believe that for circles, which also enclose a bounded
> region, this would also apply. I therefore assumed that when one circle
> is embedded in the other (i.e. their boundaries do not intersect),
> CGAL::do_intersect(...) would return true. After all, the bounded
> regions do intersect. However, CGAL behaves differently, and performs
> the intersection test on the boundary alone. I have attached a test
> program that shows this behaviour.
>
> Tested on CGAL 4.1, Windows 8 64-bit, Visual Studio 2010.
>
> I fully understand that a circle is not a disc, and that the behaviour
> of CGAL::do_intersect is perfectly defendable. However, a change in the
> documentation may be a good idea. It would have saved me a few days of
> debugging my code.
>
>
> Kind regards,
> --
> Sybren A. Stüvel
>
> http://stuvel.eu/


--
Monique Teillaud
http://www.inria.fr/sophia/members/Monique.Teillaud/
INRIA Sophia Antipolis - Méditerranée
Institut National de Recherche en Informatique et Automatique