CGAL users discussion list

[Ashwin Nanjappa <>]

On Thu, Jul 16, 2009 at 17:36, Camille 
Wormser<>
 wrote:
> A better way would be to use the do_intersect predicate, because it is exact
> and still efficient, as soon as you are using an
> Exact_predicate_inexact_constructions_kernel. This would mean
>
> 1) checking whether the Triangle_3 and the Segment_3 do intersect or not
> with CGAL::do_intersect
>
> 2) if they do intersect, using CGAL::intersection for the supporting_plane
> of the triangle and the segment. Then you have to deal with the various
> possible results (in particular with an inexact constructions kernel):
[...]
> For (2), either you will use an exact constructions (but slow) kernel, and
> the code will be simple for you to write anyway, or you will use an inexact
> constructions (but fast) kernel, and you will have to choose how to deal
> with the unavoidable robustness issues.
>
> I hope this makes clear why it is much more important to provide the
> do_intersect predicate than the intersection construction for these data
> types.

Thanks Camille, for making it clear. do_intersect() requires only
exact predicates, where as intersection() requires exact constructions
too. I can understand the motive for this API design now.

IAC I use an Exact_predicates_exact_constructions_kernel and was doing
the 2 step process you have detailed above to optimize the result.

~ash