CGAL users discussion list

[Andreas Fabri <>]

On 28/02/2012 12:13, Marc Glisse wrote:
> On Mon, 27 Feb 2012, Zohar wrote:
>
> > I read this faq already, and I'm aware that the double is less robust,
> > but I
> > thought that only for complicated algorithm, I need more than it.
>
> Anything that involves computations (like, say, an addition) is
> complicated.
>
> > Frankly I
> > expected the double to be able to intersect two segments with common
> > edge.
> > Otherwise I think this should be emphasized (this specific point
> > regarding
> > intersection) in the intersection / Cartesian / faq (which is too mild
> > IMO
> > on this point).
>
> FAQ: never use Cartesian<double>. If you insist on shooting yourself in
> the foot, at least use Simple_cartesian<double> instead.
>
> > Anyway I tried the exact_exact and it's terribly slow.
>
> There is a price to pay...
>
> If you only need to check whether 2 objects intersect and not know their
> intersection, use a predicate (do_intersect I think) and not a
> construction (intersection?), so the Epick kernel might be enough.


Reality is not black and white, so just using the kernel
which makes exact constructions all the time is not always
the best solution.
The mesh generation algorithms sometimes internally use
an exact kernel, although they round results back to
floating point numbers.

andreas


--
Andreas Fabri, PhD
Chief Officer, GeometryFactory
Editor, The CGAL Project

phone: +33.492.954.912    skype: andreas.fabri