CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Please submit an issue:
https://github.com/CGAL/cgal/issues

Thanks,

Sebastien.

On 10/08/2015 10:54 AM, Taus Møller wrote:
> Maybe a section in the Nef_polyhedron_3 documentation on what kernels
> offer what would be a good idea. Currently there is a little bit on
> the subject, but it is very vague and apparently causes a lot of
> confusion. The first mention of kernels in the documentation for Nef
> polyhedra is in relation to the infimaximal box and here it just
> mentions that an extended kernel is needed to represent unbounded
> polyhedra.
>
> After this the only mention of kernels is in the example section. Here
> it simply states that Cartesian kernels need a FieldNumberType and
> homogeneous kernal need a RingNumberType. If I then click on
> FieldNumberType to find out what it is, it lists a bunch of models
> including several floating point types along with "C++ built-in number
> types ". This leads to the conclusion that i can just use something
> like Cartesian<double>. Only very late is it mentioned that the
> Exact_predicates_exact_constructions_kernel is best suited for use
> with floating point numbers and only in relation to file I/O from OFF
> files. It is not explicitly stated anywhere that all the other kernels
> only work for Nef polyhedra when used with integer types. This is
> extra confusing as Cartesian<double> is otherwise a perfectly valid
> kernel and it only breaks down when used with Nef polyhedra
>
> I realize that this might not cause confusion for experienced users of
> CGAL who are used to working with the kernels and number types of
> CGAL. However, as a new user that picked specifically to use it's 3D
> boolean capabilities this caused quite a bit of problems. Judging from
> the other posts in this thread and elsewhere, I am not the only one
> who have run into this issue.
>
> On 7 October 2015 at 16:58, Sebastien Loriot (GeometryFactory)
> <>
>  wrote:
> > Nef_3 requires a kernel with exact constructions. So usually the best
> > choice is Exact_predicates_exact_constructions_kernel.
> >
> > About the interoperability with Polyhedron_3, the traits class of the
> > polyhedron and of the nef should be the same.
> > If you have a polyhedron using another traits, then you can convert it
> > using for example CGAL/Polyhedron_copy_3.h as follow:
> >
> > Poly2 target;
> > CGAL::Polyhedron_copy_3<Poly1, Poly1::HalfedgeDS> modifier(source);
> > target.delegate(modifier);
> >
> > Sebastien.
> >
> >
> >
> > On 10/07/2015 02:31 PM, Merlin Etzold wrote:
> > > Dear All,
> > >
> > > I am working on the inverted problem of Thiago (I am interested what is
> > > left after to polyhedrons are subtracted form each other)  and have the same
> > > issues as Thiago and Taus. Some clarification would be really great.
> > >
> > > Please keep posting about any insights you may get, I will do the same as
> > > I go along.
> > >
> > > Best wishes,
> > > Merlin :)
> > >
> > > -----Original Message-----
> > > From: 
> > >
> > >  
> > > [mailto:]
> > > On Behalf Of Taus Møller
> > > Sent: 07 October 2015 09:56
> > > To: 
> > >
> > > Subject: Re: [cgal-discuss] Nef_polyhedron and
> > > Exact_predicates_inexact_constructions_kernel
> > >
> > > I have run into the same problem. I have a hard time know what kernel are
> > > usable for what. Even though the exact and inexact construction kernel
> > > models the same concepts, they seem to be different in some ways. I have
> > > found that the Exact_predicates_exact_construction_kernel
> > > works for use with with Nef_polyhedra_3.
> > >
> > > On 2 October 2015 at 18:30, Thiago Milanetto Schlittler
> > > <>
> > >  wrote:
> > > > Hello!
> > > >
> > > >      I’m trying to use Nef polyhedrons to find the intersections between
> > > > polyhedrons, and I’m having some problems. The compiler returns the
> > > > following error when trying to convert a polyhedron to a nef_polyhedron:
> > > >
> > > > In file included from
> > > > /opt/local/include/CGAL/Nef_3/SNC_k3_tree_traits.h:24:
> > > > /opt/local/include/CGAL/Nef_3/Bounding_box_3.h:90:34: error: no member
> > > > named 'lo' in 'CGAL::Box_intersection_d::Box_d<double, 3,
> > > > CGAL::Box_intersection_d::ID_EXPLICIT>'
> > > >         std::copy( q, q + 3, Base::lo );
> > > >
> > > >      I’m using the “Exact_predicates_inexact_constructions_kernel”,
> > > > could this be the reason?
> > > >
> > > > Thanks in advance,
> > > > Thiago Milanetto Schlittler
> > >
> > >
> > >
> > >
> > > --
> > > Regards
> > > Taus Møller
> > > Software Developer, Apiosoft
> > >
> > > --
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