CGAL users discussion list

[Efi Fogel <>]

In some traits there is no kernel, or at least, there is no retation between the point type of the traits and a kernel. BW, a traits defines 3 types:

Point_2,

X_monotone_curve_2, and

Curve_2

The later is defined only by some of the traits, depending on the concept. 

On Sat, Aug 3, 2019, 16:16 Guillaume Damiand <> wrote:

​Thanks for the answers.

Maybe it makes sense, but in the basic viewer, I need a specialized function for each possible type of point in CGAL.

Which types I can use for arrangement ?

Best

Guillaume

Le 30/07/2019 à 14:41, Efi Fogel a écrit :

Without going too deep into the matter, the _expression_

CGAL::Kernel_traits<Arr_circle_segment_traits_2<K>::Point_2>::Kernel

does not make much sense.

Yes, there is a kernel involved, but in general, you do not know how, and in particular, the point type is not Kernel::Point_2.

The same holds for other traits.

In addition, a kernel may have state, so even if you obtain the type, it's not always wise, or even legal, to define a kernel object and use it. It should be up to the user to define and use a kernel.

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On Tue, 30 Jul 2019 at 12:27, Laurent Rineau (CGAL/GeometryFactory) <> wrote:

On Tuesday, July 30, 2019 10:51:37 AM CEST Laurent Rineau (CGAL/
GeometryFactory) wrote:
> On Tuesday, July 30, 2019 9:29:10 AM CEST Guillaume Damiand wrote:
> > Hello;
> >
> > The problem comes from CGAL::Kernel_traits, used to retrieve the kernel
> > given the type of a Point.
> >
> > CGAL::Kernel_traits<Arr_circle_segment_traits_2<K>::Point_2>::Kernel is
> > Dummy_kernel
> >
> > Is it a bug or is it normal ? I would like to obtain K.
>
> That is strange. When `Kernel_traits` return `Dummy_kernel`, that means that
> the type `Point_2` does not a nested `R` type. What is the kernel `K`, in
> your example?

Actually, the issue is that `Arr_circle_segment_traits_2<K>::Point_2` is a
special class `_One_root_point_2<NT, Filter>` defined in `<CGAL/
Arr_geometry_traits/Circle_segment_2.h>` and not related to any kernel.

--

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