CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 06/28/2012 05:19 PM, Hugo Mercier wrote:
> Hi all,
>
> I am trying to figure out how to test the intersection (and retrieve the
> result of intersection as a second step) between some primitives and a
> Nef_polyhedron_3.
>
> If I want to test the intersection with a >=2-dimension primitive, I
> think a good way is to build a Polyhedron_3 from that primitive and
> substract it from the Nef_polyhedron.
>
> But what about points and lines ?

You should use this [1] package for that purpose.
The idea is to reduce intersection test at the face level.

(Note that you can use a polyhedron instead of a nef-polyhedron).

You can also test the intersection between two polyhedra with this package.


> About points, there is a locate( Point_3 ) method, but I cannot figure
> out how to know if the resulting volume is the bounded one (my
> nef_polyhedron) or the unbounded "outter" volume (A similar question has
> been asked some time ago on this list without answer).

If you constructed a nef polyhedron, if you call mark() member function
of the volume, true means its in the model.


> About line segments, I cannot rely on the point test, since a line
> segment can intersects a volume, but not its two vertices.
>
> I am currently thinking of converting the Nef_polyhedron to a Polyhedron
> (If I understand correctly, it is done using triangulation underneath,
> right ?) and use intersection tests between Segment_3 and Triangle_3 for
> the "naive" option and AABB trees for something more efficient.
> Is there a more "direct" way to do that with CGAL ?

Sebastien.

[1] 
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Box_intersection_d/Chapter_main.html