CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 04/03/2012 03:02 PM, Oleg wrote:
> Thanks, Sebastien! It works. The only problem is that it's very slow
> and the intersection boundary triangulation is a bit chaotic. What
> would be the best way to check if a point or triangle lies inside a
> polyhedron? Since I've already made the procedure to find two surfaces
> intersection, I'd like to try to make a faster code for two
> polyhedrons union and a better boundary triangulation.
What do you compute exactly as surface intersection? A list of segments?
Is yes, then for each pair of intersecting triangles, an orientation
test around the intersection segment is the only thing you need.

What is your ultimate goal?
If you want to have a faster but less robust union function for two 
polyhedra, we'll probably release such an algorithm in the next release.
You can also have a look at the source code of mepp which has a similar
algorithm.

Sebastien.


> Monday, April 2, 2012, 14:05, you wrote:
>
>  > Since you are using Nef, what about computing the union of the two
>  > spheres and then extract the boundary?
>
>  > N1+=N2;
>  > Polyhedron result;
>  > N1.convert_to_polyhedron(result);
>
>  > see:
>  >
> http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Nef_3_ref/Class_Nef_polyhedron_3.html
>
>  > Sebastien.
>
>
>  > On 04/01/2012 04:13 PM, Oleg wrote:
>  >> Hi all!
>  >>
>  >> Newbie question. I have two triangulated intersecting spheres (3D
>  >> polyhedrons) and want to exclude the triangles from each sphere
> surface that
>  >> are inside the other sphere. What would be the easiest way to do
> that? Here
>  >> is what I'm trying and so far it doesn't work (skipping the unnecessary
>  >> code):
>  >>
>  >> #include<CGAL/Exact_predicates_exact_constructions_kernel.h>
>  >> #include<CGAL/Polyhedron_3.h>
>  >> #include<CGAL/Nef_polyhedron_3.h>
>  >>
>  >> typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
>  >> typedef Kernel::Triangle_3 Triangle;
>  >> typedef CGAL::Polyhedron_3<Kernel> Polyhedron;
>  >> typedef Polyhedron::Facet_const_iterator Facet_const_iterator;
>  >> typedef Nef_polyhedron::Volume_const_handle Volume_const_handle;
>  >>
>  >> std::vector<Triangle> triangles;
>  >>
>  >> //The spheres are represented by two 3D polyhedrons:
>  >>
>  >> Polyhedron P1;
>  >> Polyhedron P2;
>  >> Volume_const_handle v;
>  >>
>  >> //I convert each polyhedron to a nef_polyhedron:
>  >>
>  >> Nef_polyhedron N1(P1);
>  >> Nef_polyhedron N2(P2);
>  >>
>  >> //and check if a vertex from P1 belongs to N2:
>  >>
>  >> for ( Facet_const_iterator i = P1.facets_begin(); i != P1.facets_end();
>  >> ++i){
>  >> if (!assign(v, N2.locate(i->halfedge()->vertex()->point()))&&
>  >> !assign(v, N2.locate(i->halfedge()->next()->vertex()->point()))&&
>  >> !assign(v,
>  >> N2.locate(i->halfedge()->next()->next()->vertex()->point()))) {
>  >> Triangle t(i->halfedge()->vertex()->point(),
>  >> i->halfedge()->next()->vertex()->point(),
>  >> i->halfedge()->next()->next()->vertex()->point());
>  >> triangles.push_back(t);
>  >> }
>  >> }
>  >> //Same for P2
>  >>
>  >> The goal is to have vector 'triangles' with those triangles from each
>  >> surface that are not inside the other sphere. So far it compiles,
> but I get
>  >> empy vector in the output. What do I miss here? Or is there an
> easier way to
>  >> achieve the same goal? Thanks for any help.
>  >>
>  >>
>  >> --
>  >> View this message in context:
> http://cgal-discuss.949826.n4.nabble.com/Determining-if-a-point-is-inside-a-polyhedron-tp4523460p4523460.html
>  >> Sent from the cgal-discuss mailing list archive at Nabble.com.
>
>
>
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> View this message in context: Re[2]: Determining if a point is inside a
> polyhedron
> <http://cgal-discuss.949826.n4.nabble.com/Determining-if-a-point-is-inside-a-polyhedron-tp4523460p4528701.html>
> Sent from the cgal-discuss mailing list archive
> <http://cgal-discuss.949826.n4.nabble.com/> at Nabble.com.