CGAL users discussion list

[Oleg <>]

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.


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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