CGAL users discussion list

["FEYEL Frederic." <>]

First of all, thank you very much for your help. It is a real pleasure
to see this reactivity !

My program is really simple:

  to_cgal(mesh1,P1); to_cgal(mesh2,P2);

  if (!P1.is_closed() || !P2.is_closed() ) ERROR("Supplied meshes are
not closed");

  Nef_polyhedron N1(P1);
  Nef_polyhedron N2(P2);

  Nef_polyhedron N3;

  N3=N1-N2;
  if (!N3.is_simple()) ERROR("Resulting shape is not a 2-manifold");
  N3.convert_to_Polyhedron(P3);

 

The to to_cgal(...) methods allows the conversion from  my own data
structure: it constructs the Polyhedron, knowing the surface mesh,
using the following piece of code:

  Build_poly_from_utility_mesh<HalfedgeDS> builder(mesh);
  P.delegate(builder);


where the Build_poly_from_utility_mesh contains (all UTILITY_xxxxx
classes are my datastructures, containing nodes, elements, etc...
In the test, all those UTILITY_ELEMENT are made of 3-nodes shell elements) :

   void operator()( HDS& hds) {
      CGAL::Polyhedron_incremental_builder_3<HDS> B(hds);

      B.begin_surface(mesh->nodes.size(),mesh->elements.size());

      for (int inode=0;inode<mesh->nodes.size();inode++) {
        VECTOR &pos=mesh->nodes[inode]->position;
        Point p(pos[0],pos[1],pos[2]);
        B.add_vertex(p);
      }

      for (int ielem=0;ielem<mesh->elements.size();ielem++) {
        UTILITY_ELEMENT &an_elem=*mesh->elements[ielem];

        B.begin_facet();
        for (int inode=0;inode<an_elem.nodes.size();inode++)
          B.add_vertex_to_facet(an_elem.nodes[inode]->give_rank());
        B.end_facet();
      }

      B.end_surface();
    }


I think that the creation of the Polyhedron works well, because the VRML
exported file looks ok in an
independent VRML viewer.

Once again, thank you very much for your help.

Frédéric.



Andreas Fabri a écrit :
> Please post your test program if it is short.
>
> andreas
>
> Frédéric FEYEL wrote:
>> Thank you for your advice.
>>
>> I changed my closed surface so that it contains only 3-nodes
>> facets, so that all facets are obviously planar.
>>
>> However, the same problem is still there:
>>
>> CGAL error: assertion violation!
>> Expr: pe_prev->facet()->plane().
>> has_on(pe_prev->opposite()->vertex()->point())
>> File: ./cgal_build/CGAL-3.2.1/include/CGAL/Nef_3/polyhedron_3_to_nef_3.h
>>
>> Does anyone has some extra clues ?
>>
>> Thank you very much for your help,
>>
>> Best Regards,
>>
>> Frederic.
>>
>> Andreas Fabri a écrit :
>>> Hello,
>>>
>>> When you have facets with more than three vertices they must be
>>> coplanar, which might not be given if their coordinates are doubles.
>>> The solution is to either make them coplanar, or to triangulate
>>> the faces.
>>>
>>> best regards,
>>>
>>> andreas
>>>
>>>
>>>
>>>
>>> 
>>>  wrote:
>>>> Hello,
>>>>
>>>> I am very new to CGAL, and I am wondering if it is possible to do
>>>> solid/solid intersections.
>>>>
>>>> It is funny to see that infact, I have the same question as Cedric
>>>> Le Maitre (he sent a mail today)...
>>>>
>>>> More precisely, I have two solids described by two closed Polyhedra
>>>> (using 3 and 4 nodes faces).
>>>>
>>>> I would like to get the Polyhedra that represents the difference
>>>> between
>>>> the two solids.
>>>>
>>>> I tried using the Nef_polyhedron_3 classes :
>>>>
>>>> 1- construct two Polyhedron
>>>> 2- construct the Nef_polyhedron from the 2 polyhedron
>>>> 3- intersect the 2 Nef_polyhedron
>>>> 4- convert the result back to a Polyhedron
>>>>
>>>> When I construct the nef associated with one of the Polyhedrons, I
>>>> get the following error :
>>>>
>>>> CGAL error: assertion violation!
>>>> Expr: pe_prev->facet()->plane().
>>>> has_on(pe_prev->opposite()->vertex()->point())
>>>> File:
>>>> ./cgal_build/CGAL-3.2.1/include/CGAL/Nef_3/polyhedron_3_to_nef_3.h
>>>> Line: 151
>>>>
>>>> I had a look in this file, but the error is not so obvious, at
>>>> least for
>>>> a 'CGAL-beginner' like me.
>>>>
>>>>
>>>> Could anyone guide me, and tell me if such operation is available in
>>>> CGAL, and if yes, how to achieve it ? Any help would be greatly
>>>> appreciated.
>>>>
>>>>
>>>> Best Regards,
>>>>
>>>> Frederic.
>>>>
>>>>
>>>
>>
>>
>>
>>
>