CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Hello,

If I understand correctly what you are trying to do, you are calling
a function which is meant to be used to triangulate a polygon in an
arbitrary plane to fill a hole in a polyhedron, and the boundary of this 
hole is a closed polyline in 3D space (not planar).

Am I correct?

Sebastien.


On 10/18/2013 12:56 PM, Ramón Casero Cañas wrote:
> Hi all,
>
> I have a triangular mesh (attached as x.csv for vertices and tri.csv for
> triangles) with some holes, and I'm using CGAL to fill the holes and
> then triangulate the polygons that cover the holes. To triangulate the
> hole I'm using
>
> CGAL-4.2/demo/Polyhedron/include/CGAL/triangulate_polyhedron.h
>
> This is where the bug is, I believe.
>
> Full code of the program is here
>
> https://code.google.com/p/gerardus/source/browse/trunk/matlab/CgalToolbox/CgalTriFillHoles.cpp
>
> but I highlight the parts of interest.
>
> /* CGAL headers */
> #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
> #include <CGAL/Subdivision_method_3.h>
> #include <CGAL/Polyhedron_3.h>
> #include <CGAL/triangulate_polyhedron.h>
> #include "PolyhedronBuilder.h"
>
> typedef CGAL::Exact_predicates_inexact_constructions_kernel  Kernel;
> typedef CGAL::Polyhedron_3<Kernel>                           Polyhedron;
> typedef CGAL::Point_3<Kernel>                                Point;
> typedef Polyhedron::Facet                                    Facet;
> typedef Polyhedron::Facet_iterator                           Facet_iterator;
> typedef Polyhedron::Vertex_handle                            Vertex_handle;
> typedef Polyhedron::Vertex_iterator
>   Vertex_iterator;
> typedef Polyhedron::Halfedge_around_facet_circulator
> Halfedge_around_facet_circulator;
>
>
> I read the mesh from Matlab into a CGAL::Polyhedron_3
>
>    // polyhedron to contain the input mesh
>    Polyhedron mesh;
>    PolyhedronBuilder<Polyhedron> builder(matlabImport, inTRI, inX);
>    mesh.delegate(builder);
>
> https://code.google.com/p/gerardus/source/browse/trunk/matlab/CgalToolbox/PolyhedronBuilder.h
>
>
> Then the holes get filled with
>
> // sort halfedges such that the non-border edges precede the
> // border edges. We need to do this before any halfedge iterator
> // operations are valid
>    mesh.normalize_border();
>
> // number of holes we have filled
>    mwIndex n =0;
>
> // a closed mesh with no holes will have no border edges. What we do
> // is grab a border halfedge and close the associated hole. This
> // makes the rest of the iterators invalid, so we have to normalize
> // the mesh again. Then we iterate, looking for a new border
> // halfedge, filling the hole, etc.
> //
> // Note that confusingly, mesh.border_halfedges_begin() gives a
> // pointer to the halfedge that is NOT a border in a border
> // edge. The border halfedge is instead
> // mesh.border_halfedges_begin()->opposite()
> while(!mesh.is_closed()){
>
> // exit if user pressed Ctrl+C
>      ctrlcCheckPoint(__FILE__,__LINE__);
>
> // get the first hole we can find, and close it
>      mesh.fill_hole(mesh.border_halfedges_begin()->opposite());
>
> // increase the counter of number of holes we have filled
>      n++;
>
> // renormalize mesh so that halfedge iterators are again valid
>      mesh.normalize_border();
>
> }
>
>
>
> Finally, we want to triangulate all the facets in the mesh, and this is
> where the segfault happens
>
>    // Split all facets to triangles
>    CGAL::triangulate_polyhedron<Polyhedron>(mesh);
>
> This calls the class here
>
> https://code.google.com/p/gerardus/source/browse/trunk/cpp/src/third-party/CGAL-4.2/demo/Polyhedron/include/CGAL/triangulate_polyhedron.h
>
> This is not the main point, but note that I had to change
>
> typedef CGAL::No_intersection_tag                                    Itag;
>
> to
>
> typedef CGAL::Exact_predicates_tag                                   Itag;
>
> Otherwise, I get an error
>
>   sorry, this triangulation does not deal with
>   intersecting constraints
>
> The segfault happens exactly in the "// then modify the polyhedron"
> block. There's a hole with 15 vertices (facet with index 9127) with
> coordinates
>
> 0.015412 0.012213 0.01467
> 0.015387 0.012213 0.01467
> 0.015387 0.012213 0.014646
> 0.015387 0.012213 0.014621
> 0.01493 0.012264 0.014841
> 0.014422 0.012416 0.014914
> 0.014244 0.012467 0.015061
> 0.014219 0.012467 0.015085
> 0.014143 0.012467 0.015134
> 0.01493 0.012289 0.01489
> 0.014981 0.012264 0.01489
> 0.015006 0.012264 0.01489
> 0.015031 0.012264 0.01489
> 0.015057 0.012264 0.01489
> 0.015412 0.012213 0.014694
>
> that has been filled with a polygon, and when the polygon modification
> is in its 18th iteration in the triangulation function, it has acquired
> the vertices:
>
>          const typename CDT::Vertex_handle va = fh->vertex(cdt. cw(index));
>          const typename CDT::Vertex_handle vb = fh->vertex(cdt.ccw(index));
>
> It finds that this is an strictly internal edge, and tries to do
>
>            decorator.set_vertex(h, va->info()->vertex());
>            decorator.set_vertex(h->opposite(), vb->info()->vertex());
>
> However, va->info() == NULL at this point, so va->info()->vertex()
> throws a segfault.
>
>
> Best regards,
>
> Ramon.
>
>
> --
> Dr. Ramón Casero Cañas
>
> Oxford e-Research Centre (OeRC)
> University of Oxford
> 7 Keble Rd
> Oxford OX1 3QG
>
> tlf     +44 (0) 1865 610739
> web http://www.cs.ox.ac.uk/people/Ramon.CaseroCanas
> photos http://www.flickr.com/photos/rcasero/