CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 05/22/2015 11:30 AM, Renato Silveira wrote:
> Thank you! I will try it!
> The problem with  CGAL::Exact_predicates_exact_constructions_kernel is
> that the programs consumes all the memory and than crash. The problem
> with points very close to each other can cause this behavior?

Note that there is no _sqrt here (which is not needed for CDT only).

Sebastien.

> Thanks
>
> On Fri, May 22, 2015 at 6:00 AM, Sebastien Loriot (GeometryFactory)
> <
>  
> <mailto:>>
>  wrote:
>
>     It might be that you have two points really close to each other
>     after the self-intersection removal.
>
>     Maybe you should first run the polyline simplification algorithm:
>     
> http://doc.cgal.org/latest/Polyline_simplification_2/index.html#Chapter_2D_Polyline_simplification
>
>     It would definitely help if you can share a minimal example showing
>     the issue.
>
>     For compute_subcurves, you should use
>     CGAL::Exact_predicates_exact_constructions_kernel (EPECK) as Kernel.
>     Note also that you can compute the self-intersection inside a CDT
>     if intersection tag allows it. It will be safer to use EPECK too
>     in this case.
>
>     Sebastien.
>
>
>     On 05/22/2015 09:36 AM, Renato Silveira wrote:
>
>         Hi,
>
>         I'm trying to refine a Deluanay triangulation using
>         CGAL::refine_Delaunay_mesh_2. I'm using the kernel definitions:
>
>         typedef CGAL::Exact_predicates_inexact_constructions_kernelK;
>         typedef CGAL::Triangulation_vertex_base_2<K>Vb;
>         typedef CGAL::Delaunay_mesh_face_base_2<K>Fb;
>         typedef CGAL::Triangulation_data_structure_2<Vb, Fb>Tds;
>         typedef CGAL::Exact_predicates_tagItag;
>         typedef CGAL::Constrained_Delaunay_triangulation_2<K, Tds, Itag>CDT;
>         typedef CGAL::Delaunay_mesh_size_criteria_2<CDT>Criteria;
>         typedef CGAL::Delaunay_mesher_2<CDT, Criteria>Mesher;
>         typedef CDT::Vertex_handleVertex_handle;
>         typedef CDT::PointCDT_Point;
>
>         Initially, my CDT constraints auto-intersects, but I eliminate
>         intersections using *CGAL::compute_subcurves *(using kernel
>         *CGAL::Quotient<CGAL::MP_Float>*) on the constraints before the
>         triangulation, as shown in attached figure (I thought it could
>         solves
>         the problem).
>
>         I got a valid CDT triangulation (as shown in the attached
>         figure) but
>         when I try to refine the CDT, using the method:
>
>         *CGAL::refine_Delaunay_mesh_2(...);*
>
>         with the criteria:
>
>         *Criteria(0.125, 25.0f)*
>
>         I got this assert violation:
>
>         /*terminate called after throwing an instance of
>         'CGAL::Assertion_exception' */
>         /*  what():  CGAL ERROR: assertion violation! */
>         /*Expr: n == zone.fh */
>         /*File: /usr/local/include/CGAL/Mesh_2/Refine_edges.h */
>         /*Line: 438 */
>
>
>         I think constraint intersections can appear again when I convert
>         points
>         from kernel *CGAL::Quotient<CGAL::MP_Float>* to kernel
>         *CGAL::Exact_predicates_inexact_constructions_kernel*. If I
>         could run
>         *CGAL::Delaunay_mesher_2* with kernel
>         *CGAL::Quotient<CGAL::MP_Float>* I
>         will not have any intersections (I think).
>
>         I don't know if the problem is with my constraints or with the
>         mesher.
>         Any ideas what I should try?
>
>         PS:
>         - Using only the boundary as CDT constraints, everything works
>         fine (as
>         shown in attached figure).
>         - I also tested everything with
>         Exact_predicates_exact_constructions_kernel_with_sqrt kernel, with
>         CGAL::Exact_intersections_tag but it takes so much time and then
>         it run
>         out of memory with the message: "GNU MP: Cannot allocate memory
>         (size=25186388)".
>
>
>         Thank you in advance
>
>         Renato
>
>         --
>         */Renato Silveira
>         /*
>                Ph.D. in Computer Science
>                Informatics Institute - UFRGS
>                Porto Alegre - RS - Brazil
>         http://www.inf.ufrgs.br/~rsilveira
>
>
>
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>
>
>
> --
> */Renato Silveira
> /*
>       Ph.D. in Computer Science
>       Informatics Institute - UFRGS
>       Porto Alegre - RS - Brazil
> http://www.inf.ufrgs.br/~rsilveira