CGAL users discussion list

[Renato Silveira <>]

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?

Thanks

On Fri, May 22, 2015 at 6:00 AM, Sebastien Loriot (GeometryFactory) <> 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