CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

You probably have an face orientation issue.
You can try calling orient_polygon_soup()

http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__repairing__grp.html#gaadc5bac3072b11d2313e40043c729d0a

Note that in case of non-manifold vertices, those will be duplicated.

Sebastien.


On 11/07/2016 10:00 AM, Iason Manolas wrote:
> ah! you are right, it is not valid..
> So probably  there is something wrong with the way i build it?
>
> I use the following code to build it:
>
> using Kernel=CGAL::Exact_predicates_inexact_constructions_kernel;
> using CGALPolyhedron=CGAL::Polyhedron_3<Kernel>;
> using HalfedgeDS=CGALPolyhedron::HalfedgeDS;
>
> template<class HDS>
> class  PolyhedronBuilder:public CGAL::Modifier_base<HDS>
> {
> public:
>
>
>     Mesh         M;
>
>     PolyhedronBuilder(){}
>     explicit PolyhedronBuilder(const Mesh& model):M{model}{}
>     void operator()(HDS& hds)
>     {
>         typedef typename HDS::Vertex    Vertex;
>         typedef typename Vertex::Point     Point;
>
>         CGAL::Polyhedron_incremental_builder_3<HDS> B(hds,true);
>         B.begin_surface(M.vertices.size(),M.indices.size()/3);
>
>         //add vertices
>         for(const auto& vert:M.vertices)
>
> B.add_vertex(Point(vert.Position.x,vert.Position.y,vert.Position.z));
>
>         //add faces
>         for(uint i=0;i<M.indices.size()/3;i+=3)
>         {
>             B.begin_facet();
>             B.add_vertex_to_facet(M.indices[i]);
>             B.add_vertex_to_facet(M.indices[i+1]);
>             B.add_vertex_to_facet(M.indices[i+2]);
>             B.end_facet();
>         }
>         B.end_surface();
>
>     }
> };
>
> and then:
> PolyhedronBuilder<HalfedgeDS> builder(mesh);
> myPolyhedron.delegate(builder);
>
> which was based on
> <http://doc.cgal.org/latest/Polyhedron/classCGAL_1_1Polyhedron__incremental__builder__3.html>
> .
>
>
>
> On 7 November 2016 at 10:24, Sebastien Loriot (GeometryFactory)
> <
>  
> <mailto:>>
>  wrote:
>
>     Could you check P.is_valid() returns true before calling
>     compute_normals?
>
>     On 11/04/2016 03:58 PM, Iason Manolas wrote:
>
>         This
>         <https://github.com/IasonManolas/Thesis/blob/meshScene/mypolyhedron.h
>         
> <https://github.com/IasonManolas/Thesis/blob/meshScene/mypolyhedron.h>>
>         is my code.
>         Do you think there could be something wrong with my cgal
>         distribution?
>
>         Iason
>
>
>         On 4 November 2016 at 16:17, Iason Manolas 
> <
>         
> <mailto:>
>         
> <mailto:
>  
> <mailto:>>>
>  wrote:
>
>
>         
> CGAL::Polyhedron_3<CGAL::Exact_predicates_inexact_constructions_kernel>
>
>             On 4 November 2016 at 16:10, Sebastien Loriot (GeometryFactory)
>             
> <
>  
> <mailto:>
>         
> <mailto:
>  
> <mailto:>>>
>  wrote:
>
>                 What is your polyhedron type?
>
>                 Sebastien.
>
>                 On 11/04/2016 02:59 PM, Iason Manolas wrote:
>
>                     My program crashes when I call compute_vertex_normals.
>                     The stack calling the function that crashes is:
>                     4.In *compute_normal.h*at line 183:
>         *(!is_border**(he,pmesh))*
>                     3.In *helpers.h* at line 45: *face(hd,g)*
>                     2.In *graph_traits_Polyhedron_3.h* at line: 420:
>         *h->face();*
>                     1.In H*alfedgeDS_halfedge_base.h* at line 327:*face()*
>
>                     The error I get in Qt creator is SIGSEGV
>
>         
> <http://stackoverflow.com/questions/2454192/whats-sigsegv-segmentation-fault-in-qt
>         
> <http://stackoverflow.com/questions/2454192/whats-sigsegv-segmentation-fault-in-qt>
>
>         
> <http://stackoverflow.com/questions/2454192/whats-sigsegv-segmentation-fault-in-qt
>         
> <http://stackoverflow.com/questions/2454192/whats-sigsegv-segmentation-fault-in-qt>>>
>                     which after searching found out that propably means:
>         "Trying
>                     to access
>                     pointer with invalid value."
>                     My guess was that I had not correctly initialized the
>                     Polyhedron but
>                     everything seems fine..
>
>                     Any idea why this happens?
>
>                     Best Regards,
>                     Iason Manolas
>
>                     On 1 November 2016 at 10:53, Andreas Fabri
>                     
> <
>         
> <mailto:>
>                     
> <mailto:
>         
> <mailto:>>
>                     
> <mailto:
>         
> <mailto:>
>
>                     
> <mailto:
>         
> <mailto:>>>>
>  wrote:
>
>                         You must
>                         #include <boost/property_map/property_map.hpp>
>
>                         and write
>
>
>         compute_vertex_normals(P,boost::make_assoc_property_map(normals))
>
>
>                         On 01/11/2016 09:45, Iason Manolas wrote:
>
>                             Thanks for your response Sebastien.
>
>                             After reading your code  I wrote:
>                             using
>
>         vd=boost::graph_traits<CGALPolyhedron>::vertex_descriptor;
>                             std::map<vd,Kernel::Vector_3>* normals;
>
>
>         CGAL::Polygon_mesh_processing::compute_vertex_normals(P,normals);
>                     (since
>                             I want to compute vertex and not face normals)
>
>                             But I get:
>
>
>
>         /usr/include/CGAL/Polygon_mesh_processing/compute_normal.h:228:
>                             error:
>                             no matching function for call to
>
>
>         
> ‘put(std::map<CGAL::internal::In_place_list_iterator<CGAL::HalfedgeDS_in_place_list_vertex<CGAL::I_Polyhedron_vertex<CGAL::HalfedgeDS_vertex_base<CGAL::HalfedgeDS_list_types<CGAL::Epick,
>
>
>         CGAL::I_Polyhedron_derived_items_3<CGAL::Polyhedron_items_3>,
>                             std::allocator<int> >, CGAL::Boolean_tag<true>,
>                             CGAL::Point_3<CGAL::Epick> > > >,
>
>
>         
> std::allocator<CGAL::HalfedgeDS_in_place_list_vertex<CGAL::I_Polyhedron_vertex<CGAL::HalfedgeDS_vertex_base<CGAL::HalfedgeDS_list_types<CGAL::Epick,
>
>
>         CGAL::I_Polyhedron_derived_items_3<CGAL::Polyhedron_items_3>,
>                             std::allocator<int> >, CGAL::Boolean_tag<true>,
>                             CGAL::Point_3<CGAL::Epick> > > > > >,
>                             CGAL::Vector_3<CGAL::Epick> >&,
>
>         CGAL::HDS_graph_traits<CGAL::Polyhedron_3<CGAL::Epick>
>
>                                 ::vertex_descriptor&,
>
>
>
>         CGAL::Type_equality_wrapper<CGAL::Cartesian_base_no_ref_count<double,
>                             CGAL::Epick>, CGAL::Epick>::Vector_3&)’
>                                  put(vnm, v, vec);
>                                     ^
>                             That propably means that the put fuction cannot
>                     recognize vnm ( I
>                             passed) as a valid argument?
>
>
>
>                             On 1 November 2016 at 09:50, Sebastien Loriot
>                     (GeometryFactory)
>                             
> <
>         
> <mailto:>
>  
> <mailto:
>         
> <mailto:>>
>                     
> <mailto:
>         
> <mailto:>
>  
> <mailto:
>         
> <mailto:>>>
>                             
> <mailto:
>         
> <mailto:>
>                     
> <mailto:
>         
> <mailto:>>
>  
> <mailto:
>         
> <mailto:>
>                     
> <mailto:
>         
> <mailto:>>>>>
>  wrote:
>
>                                 A writable property map, as describe in the
>                     concept of the
>                             boost web
>                                 site is a mecanism that allow to generically
>                     associate a
>                             property
>                                 (the value type) to a given object (the
>         key).
>
>                                 If you want to associate a normal to a
>         facet of a
>                             Polyhedron, here
>                                 is a simple example (not tested):
>
>
>                                 struct Poly_normal_map{
>
>                                   typedef Polyhedron::Facet_handle key_type;
>                                   typedef Kernel::Vector_3 value_type;
>                                   typedef
>         boost::writable_property_map_tag category;
>
>                                   std::map<Polyhedron::Facet_handle,
>                     Kernel::Vector_3>* normals;
>
>                                   Poly_normal_map() : normals(NULL)
>                                   {}
>
>
>         Poly_normal_map(std::map<Polyhedron::Facet_handle,
>
>          Kernel::Vector_3>& n)
>                                     : normals(*n)
>                                   {}
>
>                                   friend void put(Poly_normal_map pnm,
>
>         Polyhedron::Facet_handle fh,
>                                                   const Kernel::Vector_3& n
>                                   {
>                                     CGAL_assertion(pnm.normals!=0);
>                                     pnm.normals.insert(
>         std::make_pair(fh, n) );
>                                   }
>                                 };
>
>                                 std::map<Polyhedron::Facet_handle,
>                     Kernel::Vector_3> normals;
>                                 Poly_normal_map vpm(normals); //vpm is you
>                     writable property map
>
>
>                                 If you want to make the property map
>         read-write,
>                     you can add
>                                 a get function:
>
>                                   friend const value_type&
>         get(Poly_normal_map pnm,
>
>                      Polyhedron::Facet_handle fh)
>                                   {
>                                     CGAL_assertion(pnm.normals!=0);
>                                     return pnm.normals[fh];
>                                   }
>
>                                 and update the category tag.
>
>                                 Note that the code I've written is roughly
>                     equivalent to using a
>                                 boost::associative_property_map
>
>
>
>         
> (http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>>
>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>>>
>
>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>>
>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/associative_property_map.html>>>>)
>                                 :
>
>                                 std::map<Polyhedron::Facet_handle,
>                     Kernel::Vector_3> normals;
>                                 boost::associative_property_map<
>                                          std::map<Polyhedron::Facet_handle,
>                                                   Kernel::Vector_3> >
>         vpm(normals);
>
>                                 If you're not stuck with Polyhedron_3,
>         you can
>                     use class
>                                 Surface_mesh that comes with its own
>         property
>                     mechanism
>                                 as illustrated in this example:
>
>
>
>
>         
> http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>>
>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>>>
>
>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>>
>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/Polygon_mesh_processing_2compute_normals_example_8cpp-example.html>>>>
>
>                                 Sebastien.
>
>
>
>                                 On 10/31/2016 12:46 PM, Iason Manolas wrote:
>
>                                     Hi,
>
>                                     I am new to CGAL. I have constructed a
>                             CGAL::Polyhedron_3 and
>                                     now I want
>                                     to compute the normal vector for
>         each of its
>                     vertices. So I
>                                     found the
>                                     Polygon Mesh Processing package which
>                     happens to have a
>                             function
>
>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>>
>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>>>
>
>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>>
>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>
>
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e
>         
> <http://doc.cgal.org/latest/Polygon_mesh_processing/group__PMP__normal__grp.html#gad46aaf003999b2939f3f9e4f6fa58d0e>>>>>
>                                     doing exactly what I want . In the above
>                     link I found
>                             out that the
>                                     second argument was of type
>         VertexNormalMap
>                     which is a
>                             model of
>                                     WritablePropertyMap. There was a link
>
>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>>
>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>>>
>
>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>>
>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>
>
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html
>         
> <http://www.boost.org/doc/libs/1_62_0/libs/property_map/doc/WritablePropertyMap.html>>>>>
>                                     to boost libraries explaining(?) what
>                     writable property
>                             map is .
>
>                                     Unfortunately this is my first encounter
>                     with property
>                             maps and
>                                     consequently I am a bit confused..
>                                     I also had a look at cgal's
>         explanation of
>                     property maps
>                             page
>
>                     <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>
>                     <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>>
>
>         <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>
>                     <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>>>
>
>                     <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>
>                     <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>>
>
>         <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>
>                     <http://doc.cgal.org/latest/Property_map/index.html
>         <http://doc.cgal.org/latest/Property_map/index.html>>>> >, but I
>                                     did not
>                                     understand much..
>
>                                     Could anyone suggest a way of
>         creating the
>                     property map
>                             I need?
>
>                                     Best Regards,
>                                     Iason
>
>
>
>                                 --
>                                 You are currently subscribed to
>         cgal-discuss.
>                                 To unsubscribe or access the archives, go to
>
>         https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>
>                     <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>>
>
>         <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>
>                     <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>>>
>
>         <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>
>                     <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>>
>
>         <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>
>                     <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>>>>
>
>
>
>
>                         --
>                         Andreas Fabri, PhD
>                         Chief Officer, GeometryFactory
>                         Editor, The CGAL Project
>
>                         phone: +33.492.954.912 <tel:%2B33.492.954.912>
>         <tel:%2B33.492.954.912>
>                     <tel:%2B33.492.954.912>    skype: andreas.fabri
>
>                         --
>                         You are currently subscribed to cgal-discuss.
>                         To unsubscribe or access the archives, go to
>                         https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>
>                     <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>>
>                         <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>
>                     <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>>>
>
>
>
>
>
>                 --
>                 You are currently subscribed to cgal-discuss.
>                 To unsubscribe or access the archives, go to
>                 https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>
>                 <https://sympa.inria.fr/sympa/info/cgal-discuss
>         <https://sympa.inria.fr/sympa/info/cgal-discuss>>
>
>
>
>
>
>
>     --
>     You are currently subscribed to cgal-discuss.
>     To unsubscribe or access the archives, go to
>     https://sympa.inria.fr/sympa/info/cgal-discuss
>     <https://sympa.inria.fr/sympa/info/cgal-discuss>