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[Iason Manolas <>]

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 HalfedgeDS_halfedge_base.h at line 327: face()

The error I get in Qt creator is SIGSEGV 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 <> 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:>> 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>)
    :

    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>

    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>>
        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>>
        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> >, but I
        did not
        understand much..

        Could anyone suggest a way of creating the property map I need?

        Best Regards,
        Iason



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Andreas Fabri, PhD
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