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[Iason Manolas <>]

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) <> 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) :

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

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>
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>
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 >, 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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