CGAL users discussion list

[Andreas Fabri <>]

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
Chief Officer, GeometryFactory
Editor, The CGAL Project

phone: +33.492.954.912    skype: andreas.fabri