CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Hello,

I know nothing about CGAL::Unique_hash_map but from the documention,
http://www.cgal.org/Manual/last/doc_html/cgal_manual/Miscellany_ref/Concept_UniqueHashFunction.html#Cross_link_anchor_2005
you should also provide a functor model of UniqueHashFunction concept.
The only model listed is CGAL::Handle_hash_function (probably the 
default one used in your case).
Again from the doc:
http://www.cgal.org/Manual/last/doc_html/cgal_manual/Miscellany_ref/Class_Handle_hash_function.html#Cross_link_anchor_1997
hash(Handle key) member function doc says:
"returns unique hash value for any Handle  type for which &*key gives a 
unique address."

Which in you case will be incorrect as edges are created on the fly (not 
stored in the Alpha_shape class).

My advice is to either write your own model of UniqueHashFunction for an 
Edge or you can also use a std::map with your own compare function.

Remember that one way to have a unique representation of an
edge is to use a *sorted* pair of Vertex_handle (Vertex_handle pointing 
on edge endpoints).


S.


Song Lin wrote:
> Hi,
>
> I'm trying to mark the edges of an alpha shape using Unique_hash_map.
> Part of my codes are:
>
> typedef Alpha_shape_3::Edge Edge;
> typedef CGAL::Unique_hash_map<Edge,int> UhmEdge2int; << this line is ok
>
> list<Weighted_point> lwp;
> Alpha_shape_3  as(lwp.begin(), lwp.end(), 0, Alpha_shape_3::GENERAL);
>
> Alpha_shape_3::Finite_edges_iterator eit;
> UhmEdge2int uhmedge2int;
>
> for (eit = as.finite_edges_begin(); eit != as.finite_edges_end();eit++)
> {
>         if(as.classify(*eit,0)==Alpha_shape_3::REGULAR)
>         {
>                 uhmedge2int[eit]=1; << there is an error with this line.  
> error: no
> match for ‘operator[]’ in ‘uhmedge2int[eit]’
>         }
> }
>
> I also tried "uhmedge2int[*eit]" and it doesn't work.
>
> But I thought I'm using it as the same way like in the example 51.4.2.
>
> In example 51.4.2: "Example with edges marked as non-removable" a class
> was build like this:
>
> class Constrains_map : public boost::put_get_helper<bool,Constrains_map>
> {
> public:
>
>   typedef boost::readable_property_map_tag                    category;
>   typedef bool                                                value_type;
>   typedef bool                                                reference;
>   typedef boost::graph_traits<Surface const>::edge_descriptor key_type;
>
>   Constrains_map() : mConstrains(false) {}
>
>   reference operator[](key_type const& e) const { return e->is_border() || 
> is_constrained(e) ; }
>   
>   void set_is_constrained ( key_type const& e, bool is )  { mConstrains[e]=is; }
>   
>   bool is_constrained( key_type const& e ) const { return mConstrains.is_defined(e) ? mConstrains[e] : false ; }
>   
> private:
>   
>   CGAL::Unique_hash_map<key_type,bool> mConstrains ;
>   
> };
>
>
> Can anyone tell me what's wrong with my codes?
>
> Best regards,
>
> Lin