CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

On 04/23/2015 02:32 PM, Malcolm Mielle wrote:
> Hello,
>
> I'm new to CGAL so please bear with me.
>
> I'm trying to understand how to compute the Voronoi line of an image I
> have. I have read those two user manuals :
> http://doc.cgal.org/latest/Segment_Delaunay_graph_2/index.html#Chapter_2D_Segment_Delaunay_Graphs
> and
> http://doc.cgal.org/latest/Voronoi_diagram_2/index.html#Chapter_2D_Voronoi_Diagram_Adaptor
> but some stuff are still very unclear to me.
>
> In the example, the "sites" (which if I understand correctly are the
> points and line of my image) are inserted through  :
>
> SDG2          sdg;
> SDG2::Site_2  site;
> while ( ifs >> site ) { sdg.insert( site ); }
> ifs.close();
>
> But what is the structure of the sites ? This example assume I have a
> file containing site but I don't understand how to create them :s.

A site is either a point or a segment. The stream format is the following:
s x1 y1 x2 y2 # segment define by the points (x1,y1) and (x2,y2)
p x3 y3  # point (x3,y3)
....


> Also, if I want to obtain the voronoi line as a graph of points, am I
> better using the Adaptor or the Segment Delaunay Graphs ? The difference
> between the two is still unclear to me.

?
I guess you want to get the voronoi diagram bisectors of a set of
segments approximated by a set of points.
In that case the easiest way is to use the draw_dual method [1]

A possible implementation of Stream is:
    struct Toto{
      std::list<Ray_2> ray_list;
      std::list<Line_2> line_list;
      std::list<Segment_2> seg_list;

      void operator<<(const Ray_2& p){ray_list.push_back(p);}
      void operator<<(const Line_2& p){line_list.push_back(p);}
      void operator<<(const Segment_2& p){seg_list.push_back(p);}
    };

Sebastien.

[1] 
http://doc.cgal.org/latest/Segment_Delaunay_graph_2/classCGAL_1_1Segment__Delaunay__graph__2.html#a140bb7cf97051f7de78de0e0778ff3ea

> Thanks a lot.
>
> Best,
>
> --
> Malcolm Mielle
> Ingénieur Robotique Polytech Paris UPMC
> mail : 
>
>  
> <mailto:>
> Tel : +33(0)782829386