CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Laure Guicherd wrote:
> Hi all,
> I'm kind of stuck with this issue with Voronoi 2D. I know this topic has 
> been discussed a lot in this mailing, but I could not find a solution in 
> the archives.
>
> I am getting a Voronoi diagram from successive sites insertions, then i 
> want to get its faces and vertices. Since i want to bound this diagram 
> with a convex hull, i need to get the intersection of the diagram edges 
> with this hull, and in this purpose i want to convert each halfedge to 
> Segment_2 or Ray_2 in order to test this intersection.
>
> Here is my (simplified) code :
>
>
>
> typedef typename CGAL::Delaunay_triangulation_2<K> DT;   typedef 
> typename CGAL::Delaunay_triangulation_adaptation_traits_2<DT> AT;
> typedef typename 
> CGAL::Delaunay_triangulation_caching_degeneracy_removal_policy_2<DT> AP;
> typedef typename CGAL::Voronoi_diagram_2<DT,AT,AP> Voronoi;
> typedef typename Voronoi::Face_iterator Face_iterator;
> typedef typename Voronoi::Ccb_halfedge_circulator Ccb_halfedge_circulator;
> typedef typename AT::Site_2 Site_2;
>
>
> Voronoi VD;
>
> // for each point [x,y] :
> VD.insert( Site_2(x,y) );
>
> for ( Face_iterator bf = VD.faces_begin() ; bf != VD.faces_end() ; ++bf )
> {
>    Ccb_halfedge_circulator firstEdge = (*bf).outer_ccb();
>    Ccb_halfedge_circulator he = firstEdge;
>    do
>    {
>        CGAL::Object obj = make_object(he);
>
>        Segment_2 segment;
>        Ray_2 ray;
>        bool isSegment = ( CGAL::assign( segment, obj ) );
>        bool isRay = ( CGAL::assign( ray, obj ) );
>
>        // test intersection, get points, etc.
>    }
>    while ( ++he != firstEdge );
> }
>
>
> My problem is that isRay and isSegment always return false, even when 
> he->is_ray() or he->is_segment() are true.
>
> What did i do wrong ? How can i make this conversion ?
> Any hint will be greatly appreciated, thank you !
>
> Laure

This post could help you.

https://lists-sop.inria.fr/sympa/arc/cgal-discuss/2007-06/msg00229.html


If you really need to use the approach with the adaptator, you can
find if a halfedge is on a ray or a segment using functions 
has_source() and has_target() like in this example:
http://www.cgal.org/Manual/last/doc_html/cgal_manual/Voronoi_diagram_2/Chapter_main.html#Section_44.5

Note that in the approach you are using, Voronoi diagram is described 
using a halfedge data struture. If you are not familiar with it, have a 
look here:

http://www.cgal.org/Manual/last/doc_html/cgal_manual/HalfedgeDS/Chapter_main.html

S.