CGAL users discussion list

[Laure Guicherd <>]

Hi Khuong,

You are absolutely right. I have a diagram like this one : 
http://www.olivierlanglois.net/images/voro2.jpg
which i want to bound with a Rectangle (say, the borders of the image)

I hear your solution, but the problem remains, that even if the source 
or target does not exist (infinite edge), I need the direction of the 
edge to calculate its intersection with a the rectangle. This is why i 
want to convert this edge to Ray_2.

Moreover, if an edge is finite (i.e. if it has a source AND a target), 
sometimes it will intersect this rectange as well. That is why I need to 
convert it to Segment_2.

In the second case, I could create this segment from the source and 
target point and test the intersection, but in the first case (infinite 
edge), I cannot figure how to get this intersection if only have one 
point and no direction, and cannot convert the edge to Ray_2.

I hope i have made myself clear :) Thank you for your help Khuong.

Vu, Khuong wrote:
> Hi Laure,
>
> Let me see if I understand your problem correctly. You have a set of segments 
> (sites), which possibly intersect with each other. You then construct the 
> Voronoi diagram, and test if the face of each (possible divided due to 
> intersections) site is close of open.
>
> If so, you can use the function has_target or has_source to check if a 
> segment if infinite. Hope this helps.
>
> Best,
>
> Khuong
> ________________________________________
> From: Laure Guicherd 
> []
> Sent: Monday, April 12, 2010 10:05 AM
> To: 
>
> Subject: [cgal-discuss] Voronoi 2D : convert Halfedge to Segment_2 or Ray_2
>
> 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
>
> --
> You are currently subscribed to cgal-discuss.
> To unsubscribe or access the archives, go to
> https://lists-sop.inria.fr/wws/info/cgal-discuss
>
>
>