CGAL users discussion list

[Michael Hoffmann <>]

> Since you can't(or I don't know how) convert unbounded half-edge into
> Ray_2, the reasonable solution would be calculate the direction by
> yourself using the sites position. But this also turn out to be
> difficult to do.


I suppose it would be nice to have a direct way of getting the ray as  
part of the interface, just as for finite edges/segments. Anyway:

For a Voronoi halfedge you can get the two defining Delaunay vertices  
in various ways, for instance, by down() and up() or via face()->dual 
() and opposite()->face()->dual(). Then define a vector between the  
corresponding points (the one on your side/face first) and obtain the  
direction of the ray via perpendicular(CGAL::CLOCKWISE).

Another option is to use dt.dual(halfedge->dual()), where dt is the  
underlying Delaunay triangulation. This returns a CGAL::Object, which  
can be cast into a ray (if it is a ray) using object_cast (as for  
intersections...).

If there's a more elegant way to do this, I'd be glad to hear...

hth,
Michael