CGAL users discussion list

[Olivier Devillers <>]

Hanjoerg Seybold a écrit :
> Hi!
> Nobody has an idea how to obtain the direction of infinite halfedges?
> thanks hj
> Hanjoerg Seybold writes:
> > Hello!
> > I am making calculations with voronoi diagrams. For my application i 
> > have to intersect the unbounded edges/halfedges with a boundary given 
> > by a polygon or a segment or line. After studying the manual and i am 
> > a bit confused about the halfedge structure. 
> > 1. it is said that "Halfedges are oriented edges", but i cannot find a
> >   method how to access  the orientation. 
from source to target !

> > 2. It is possibe to check if a halfedge IS a segment or ray. h.is_ray(),
> >   but if the halfedge IS a ray, how can i access its features 
> > (direction,
> >   etc.)?
I agree that such a function should be there.

Anyway you can get dual()->segment() to get the dual Delaunay edge
and rotate it by 90 d. to get the direction

> > 3. My Problem is that i iterate through the halfedges and i want to 
> > know if
> >  a infinite halfedge intersects a polygon. For this i wanted to 
> > construct
> >   a  line ray etc out of the halfedge, but i dont know how to obtain the
> >   direction in the case that the halfedge has only source OR target. 
> > Any help would be welcome 
> >   hansjoerg
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