CGAL users discussion list

[Pratyush Pranav <>]

On 14 Apr 2016, at 13:19, Monique Teillaud <> wrote:

On 14 Apr 2016, at 10:10, Pratyush Pranav <> wrote:

 by the way, is it true that a simplex that belongs to convex hull may actually not be a part of the triangulation?

not sure what you mean. Of course if you have coplanar points on the CH, then the triangulation of a facet with >3 vertices is not unique. The facet can be triangulated in some way by some algorithm, and in a different way by another. 

i do not think i am encountering this case…my points points for triangulation are on s2, so no coplanar points really, but great circles parallel to the equator, with equal spacing.

also, more importantly, when i output the infinite vertex it gives me the coordinates as (0,0,0).

I guess it depends on the compiler. In any case you are not supposed to access the coordinates of the point in it, they don’t mean anything, and the algorithms never use them. 

yes, was just curious, of course i am not using them

i faintly remember reading in the coal manuals that for points on sphere, there is an insertion of a dummy point at (0,0,0)…

How can the algorithm know in advance that all points will be co-spherical? I imagine that you are making a confusion with the following: when you know in advance that your points are co-spherical, a common advice is to insert an additional point inside the ball that they form, in order to avoid having only degeneracies in your set of points. 

so now, i convert to convex hull, and write it to a polyhedron_3. by the way, i think i have my answer. the halfedges are unique to a facet from what it looks like on the polyhedron documentation.

indeed, reading the manual is often useful ;)

still pretty much not getting what i want to, but treading through it…more on this in a separate mail that follows..

pratyush