CGAL users discussion list

[Andreas Fabri <>]

Hello,

If you develop an algorithm ON TOP OF CGAL, how can you expect us to tell you
if your algorithm is deterministic. We don't know your code.

CGAL Delaunay triangulations as such may give you different results
when you have co-circular points, for example points on a grid.
The diagonals can be oriented differently, and this even in every run.

andreas


panayiotis foteinos wrote:
> Hello all.
>
> I have implemented a Delaunay Refinement algorithm on CGAL. All the decisions 
> made in the algorithm are deterministic: multiple runs on the same input PSLG 
> should produce exactly the same mesh.
>
> I observed, however, that the output mesh is not the same after each run. 
> Fortunately, the ouput mesh is the "correct" one after each run (I am sure 
> about the correctness of the refined output mesh), but different. For 
> example, the meshing of the PSLG for the first time yields 1500 faces, while 
> the second time yields 1510.
>
> I am sorry I am asking you this but (after spending a lot of time debugging) I 
> have to be sure:
>         Is this behavior possible or there is a bug in my code? Should I 
> expect the             
> same answers from CGAL (with the same input) when no exact constructions are 
> used?
>
> The number type I am using is double, while the predicates are exact.
>
> Thanks,
> Panagiotis