CGAL users discussion list

[Monique Teillaud <>]

Hi

In 2D the result may depend on the order in which your algorithm is 
adding new points, in case of co-circular points.

But in any case CGAL triangulations stay deterministic and reproducible.
If you insert the same points in the same order, all runs will give you 
the same Delaunay triangulation.

best
        Monique Teillaud

Andreas Fabri wrote:
> 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