dolfin team mailing list archive

[Benjamin Kehlet <benjamik@xxxxxxxxx>]

2012/11/15 Johan Hake <hake.dev@xxxxxxxxx>

> On 11/14/2012 09:51 AM, Benjamin Kehlet wrote:
> > 2012/11/14 Anders Logg <logg@xxxxxxxxx <mailto:logg@xxxxxxxxx>>
> >
> >     Dear all,
> >
> >     The plot and csg branches have been merged into trunk. Please try out
> >     the new functionality for mesh generation (from both CSG descriptions
> >     and input files) and plotting and report any problems.
> >
> >     All thanks to very good work from Benjamin, Joachim and Johannes.
> >
> >
> > It is a little bit early to applaud. There are some issues with the csg
> > stuff that need to be fixed, so mesh generation (in particular in 3D) is
> > likely to crash.  I've have pushed everything to trunk, though, since
> > some of the plotting code depends on parts of the csg code.
>
> It crashes, but almost randomly. The same script (3D demo) sometime
> generate a nice mesh, other times a crappy one, and sometimes just crash.
>
> > Will report back when this has been fixed.
>
> What is the main cause for this erratic behavior?
>

It might be related to the cgal version but I think the main problem is
that the cgal mesh generator assumes as input a triangulated surface with
no degerated triangles and no self intersections.

The csg operations is carried out with exact number types and the resulting
polyhedron is then converted to floating point numbers. This conversion
introduces round off errors that often leads to self intersections. I'm
working on removing the self intersections now. Hopefully this will solve
the problem.

The reason that is only fails sometimes, is that cgal uses a random numbers
to get some initial points on the surface. It is possible to feed these
points to cgal and it would be a good thing, but I haven't look into that
yet.

Benjamin


>
> Johan
>
> > Benjamin
> >
> >
> >     --
> >     Anders
> >
> >     _______________________________________________
> >     Mailing list: https://launchpad.net/~dolfin
> >     Post to     : dolfin@xxxxxxxxxxxxxxxxxxx
> >     <mailto:dolfin@xxxxxxxxxxxxxxxxxxx>
> >     Unsubscribe : https://launchpad.net/~dolfin
> >     More help   : https://help.launchpad.net/ListHelp
> >
> >
> >
> >
> > _______________________________________________
> > Mailing list: https://launchpad.net/~dolfin
> > Post to     : dolfin@xxxxxxxxxxxxxxxxxxx
> > Unsubscribe : https://launchpad.net/~dolfin
> > More help   : https://help.launchpad.net/ListHelp
> >
>
>