CGAL users discussion list

[Ramin H <>]

Thank you for your comments.

I was not accurate in my previous email. The bad tetrahedra I was talking about were actually having small dihedral angles and other criteria were met. Apparently, it is possible for a tehrahedron to be close to flat and have a radius-edge <= 3. That's interesting.

I applied Lloyd, perturber and exuder and now the number of tetrahedra with small dihedral angle has dropped considerably. 

Are there any plans to introduce NODT into CGAL? It looks like it is more effective in removing slivers. ("Interleaving 
Delaunay Refinement and Optimization
for Practical Isotropic Tetrahedron Mesh Generation" http://www.geometry.caltech.edu/pubs/TWAD09.pdf). 

Thank you,
-Ramin

On Fri, Jul 9, 2010 at 4:05 AM, Mariette Yvinec <> wrote:

Hi Ramin

if your Finite Element Analysis really needs a good quality mesh,
you should also activite others optimisation process.
The best combination is to launch a few Lloyd iterations,
then the perturber, then the exuder

Stephane Tayeb wrote:

Ramin H wrote:

Hi everyone,

I am using the Meshe_3 in CGAL 3.6. The meshing criteria is as follows:
Cell Aspect Ratio: 3.0
Facet Angle: 25

And I have turned on Exuding. When I inspect the mesh, I can still see
plenty of tetrahedra that are violating the aspect ratio rule. I am using
the resulting mesh for a Finite Element Analysis and the quality of mesh has
a significant impact on the accuracy of the results.

How can I get rid of all (or most) of bad tetrahedra?

Thanks,
-Ramin

Hi Ramin,

After the mesh generation step, you should have a mesh that fulfills your criteria, i.e. every tetrahedron of the mesh should have a *radius-edge ratio <= 3* (is that what you call aspect ratio ?)

As the sliver exudation process tries to increase the smallest dihedral angle in the mesh, there is no guarantee that the radius-edge ratio would not decrease during exudation.

What are your criteria to consider a tetrahedron is bad ?

Best,
Stéphane.

--

Mariette Yvinec
Geometrica project team
INRIA  Sophia-Antipolis  

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