CGAL produces degenerate cells

[Jan Blechta]

from dolfin import *

mesh = Mesh(Circle(0.0, 0.0, 1.0) - Circle(0.0, 0.0, 0.3), 10) 

print 'Minimal radius ratio of mesh:', MeshQuality.radius_ratio_min_max(mesh)[0]
exec(MeshQuality.radius_ratio_matplotlib_histogram(mesh, 200))

for c in cells(mesh):
    if c.radius_ratio() < 1e-5:
        print 'Degenarate cell', c.index(), ', radius ratio', c.radius_ratio()
        for v in vertices(c):
            print '  ', v.point().str()

[Prof Garth Wells]

More specifically, I think you'll find that the CSG code, which turns circles in polygons, is the problem. CGAL meshes generated via implicit surfaces are usually good.

[Jan Blechta]

Is the code you mention part of DOLFIN or CGAL? If the former is true, this issue can be modified when someone digs into the problem.

[Benjamin Dam Kehlet]

I'll take a look at this. Garth: I don't think CGAL can mesh implicit surfaces in 2D. The mesh generator in 2D and 3D are very different.

[Prof Garth Wells]

@benjamik yes, you're right. I thought I programmed implicit surfaces for 2D, but I did in fact turn circles into polygons too!

[Prof Garth Wells]

Fix merged in 80b0906.