Compute mesh quality statistics

[Prof Garth Wells]

Add support for computing mesh quality measures, with output for 2/3D visualisation and histograms.

This would be really helpful for identifying problems in complicated 3D meshes, and in assessing linear solver performance.

[Chris Richardson]

What about using Cell::radius_ratio() ?

[Prof Garth Wells]

Yes, that a good ingredient.

I want a function that I can just call on a mesh to get quality statistics.

[Johan Hake]

There are different quality measures for 2D and 3D cells. Maybe we should extend TriangleCell/TetrahedronCell with these measures and then add a utility function to output these as histograms (dolfin::Tables) or a CellFunction. On the fly I can come up with:

• Volume (area in 2D)
• Dihedral angle (only for tets)
• Aspect ratio (shortest over longest edge)
• Radius ratio

[Prof Garth Wells]

Basic tools committed.