Comment 2 for bug 1082157

On Fri, Nov 23, 2012 at 10:19:03AM -0000, Joachim Haga wrote:
> On reflection, perhaps it is correct after all. The diameter in
> question is the diameter of the sphere with all four vertices on the
> surface; i.e., it goes to infinite as the cell degenerates.

Is the problem a tet in a corner of the mesh? Explains why I couldn't
fix it by a simple smoothing.

> What the glyph scaling requires is really a measure of the
> characteristic cell size; something with a reasonable maximum value
> even in the presence of some bad cells in the mesh. It could be
> incircle/insphere, or just longest side length. Is there a method to
> calculate this for a (general) cell?

No, but we could easily add something to the Cell class to compute
that, perhaps Cell::longest_edge_length(), or max_edge_length()? We
could also add min_edge_length().

--
Anders

> On 23 November 2012 08:08, Anders Logg <email address hidden> wrote:
> > ** Changed in: dolfin
> > Assignee: (unassigned) => Anders Logg (logg)
> >
> > ** Changed in: dolfin
> > Importance: Undecided => Medium
> >
> > ** Changed in: dolfin
> > Milestone: None => 1.1.0
> >
> >
> > Title:
> > Bad cell diameter in gear mesh
> >
> > Status in DOLFIN:
> > New
> >
> > Bug description:
> > See https://bugs.launchpad.net/bugs/1034187.
> >
> > The mesh used in the elasticity demo
> > (demo/undocumented/elasticity/python/gear.xml.gz) reports a very large
> > hmax(). hmax() is reported as 36.001, but the whole mesh is smaller
> > than 1 in all directions. Maybe related to numerical precision for
> > nearly degenerate cells?
> >
> > from dolfin import *
> > mesh = Mesh("gear.xml.gz")
> >
> > c = Cell(mesh, 18847)
> > print c.diameter()
> > # 36.001483031
> >
> > print c.volume()
> > # 7.373890632542822e-11
> >
> > To manage notifications about this bug go to:
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>