[vtkusers] vtkMeshQuality broken?

[Dominik Szczerba]

Oh yes, after flipping my tets I seem to be geting the old numbers. I don't 
believe these should depend on tet orientation though. I once raised this 
issue with MathWorld (and was finally agreed with). Orientation is not always 
(needed to be) maintained and quality as radius ratios by definition is 
always positive. If one wants one can make an extra separate check, 
otherwise, there might be an unnecessary frustration.

Thanks a lot for your valuable answer!
Dominik

PS. I could not find a vtk class to flip tets, small issue though.



On Friday 30 March 2007 03:12, you wrote:
> > The values in quality.GetOutput().GetCellData().GetScalars("Quality") are
> > not OK, 1e30 in my case. Setting VolumeOn() and RatioOn() seem to do give
> > some numbers, but they seem more (signed) volume than quality. I am
> > pretty sure I have made no changes to this code for months.
>
> I ran the filter on tetraMesh.vtk in VTKData and noticed that the 1e30
> is returned for each and every cell with negative volume (and no
> others). This is probably a result of switching to use the quality
> metrics computed by the Verdict library as Philippe Pébay announced a
> month of so ago. Since this behavior (returning an invalid value for
> inverted tets) doesn't match the documentation for the Verdict library,
> I will take up how best to fix it with the Verdict folks. I would not be
> surprised if they wish to keep the current behavior and adjust the
> documentation since negative volumes often indicate serious trouble with
> the algorithm that produced them. In that case, you should orient
> tetrahedra properly before sending them to vtkMeshQuality. I believe
> there's a filter that will reorient tets but I don't remember the name
> of it offhand.
>
> Thanks for the heads up on the python test; it needs to be updated. I
> don't think it could have worked for over 2 years given that it assumes
> the output mesh's field data has scalars set. (We do produce field data
> arrays, but there are 4 of them -- one for each element type supported
> -- each of which has a 5-tuple holding descriptive statistics, instead
> of a copy of the per-cell results.)
>
> 	David
>
> > Thanks for any hints,
> > Dominik
> >
> > On Friday 30 March 2007 00:08, David C Thompson wrote:
> > > > vtkMeshQuality does not work for me any longer (both C++ and python).
> > > > I do as simple as: vtkUnstructuredGridReader -> vtkMeshQuality ->
> > > > vtkUnstructuredGridWriter with setting Input/Output connections as
> > > > usual. It always worked now not anymore. In the docs I read about
> > > > some compatibility issues (VolumeOn, RatioOn()) - were there recent
> > > > changes? The test referred to there (meshQuality.py) does not work.
> > >
> > > Can your provide more information about what doesn't work? Does the
> > > filter not compile, not run, yield no results, or incorrect results?
> > >
> > > 	Thanks,
> > > 	David

-- 
Dominik Szczerba, PhD
Computer Vision Lab CH-8092 Zurich
http://www.vision.ee.ethz.ch/~domi