[Paraview] [EXTERNAL] python calculator confusion

[David Thompson]

Hi all,

> ...
> 1. Make sure you set "Array Association" on "Python Calculator" to "Cell Data".
> 2. The volume() code internally uses vtkCellQuality filter. Now, when
> I debugged into it, I see that is doesn;t support voxel cell types --
> the cells produced by vtkImageData.

Yes, that is an artifact of using the verdict library to compute volume. The cell quality filter is being used to compute a "quality" metric that is rarely used as a primary indicator of mesh quality, so this is not really the intended use of the filter. The cell quality of axis aligned boxes is not usually of interest to anyone, so when writing the quality filter I did not consider that cell type... only those types directly supported by verdict. While volume can be obtained for other types by tetrahedralizing and summing, that does not work for other metrics like Frobenius norm. Many element shapes do not have well-characterized quality metrics.

    David