Crinkle Clip returns UnstructuredGrid instead of PolyData about pyvista

[user27182]

remove_cells may be a good alternative to extract_cells. It has a PolyData to PolyData mapping. Though, the indices provided to these filters are kind of the inverse of each other. An alternative is to use vtkRemovePolyData for this purpose, this is what the connectivity filter currently uses under the hood for some cases.

Or, even using extract_surface would work, as suggested in #3009.

Not sure which implementation would be better to use. Some methods may alter the topology so probably whichever one best preserves the input data (e.g. correct cell winding, preserves orientation of the normals, ordering of cell ids, etc.

Having a PolyData to PolyData mapping for filters more generally is probably a good thing to add. It would eliminate the need to always cast the output back to PolyData if this kind of behavior was made standard for all DataSetFilters.
For example it would resolve this issue #5613.

Other filters such as extract_values, which also uses extract_cells under the hood and returns an UnstructuredGrid, would also benefit. E.g. #5968 uses extract_values but then has to call remove_cells to effectively cast the output back to PolyData. It would be nice to just get the PolyData output directly.

[darikg]

it's always irked me that PolyData.extract_cells returns an UnstructuredGrid. Big +1 on fixing that if it's possible

[user27182]

#6060 was recently patched into version 0.43.8, not sure if that affected the output. @kalingibbons do you get this same bug with 0.43.7 ?

[kalingibbons]

I was actually on 0.43.3 when I first ran into it, then updated to see if it was fixed before submitting the issue.

[user27182]

Ah ok thanks for checking, I guess this bug has been there for a while then.

[MatthewFlamm]

when doing crinkle clip, it uses extract_cells under the hood. This is the reason that it returns UnstructuredGrid. I wonder if If should detect PolyData input and then cast appropriately.

https://docs.pyvista.org/version/stable/api/core/_autosummary/pyvista.DataSetFilters.extract_cells.html#pyvista.DataSetFilters.extract_cells