GetBounds() fails on VTK9 with NaN points

I originally posted this issue here: https://discourse.vtk.org/t/getbounds-fails-with-nan-points-in-vtk9/4351

Check out this surface mesh which has a scalar array that contains NaNs: surface.vtp

If I apply a warp by scalar filter, the resulting mesh will have NaN points. This is fine and expected and works wonderfully on VTK<9, but on VTK==9, it does not work.

I noticed this issue while trying to plot this warped mesh with PyVista and ParaView with VTK9 which does not work because the rendering routines rely on GetBounds returning the non-NaN bounds. i.e. ParaView cannot display a mesh that contains NaN points.

Here are some details with VTK-Python

import vtk

reader = vtk.vtkXMLPolyDataReader()
reader.SetFileName("surface.vtp")
reader.Update()
surface = reader.GetOutputDataObject(0)

alg = vtk.vtkWarpScalar()
alg.SetInputDataObject(surface)
# args: (idx, port, connection, field, name)
alg.SetInputArrayToProcess(0, 0, 0, 0, "my data")
alg.SetScaleFactor(1.0)
alg.Update()
output = alg.GetOutputDataObject(0)

print(output.GetBounds())

Output:

VTK 8.x	VTK 9.x
(639926.0, 728426.0, 5669105.0, 5818551.0, 218.24110412597656, 1170.1644287109375)	(nan, nan, nan, nan, nan, nan)

To add to the oddness, (in VTK9) GetBounds() on the vtkPolyData object returns Nan while GetBounds() on the vtkPoints returns the correct bounds

>>> output.GetBounds()
(nan, nan, nan, nan, nan, nan)
>>> output.GetPoints().GetBounds()
(639926.0, 728426.0, 5669105.0, 5818551.0, 218.24110412597656, 1170.1644287109375)

---

@lassoan, did the leg work of figuring out what is going on in that discourse issue. It seems like this would be low hanging fruit for a new VTK developer. See their fix here: https://github.com/lassoan/VTK/commit/92b1ee09385c271a88dc4d38d8ce4e4dc5940d9f