BUG: VTKPolyDataMeshIO should not hang on inf and NaN in ASCII .vtk file

[N-Dekker]

MeshFileReader/VTKPolyDataMeshIO did hang forever when trying to read an
ASCII .vtk file that contained non-numeric chars in "POINTS" section, for
example "Infinity" or "NaN".

With this commit, "inf" and "Infinity" will be interpreted as the floating point
value infinity, while "nan" and "NaN" will be interpreted as Not-A-Number. Other
strings of non-numeric characters in the list of point components (coordinates)
will cause the reader to throw an appropriate itk::ExceptionObject.

Addresses issue #3539
"MeshFileReader/VTKPolyDataMeshIO hangs forever on non-numeric chars in "POINTS"
section (including "Infinity" and "NaN")"

[Leengit]

Is it worth it to go completely case insensitive to catch "Inf", "Nan", etc.?

[N-Dekker]

Is it worth it to go completely case insensitive to catch "Inf", "Nan", etc.?

@Leengit Good question! "Infinity" and "NaN" are essential because those are the strings produced by ITK's MeshFileWriter, using itk::VTKPolyDataMeshIO (which internally uses https://github.com/google/double-conversion). However, it appears that VTK prints infinity and Not-A-Number via printf-style "%g" formatting. Which yields "inf" and "nan" (both entirely lowercase).

I'm not aware of any other string representation of infinity and Not-A-Number that is actually being used in .vtk files.

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FYI, This is where our (ITK) "Infinity" and "NaN" strings come from: https://github.com/google/double-conversion/blob/af09fd65fcf24eee95dc62813ba9123414635428/double-conversion/double-to-string.cc#L44-L49 While here is where I see VTK using "%g" to output floating points: https://gitlab.kitware.com/vtk/vtk/-/blob/54a30648db36cab3b91d140a30b14176f97c254a/IO/Legacy/vtkDataWriter.cxx#L1299

Just double-checked: VTK's vtkPolyDataWriter does indeed write "inf" and "nan" for infinity and NaN values respectively, as I just tried, after building the latest version of VTK, from https://gitlab.kitware.com/vtk/vtk/-/tree/54a30648db36cab3b91d140a30b14176f97c254a/ using VS2019.

[thewtex]

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