[Paraview] NULL value support is unclear.

[Ajjp V W]

Dear Paraview Users,

Is there some guidance on the treatment  of  data  sets  which  contain some
missing, NULL or mask data areas? For instance, if some vtkImage or
vtkStructuredGrid, the data may contain some internal holes, or irregular
boundary, denoted by  special  values,  such  as  -9999. How can this
special value be denoted,  so it is avoided by filters? Is there support for
the NULL data  concept  within  the  VTK  data  structures?  If so, are
these exposed  within  ParaView  filters?  I can see that a filter such
as threshold  could  be applied to create an unstructured mesh ignoring NULL
 cells,  or  the  data  loader  itself could perform this task, however
 this  destroys  structured  data  coherence. There is a NAN color  menu  in
 the color editor. How does this work? Is there some example? Is NAN
detection implemented within all ParaView filters?

Any hints or suggestions are welcome!

Thanking you.

Sincerely,
ajjp.vw
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