How to extract a subset of a StructuredGrid through thresholding?

[Aleksey Naumov]

Please excuse duplicate postings, if any...

Dear VTK users,

I am struggling with the question - how to extract a subset 
from a StructuredGrid dataset based on its scalar value?

Basically, I need to perform scalar thresholding (mentioned 
on p. 374 of the VTK book; unfortunately, it doesn't say there
how to do it). I have an image and I'd like to separate area of
interest from the background - this could be easily done through 
scalar thresholding, since the background has a unique value.

But how do I extract the area of interest? vtkExtractGeometry 
needs an implicit function (and my area is very irregular).
vtkClipPolyData allows to set threshold with SetValue(), but I 
don't need clipping, I prefer to extract whole cells.

Thanks,

Aleksey


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