[vtkusers] lookuptable scalar range rounding

[Sebastien_MARAUX]

Hello again, again...

When vtkLookupTable maps scalars to its entries,
it usually takes the floor() value after aplying a simple 
ratio.

Is it possible to tell vtkLookupTable to choose nearest
value instead ??

I would like to use a even number of entries, and doing so it 
is not possible to keep the negative to positive change clear.
(ie. mapping a -x to x scalars to a 256 entries colormap will
lead to a mapping of positive values to the colorid 127, 
which is less than half of the colormap, but I want colorids 
<=127 for oceans (x<0) and colorids >127 for floor (x>0) )

I am currently using a 255 or 257 entries lookuptable.
(then id 127 or 128 is exactly mapped to x=0)

Seb
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