[ITK] [ITK-users] Smallest region containing the physical space covered by another image's region

[Cyril Mory]

Hi ITK users,

I am preparing a patch for the itkWarpImageFilter, and I came to realize 
that computing the requestedRegion of the inputs from the output's 
requested region is non trivial.

- the displacement in the deformation field can be very large, in any 
direction, ... therefore there is no choice but to load the full input 
image into memory (unless we want to go through the whole deformation 
field to evaluate the maximum displacement, but in a method like 
GenerateInputRequestedRegion we do not want such heavy processing)
=> Input image's requested region should be the largest possible region

- the requested region in the deformation field, on the other hand, can 
be computed. But it is not trivial. If the output and the DF have 
identical information (spacing, origin, direction), then the requested 
region in the DF should be copied from the output. If their information 
differs, computing the requested region would require a method to 
compute the smallest rectangular region that contains the physical space 
covered by an other image's region, the other image having (potentially) 
a different spacing, origin and/or direction. Does such a method exist 
somewhere in ITK ?

Cyril
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