[Insight-users] ResampleImageFIlter discards input image's spacing?

[Zachary Pincus]

Hello,

 From a brief look at the code, it appears that the 
itk::ResampleImageFilter class uses a default origin of all zeros and a 
default spacing of all ones, if SetOutputOrigin() and 
SetOutputSpacing() are not called.

This doesn't seem to be the most intuitive behavior -- is would seem 
more correct for the ResampleImageFilter to use the input image's 
origin, and *especially* its spacing than defaulting to something 
arbitrary. That is, given the importance of the spacing values in ITK 
and the fact that a resampler is probably more likely to be used in a 
geometric transform than to change spacing values, it seems like 
throwing away the input image's spacing information by default might 
not be the right way to go. Moreover, if I recall correctly, other 
image filter classes just pass along the origin and spacing of the 
input, so this seems even more at variance.

Is this in fact the case, or did I overlook the part of the code where 
the ResampleImageFilter actually does, by default, retain the input 
image's spacing?

Zach Pincus
Department of Biochemistry and Program in Biomedical Informatics
Stanford University School of Medicine