[MINC-users] mincresample and linear 'deformations'

[Alex Zijdenbos]

Hi all,

I was always under the impression that one could turn a linear xfm into a
deformation field (using xfm2def), and that the application of the
resulting deformation would be equivalent to using the linear xfm. However,
mincresample disagrees.

In the attached image, I've created a simpe lsq3 (param2xfm -translation 10
20 30) linear xfm, generated a 'deformation' field out of that using
xfm2def (same lattice as the input volume), and resampled the input volume
with both xfms. Clearly, in the case of a 'deformation' xfm, the volume is
filled with unmodified voxels where I didn't expect them.

This is tied to the sampling lattice of the deformation field, which in
this example is the same as the input volume. The resamplings are done
using -use_input_sampling btw. The two bottom rows show the resampling
using a padded input volume (no change), and using a 'deformation' grid
with a larger extent (generated on a lattice that is 10 voxels larger all
around).

To pre-empt Vladimir, itk_resample behaves the same way ;-)

Bug, or feature? I'd say the former.

Thoughts?

-- A

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 lsq3_verify.png
<https://drive.google.com/file/d/0B5fOtqpIs4sKd0U0UVQ3al95WTA/view?usp=drive_web>
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