[MINC-users] mincresample and linear 'deformations'

[Vladimir S. FONOV]

It looks like it's a problem of finding an inverse of the transformation 
outside of the domain where it's defined.

When you apply the transform do you apply it directly or with 
-invert_transformation ?


On 2016-08-17 11:54 AM, Alex Zijdenbos wrote:
> 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
>
> ​
>  lsq3_verify.png
> <https://drive.google.com/file/d/0B5fOtqpIs4sKd0U0UVQ3al95WTA/view?usp=drive_web>
> ​
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>


-- 
Best regards,

  Vladimir S. FONOV ~ vladimir.fonov <at> gmail.com