[Insight-users] [ITK Community] Jacobian of an affine transform

[Luis Ibanez]

Hi François


On Wed, Jan 22, 2014 at 3:31 AM, francois rousseau <rousseau at unistra.fr>wrote:

> Hi there,
>
> I’m trying to check itkDisplacementFieldJacobianDeterminantFilter for
> affine transform and I get weird results.
>
> Basically, I’ve created a simple affine transform with a scale factor in x
> dimension :
>
> #Insight Transform File V1.0
> #Transform 0
> Transform: MatrixOffsetTransformBase_double_3_3
> Parameters: 1.5 0 0 0 1 0 0 0 1 0 0 0
> FixedParameters: 22.6774 -12.4914 6.04305
>
> I’ve converted this affine file to a deformation field using
> ComposeMultiTransform (from ANTS). The field is correct so far.
>
> Then, I computed the jacobian of the field
> using itkDisplacementFieldJacobianDeterminantFilter.
> Jacobian is constant and equal to 1.
>
> I would have expected 1.5 or 2/3.
>
> Am I doing something wrong?
>
>
>

Your intuition seems to be correct here.
It seems reasonable to expected the Jacobian to different from 1.0

Would you mind sharing your code ?

In that way we could give it a quick try at debugging,
and getting a better sense of what is happening.

   Thanks

          Luis
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