[Insight-users] Inverse of ScaleSkewVersor3DTransform

[Karthik Krishnan]

Please correct me if I am wrong:

A ScaleSkewVersor3DTransform is exactly the same as an AffineTransform, 
with a more intuitive representation of parameters. (ie the 3 scales and 
6 skews in addition to the versor and translation)

The inverse is then the inverse of the affine matrix, which is another 
affine transform.

I am pretty sure somebody has done the math to decompose an affine 
transform into the scale, skew, Rotation matrix and translation 
components. At least it sounds like something one would often want to do 
to get a meaningful interpretation from an affine transform. If you do 
find that, we could add it back into the class.

Regards
karthik

Ranjan, Sohan (Research) wrote:

>I am doing registration using the ScaleSkewVersor3DTransform. As per ITK
>registration convention, the transform returned is from the fixed image space 
>to the moving image space. I am not using the resample filter for resampling
>the moving image due to certain reasons, so I need to find an inverse of the
>transform myself. But it looks like that the inverse for ScaleSkewVersor3DTransform
>is not defined.
>
>Can someone suggest how should I go about constructing the inverse?
>
>Sohan 
>
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