[Insight-users] How to select the Optimizer used with ScaleVersor3DTransform

[Chunfang Wang]

Hello All,

I read the extensive explanation about how to select suitable optimizer for
different parameter space of the Transform.
http://www.itk.org/pipermail/insight-users/2006-September/019324.html

It is pointed about that the scale parameter in the Similarity Transform
*does not* form a vector space.
Scales shouldn't be added and subtracted. Their operation should be done in
a logarithmic space.

The Similarity Transform derived from VersorTransform :
ScaleVersor3DTransform is the object transform used in my experiment.
In my situation, I customize the three scale factors in ScaleVersorTransform
to be ( x_scale = y_scale = s,  z_scale = 1.0 ).
Thus, s is the only parameter in scale space I need to optimize.

For the optimization of this customized transform, I can follow the
Versor3DRigidTransformOptimizer to do with the rotation + translation
parameters.
But for the scale factor, I don't know how to add it into the
Versor3DRigidTransformOptimizer.
I am thinking whether I can just use the log of s to be the input variable
for the optimizer.

Hope someone can give me some help.

Thanks a lot.

Best,
Chunfang
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