[Insight-users] itkFixedCenterOfRotationAffineTransform

[Simon Warfield]

Marius Staring wrote:

> Hi,
>
> we noticed that the FixedCenterOfRotationAffineTransform has dimension 
> * (dimension + 2), which equals 15 in 3D, but it should be 12, so 
> dimension * (dimension + 1). Nothing is done with the last 3 
> parameters, as it should be because 
> FixedCenterOfRotationAffineTransform has a FixedCenterOfRotation.
>
> Are these thoughts correct and is this a bug, or am i missing something?
>
> Regards,
>
I noticed some other inconsistencies in the transform parameterizations.
The registration examples illustrate the need to using scaling in the 
optimization, especially to balance translation against other parameters.
The AffineTransform and QuaternionRigidBody transform have translation 
parameters as the last of the parameters.
The Similarity3DTransform has:
http://www.itk.org/Doxygen/html/classitk_1_1Similarity3DTransform.html#z1527_1
``There are 7 parameters. The first three represent the versor, the next 
three represent the translation and the last one represents the scaling 
factor.''

I don't see an easy way to plug different transforms into a generic 
class that sets the scales for the optimizer. It seems that special 
arrangements would need to be made for each different transform being 
used, to work out which parameter indexes correspond to translations, 
and to set them specially.

-- 
Simon