[Insight-users] Translation-then-Rotation transform?

[Zachary Pincus]

Hello, (and sorry to be so constantly emailing the list lately!)

I'd like to use a spatial transform that translates a point to a new 
space and then performs a rotation in that new space about the origin. 
Basically, I've got a moving image that I want to translate around a 
fixed image with the optimization framework, and rotate about its 
center. I'm not using the registration framework here; in reality I'm 
querying trying to find an optimal parameter fit of a PCA shape model 
to an image. So the "moving image" is really a PCA shape model.

Using the CenteredRigid2DTransform is a bit painful because it allows 
the optimizer to change the translation and center of rotation 
independently, whereas I have prior knowledge that the center of 
rotation should *always* be about the origin in the new space.

Now, I could make a different version of the Rigid2DTransforma and 
Euler2DTransform classes that would have this behavior (currently, they 
rotate-then-translate). Is there an easier method, though? Or would I 
really be better off for some reason using the 
CenteredRigid2DTransform?

(I've read the chapter about centered transforms in the software guide, 
but I don't see why optimizing over a 5-dimensional parameter space is 
any better for me in this case than over the more natural 3-dimensional 
<translate_x, translate_y, rotate> space.)

Thanks,

Zach