[Insight-users] questions about affine registration

[Michael Schildt]

Hello Everybody!

I'm new to the toolkit and started using the ITK for registration of 
inter-modal, intra-subject 3D MRI datasets. I worked through the 
examples delivered with the software. I tried to make my own programm 
based on one example to make a centered affine 3D transform and perform 
registration using MattesMI, linear interpolation and 
RegularStepGradientDescent and results aren't satisfying . The tranform 
was initialized via TransformInitializer using the moments of both 
datasets. Maybe still some understanding problems remained for me:

1) What is optimizer->SetScale() really doing?
As far as I understood it helps me to make parameters of the transform 
beeing in the same number range for optimization. So setting it to 
values smaller
one for that parameter it will make smaller otimization steps? What 
happens if the value is zero. I thought will fix this parameter, but it 
didn't. :-/

2) What is the Method transform->SetFixedParameters() for? The 
documentation just says, it fixes the parameter. :-(

I want to fix some of the parameters for the registration, making a 
scaling as first step, followed by complete affine transform. Can I do 
this with with one of above mention methods?

Best regards,
    M. Schildt