[Insight-users] Combining transforms in registration?

[Luis Ibanez]

Hi Jaety,

You have the option of using an even better solution.

Since you know the rotation parameters, you can simply use them
for initializing the rotational component of the Rigid transform.

You don't need to create any new Transform for doing this,
just use the itkVersorRigid3DTransform, and use the rotation
parameters in the Versor. Note that if what you have are Euler
angles, you should convert them to a Versor by passing first
through a rotaion matrix.

What you should carefully choose is the "Center of Rotation"
this parameter is of great importance, since it relates closely
to the Translation that you will obtain at the end.

For details on this relationships, please read the ITK Software Guide:


          htt://www.itk.org/ItkSoftwareGuide.pdf


in particular the Section on "Transforms" in the "Image Registration"
Chapter.


By playing with the parameters scaling values, you can arrange
for the optimizer to focus on changing the translation parameters
of the Rigid transform and leaving almost unchanged the rotational
parameters.



    Regards,


        Luis


--------------------
Jaety Edwards wrote:
> Hello all,
> 
> I'm trying to figure out the best way to solve the following problem:
> 
> I have two 3D images that I am trying to register. I know that they
> differ by a rigid 3D transformation, and also I know the 3 rotation
> parameters, so all I have to solve for are the translation parameters.
> 
> What I'm doing right now is resampling the image into the correct
> orientation and then using a TranslationTransform in the registration
> process, but it seems like it would be cleaner if I could just pass
> both original images to the registration and use a transform that
> applies my known rotation and then acts like the standard
> TranslationTransform.
> 
> I figure it shouldn't be too difficult to inherit or build off of the
> existing TranslationTransform to do this, and I was going to look into
> that next, but I'm a pretty new ITK user, and I thought I would ask
> here if there was an easier way to do this before diving in.
> 
> Thanks so much,
> Jaety
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