[Insight-users] registration without using moments or geometry

[Kajetan Berlinger]

Rick Shilling wrote:
> In doing itk registration, I already have a good initial estimate of the transformation WITHOUT using the itk::CenteredTransformInitializer momentsOn() or Geometry() methods.  With matrix & offset as my initial transform estimate I have:
> 
> ...
> transform->SetMatrix(matrix);
> transform->SetOffset(offset);
> registration->SetInitialTransformParameters( transform->GetParameters() );
> ...
> 
> Though on first iteration of registration->StartRegistration(); all points map outside the volume.  
> 
> As a sanity check, I then used itk::CenteredTransformInitializer with the momentsOn() method & was able to successfully register the volumes.  I then used that exact same initial estimate that MomentsOn() produced & hardcoded that matrix & offset as my initial transform REMOVING the itk::CenteredTransformInitializer object from the code.  Though, again, on first iteration of registration->StartRegistration(); all points map outside the volume.   Since it is clear that this initial estimate can provide working registration, do I need the itk::CenteredTransformInitializer object?  If not, what object/methods need to be called so that I can use my own estimate without having exceptions thrown?  
> 
> Thanks.
> Rick Shilling
>  
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Hi Rick,

you should use   transform->SetCenter( rotationCenter );
		 transform->SetTranslation( translationVector );
to initialize the registration, instead of using an initial transformation.
Then you will get the same result, compared to that of MomentsOn().

Just have a look at the code in itkCenteredTransformInitializer.txx (Method InitializeTransform()).

cu
kaj