[Insight-users] Multi Resolution Registration

[Luis Ibanez]

Hi Robert,

There is no generic way of converting an AffineTransform into
a rotation. If there is any shearing or anisotropic scaling
in the matrix, the notion of rotation can no longer be isolated
from the matrix.

If you want to recover a rotation, you should use the RigidTransform.

In particular you may find useful the QuaternionRigidTransform
if you are working with 3D images.
http://www . itk . org/Insight/Doxygen/html/classitk_1_1QuaternionRigidTransform . html

This transforms is described in the SoftwareGuide
http://www . itk . org/ItkSoftwareGuide . pdf
in Section 8.7.9, pdf-page 301, paper-page 327.
 From this transform you can recover the rotation in
the form of a unit quaternion (aka Versor).


Yes, you can use other metrics and other transforms,
that's the advantage of the modular design of the
registration framework in ITK.

This particular example was doing multi-modality registration,
in which case your options are limited to the four different
implementations of MutualInformation available in the toolkit

Viola-Wells
http://www . itk . org/Insight/Doxygen/html/classitk_1_1MutualInformationImageToImageMetric . html
Mattes
http://www . itk . org/Insight/Doxygen/html/classitk_1_1MattesMutualInformationImageToImageMetric . html
Histogram based
http://www . itk . org/Insight/Doxygen/html/classitk_1_1MutualInformationHistogramImageToImageMetric . html
Histogram based normalized MI
http://www . itk . org/Insight/Doxygen/html/classitk_1_1NormalizedMutualInformationHistogramImageToImageMetric . html


In transforms you have all the options described in the
SoftwareGuide in section 8.7, pdf-page 294, paper-page 320.

A generic lit of transform is also available with
the Doxygen documentation
http://www . itk . org/Insight/Doxygen/html/group__Transforms . html

It is up to you to select the transform that is appropriate for
modeling the missalignment of your images.


Please let us know if you have further questions.


Thanks


   Luis


-------------------------------
Robert-Paul Buitendijk wrote:
> Hello everyone
> 
> The 2nd example in the softwareguide provides a matrix which describes the
> rotation,scaling and shear of the picture.
> In the guide there is no mention of how to convert the matrix back to a
> rotation. How can i do this???
> Is it also possible to use other metrics and transforms, or isn't that an
> advantage?
> 
> Tnx Robert
> 
> 
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