[Insight-users] problem with deforamtion field from DeformableRegistration15.cxx

[pinpress]

Hi,

I was able to compile the example program DeformableRegistration15.cxx (I
did not modify the example cxx source code), which performs rigid, affine,
and BSpline registration sequentially. The program also gives output image
as expected. However, in my application I need to get the deformation field.
I was able to read in the deformation field VTK file into Matlab, however, I
have trouble interpreting what it is exactly. For example, if my input
images are both of 3D matrix, 10-by-10-by-10. The deformation field I got
would be:

10-by-10-by-10-by-3

Which clearly tells that each voxel, there is a 3D displacement vector.
However, the displacement vectors just does not make sense. I was able to
verify that this displacement field is exactly a "rigid" deformation -- it
does not have any nonrigid component, but clearly the images were nonrigidly
deformed. So, what I am doing wrong here? 

By the way, I used the same analysis to the deformation field generated from
DeformableRegistration5.cxx (which is just a LevelSet registration, without
rigid or affine registration pre-processing), the displacement vectors do
make sense -- I can clearly see nonrigid deformation.

Thanks very much in advance for help.
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