[Insight-users] how to calculate displacement from B-Spline parameters

[pinpress]

Hi Marius,

The code is exactly the registration example program
DeformableRegistration15.cxx -- I only modified the # of iterations. I also
checked the code, and found the following lines:

  bsplineTransformCoarse->SetBulkTransform( affineTransform );
  bsplineTransformFine->SetBulkTransform( affineTransform );

Therefore, I think the bulk transformation was indeed set properly.?

Also, I am attaching two larger PNG files, hope it enhances visualization
(sorry for the negligence earlier). 

http://www.nabble.com/file/p20231967/output_Affine_BS.png
output_Affine_BS.png 
http://www.nabble.com/file/p20231967/output_LS.png output_LS.png 

Would it be possible that I post the fixed and moving images here? They are
in Analyze format. Again, the registration code is exactly the same as
DeformableRegistration15.cxx (from ITK version 3.8).

Thanks very much!

Pinpress




Hi Pinpress,

when you do the affine + B-spline registration you have to set the
affine result in the bulk transform of the B-spline. You have to do this
also when you compute the displacement field. If you forget to do that
than you will only compute the displacement of the B-spline part. I can
imagine that this part is almost zero, since the match between the
larger and smaller circle can be captured by an affine transformation
only. 

Can you check that you did set the affine transform in the bulktransform
of the B-spline?

I find it hard to judge the images you uploaded. Can you easily
construct images where the deformation field is evaluated a coarser
grid, with larger arrows?

The error seems to be a bug in your code somewhere. If you post your
code we may be able to track it down.

Marius


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