[Insight-users] FW: How to convert VersorRigid3DTransform to vtkTransform

[Yu Qi]

Hi Luis,
Thanks for your suggestion.
I noticed the difference between SPM and ITK.

 
I have another question
Do you think the transform parameter obtained from ITK by using different interpolators will be exactly the same or not?
for example use linear interpolator and B-Spline interpolator.
 
Best regards,
Yu Qi
 

Luis Ibanez <luis.ibanez at kitware.com> 写道:

Hi Yu,

It seems that thanks to your detailed description, you
provided the answer to your problem in your own message:


"> But SPM integrates spacing info into the rotation 3X3 matrix."


This seems to be the key to the problem that you are facing.



ITK *DOES NOT* incorporates the compensation for pixel spacing
into the Transform that results from the registration. The
reason is that image registration in ITK is done in physical
units, not in the image grid.

You will find a detailed description of this issue in the
ITK Software Guide

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


Section 8.3.2 "Registration is done in Physical Space"
pdf-page 319.




Regards,



Luis



----------------------------------
Yu Qi wrote:

> Hi Luis,
> 
> Thank you!
> 
> In SPM, the equations to transform the moving image is as follows
> x1=R00*x+R01*y+R02*z+Trans0
> y1=R10*x+R11*y+R12*z+Trans1
> z1=R20*x+R21*y+R22*z+Trans2
> 
> But SPM integrates spacing info into the rotation 3X3 matrix.
> 
> I compared the result from ITK and the one from SPM,
> I found ITKrotation*ITKspacing is very close to the Ratation matrix in 
> SPM and the translations are also very close.
> 
> But I can not obtain a good transform in SPM using ITK result.
> Do you think there will be other reasons for this? like the 
> interpolation method (default setting in SPM is linear and I use linear 
> in ITK)?
> 
> Best regards,
> Yu Qi
> 
> 






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