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

[Luis Ibanez]

Hi Yu,

No,
the transform will not be *exactly* the same.


Regards,


   Luis


-------------------
Yu Qi wrote:
> 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,
>      >
>     &g! t; 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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