[ITK] [ITK-users] AffineTransform to 4x4 matrix...again maybe

[Bradley Lowekamp]

Hello,

That looks pretty close, but I think CRM[12,13,14] should be -GetCenter(), with the negative there.  Then the TM should be applied last, using your original notation with the previously mentioned correction I'd expect this to be correct:

OGLM = TM * InvCRM * Rot * CRM

Hope that helps,
Brad

[1] http://www.itk.org/Doxygen/html/classitk_1_1MatrixOffsetTransformBase.html

On Aug 5, 2014, at 5:26 AM, vincent ngai <vincent.ngai at gmail.com> wrote:

> Hi all, apologies if this has been asked before, I googled the above but only got 4x4 -> AffineTransform and not the other way around.
> 
> I need to get the output of an AffineTransform after registration to my OpenGL renderer. 
> 
> From what I understand, the AffineTransform is composed of a Rotation, Center of Rotation and Translation.
> 
> So would the following sequence of 4x4 transformation be correct?
> 
> OGLM = InvCRM * Rot * CRM * TM
> 
> where
> 
> CRM      = 4x4 identity matrix with indices [ 12, 13, 14] set to XYZ value of GetCenter()
> InvCRM  = Inverse of CRM
> Rot        = 4x4 Identity matrix with 3x3 set to the rotation parameters
> TM        = 4x4 identity matrix with indicies[ 12, 13, 14 ] set to the translation parameters
> 
> Essentially:
>  
> 1) translate center to origin
> 2) perform rotation
> 3) translate back to where we were
> 4) slap on translation
> 
> I am doing the above, but for some reason the translation does not match up. The rotation seems fine.
> -- 
> Regards,
> Vincent
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