[ITK-dev] Optimizing composite transforms and center of transform

[Nicholas Tustison]

Hi Brad,

I apologize for the delayed response.  I’m still catching up on my 
workload after moving to CA.  We might want to talk to Luis as it 
was my understanding that the “center” component of the linear 
transforms might be a carry-over from all the “Centered” transforms, 
e.g., 

http://www.itk.org/Doxygen/html/classitk_1_1CenteredAffineTransform.html

which, if I remember correctly, Luis said were somewhat sub optimally 
conceived but this was such a long time ago that I might be completely
misremembering.  However, fixing the center for all transforms within 
a composite transform is certainly not necessary within the specified
framework.  Rather, the matrix and offset are updated with the “Center”
being updated implicitly.

Nick



On Jul 24, 2014, at 7:27 AM, Bradley Lowekamp <blowekamp at mail.nih.gov> wrote:

> Hello,
> 
> There are a lot of transforms involved in the new registration framework.
> 
> I am trying to figure out what the implications for the fix parameters of the transform "Center" ( ie center of rotation/scaling ) are when combined with composite transforms and the fixed/moving/registration coordinate frames...
> 
> Based on how the transforms are composed it seems necessary to set the  fix "Center" for subsequent transformations. Additionally, I am unsure how one would "improve" ( poorly defined? ) the center for a subsequent transform ie Affine after a similarity...
> 
> Are there some documented guidance or figures to help with this issue?
> Do we have a comprehensive diagram of these transforms?
> 
> Thanks,
> Brad
>