[Insight-users] Question about Euler2DTransform

[Luis Ibanez]

Hi Albert,


    mm, You are not doing your Homework...



You skipped the reading of the ITK Software Guide,
and the section on resampling.


The "apparent" use of an inverse transform is
explained in detail in the ITK Software Guide.


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


Section 6.9, "Geometric Transforms", in PDF page 252


     and


Section 8.3, "Direction of the Transform", in PDF page 359.

Figure 8.7 in page 358 has the answer to your question.



ITK applies resampling by visiting all the pixels in the
output image, and using your provided transform in order
to map these positions onto the input image.



   Regards,


     Luis


-------------------------
Albert Chitemyan wrote:
> 
> Hi,
>  
> Thanks for your answers.
> It seems to me, I realized:
> The Euler2DTransform applies transformation first rotating, then 
> translating, but resampler obtains output image by transforming output 
> image into the input image, i.e. applies backward transformation
>  
> Euler2DTransform  transformation
> [ x' ] = [ cos   -sin ] [ x ] + [Tx]
> [ y '] = [ sin    cos ] [ y ] + [Ty]
>  
> backward transformation
> [ x ]  = [ cos  -sin ] [ x' - Tx ]
> [ y ]  = [ sin   cos ] [ y' - Ty ]
>  
> i.e. first translating the point, then rotating
>  
> Am I right ?
>  
> Thanks
>  
> Albert
> 
> */Zachary Pincus <zpincus at stanford.edu>/* wrote:
> 
>     Remember that a resampler uses a backward transformation from points
>     in the destination to points in the source image. (As described in
>     the software guide.) With this in mind, is the Euler transform still
>     not working as described?
> 
>     Zach Pincus
> 
>     Program in Biomedical Informatics and Department of Biochemistry
>     Stanford University School of Medicine
> 
>     On Nov 21, 2005, at 11:34 PM, Albert Chitemyan wrote:
> 
>      > Hi,
>      >
>      > In ItkSoftwareGuide is written that in Euler2DTransform the
>      > rotation is applied first, followed by the translation. But in
>      > practice the opposite thig takes place. How can you explain it?
>      > Albert
>      >
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