[Insight-users] about source and target landmarks

[Luis Ibanez]

Hi Monica,

ITK Transforms are intended for performing image registration.

The final goal of image registration is to be able to map the
Moving image into the coordinate system of the Fixed image.

This is done by visiting each pixel of the *Fixed* image and
finding the corresponding location of this pixel in the Moving
image.  If we don't visit all the pixels in the Fixed image,
then the resampled Moving image will contain holes.

Since the operation that you need is to map the coordinates
of Fixed image pixels onto the reference system of the Moving
image, then you need a transform that will use as input points
the ones on the reference system of the Fixed image and as
target points the ones on the reference system of the Moving
image.

This same mapping direction is done consistently for *all*
ITK registration and resampling classes.

Please read the Chapter on image resampling from the ITK
Software Guide.

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


Section 6.7.1, pdf-page 199-210.

This will help to clarify the Transform direction to you.

In summary:  When you say that you are registering the
Moving image TO the Fixed image, in practice that means
that you are computing a transform for mapping coordinate
from the Fixed image into coordinates of the Moving image.



Please let us know if you have further questions,



   Thanks


      Luis



------------------------
Monica Lumbardi wrote:

> Hi,
>  
> I'm working with Landmarkwarping2 on 3D Analyze images and I found Luis 
> explanation about the DeformationField:
>  
> http://public.kitware.com/pipermail/insight-users/2003-February/002646.html
>  
> If I have points file (with 1 source and 1 target landmark): 
>  
> 37.94 107.15 61.54 37.94 107.15 44.4
>  
> with first point beeing source landmark (37.94 107.15 61.54) and second 
> point beeing target landmark (37.94 107.15 44.4 ), I still don't 
> understand why on the transformed moving image the target ponts is 
> moving toward the source point. Which it is opposite of what I would 
> have expected.
>  
> Luis, can you please clarify this?
>  
> Thanks
>  
> Monica
>  
> 
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