[Insight-users] Re: transform : direction of the transform in the ITK registration framework.

[Luis Ibanez]

Hi Andrew,

Yes, the transform that you get from the registration process
is the one that maps points from the coordinate system of the
Fixed image into the coordinate system of the Moving image.

This is the *exact same* transform that you need to pass to the
ResampleImageFilter in order to resample your Moving image into
the reference system of the Fixed image.

This issue is a common source of confusion for newcomers to
the ITK registration framework, and for that reason is described
in great detail in the ITK Software Guide


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


at the very beginning of the "Image Registration" chapter.

Please read that Chapter and let us know if you have further
questions.


    Thanks


      Luis


===================
Andrew Li wrote:
> Hi, Luis:
> 
> After we get a transform from a registration module, we use it for
> resampling. Like:
> 	resampler->SetTransform        (transform);
> 
> In file itkResampleImageFilter.h, it says:
> 
> /** Set the coordinate transformation.
>    * Set the coordinate transform to use for resampling.  Note that this
>    * must be in index coordinates and is the output-to-input transform,
>    * NOT the input-to-output transform that you might naively expect.
>    * The default is itk::AffineTransform<TInterpolatorPrecisionType,
> ImageDimension>. */
>   itkSetConstObjectMacro( Transform, TransformType );
> 
> Does it mean that the transform we got from registration is actually a
> transform from the fixed image volume to the moving image volume?
> 
> Please let me know whether it is the case. Thanks.
> 
> -Andrew
>  
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