[Insight-users] Fixed and moving images in translation registration method example?

[Luis Ibanez]

Hi Motes,

You are making the common mistake of deriving conclusions
based on the visual display of the images but without adding
a coordinate system display to it.

You need to draw on top of:
http://37133.vs.webtropia.com/apache2-default/test/translate.jpg

the position of the image origin and the arrows that indicate the
positive direction of the X and the Y axis (as defined by ITK
when the images are read).



You will find, that in your display, the positive direction of the
"Y" axis is pointing downward.

You should use a viewer that uses the same orientation display
as ITK, and not rely on the basic viewers that are provided by
your operating system.


     Regards,


           Luis


-------------------
On Fri, Nov 13, 2009 at 5:05 PM, motes motes <mort.motes at gmail.com> wrote:
> In the image registration examples folder there is the file:
>
> ImageRegistration1.cxx
>
> which performs a registration using a translation transform.
>
> As fixed image I use:
>
>      BrainProtonDensitySliceBorder20.png";
>
> and as moving image I use:
>
>      BrainProtonDensitySliceShifted13x17y.png";
>
> located in InsightToolkit-3.12.0\Examples\Data. They look like this:
>
> http://37133.vs.webtropia.com/apache2-default/test/translate.jpg
>
> The resulting parameters are:
>
> Translation X = 12.9959
> Translation Y = 17.0001
>
> But should the result not be:
>
> Translation X = 12.9959
> Translation Y = -17.0001
>
> ?
>
> Based on the itkSoftwareGuide the transform maps from the fixed image
> to the moving image. The black circle represents a point in the
> fixed image:
>
> black_circle = (x,y)
>
> now to get to the corresponding point, marked with a red_circle, in
> the moving image (direction of the transform) one needs to do:
>
> red_circle = (x+12.9959, y-17.0001)
>
> and NOT:
>
> red_circle = (x+12.9959, y+17.0001)
>
> In my twisted world the correct parameters should therefore be:
>
> Translation X = 12.9959
> Translation Y = -17.0001
>
>
> I know this is extremly basic but for some reason I still don't understand this.
>
>
> In the itkSoftwareGuide page 321 it actually looks correct, but its
> not how the images look in the \Examples\Data folder - even more
> confusing.
>
> Hope someone can clarify this.
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