[Insight-users] Direction of the transform in the registration framework

[Anja Ende]

Hello,

This is discussed in the software guide but I wam having a bit of
trouble understanding why the transform that is optimized is the one
that takes you from points fixed image to points in moving imge.

The guide says:

"What tends to create confusion is the fact that when the Transform
shifts a point on the positive X direction, the visual effect of this
mapping, once the moving image is resampled, is equivalent to manually
shifting the moving image along the negative X direction".

I am struggling to see how this is. Say as an example,the optimized
transformation from fixed to moving image is a simple translation by 5
mm. So, my deformation field is where every point is shifted by 5 mm.
How does the resampler use this information and how is equivalant to
shifting the moving image by -5 mm? If someone could help me
understand what happens say at a chosen point..it would help me a lot.
I think I am not understanding how the resampler would effect the
moving image given that the transformation is:

1 0 0 5
0 1 0 0
0 0 1 0
0 0 0 1

I would be really grateful if someone could illustrate this to me...

Many thanks!

Cheers,

Anja