[Insight-users] Registration: X translation is always wrong

[itkvtk123 at gmx.net]

I'm trying to register two 256px images with 1mm spacing and I expect +- 0.175 radian in rotation and +- 10 mm in translation.
So I set the scales to

rotationScale = 1.0
translationScale = 0.00175

I set the initial search radius of OnePlusOne optimizer to 0.175, so we should be searching for values in a rotation interval of +- 0.175 radian and a translation interval of +-100 mm.

In my test case the real offset is 25mm in X, 25mm in Y and 0.087 radian in rotation.


The OnePlusOneOptimizer (initial search radius 0.175, epsilon 1.0) results in:

-0.579999 for X (should be -25.0)
-31.3951 for Y (should be -25.0)
0.0869 for Rotation (should be 0.087)

So Rotation is right, Y is quite right and X is totally wrong.



When I do the same scenario with Gradient Descent (Max step length = 0.175 (is 100mm) Min step length = 0.00175 (is 1mm)) I get the following results:

-10.8652 for X (should be -25.0)
-26.6043 for Y (should be -25.0)
0.0872 for Rotation (should be 0.087)

Again, Y is quite right, Rotation is correct and X is wrong.


In the Optimizer History you can see that values for Y rise always faster than values for X (regardless which optimizer).
But why? They have the same scale! Pixel spacing is also the same for X and Y in the image.

Thank you.
-- 
GRATIS für alle GMX-Mitglieder: Die maxdome Movie-FLAT!
Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01