rotation when using f3d_sym

[rijobro]

As noted in SyneRBI/SIRF#680, using the symmetric version of f3d causes a rotation of the registered image and the resulting transformations (deformations and displacements).

This can be seen by comparing outputs of:

reg_f3d -flo test.nii -ref test.nii -sym

and

reg_f3d -flo test.nii -ref test.nii

When testing with an image where nx!=ny!=nz, the symmetric results look even stranger. I wonder if this implies that some images are being iterated across in the wrong order. When square, this results in a rotation, and when non-square, this results in a striding error.

I'm attaching two screenshots. The first screenshot, with nx==ny!=nz, shows a rotation. The second, with nx!=ny!=nz shows the distortion.

For both screenshots, test is the input, and outSym and outNoSym are the registered images, with and without symmetric, respectively.

Square

Non-square