interpretation of .aff file in dti-tk

[mrbago]

Hi all,
Thanks in advance for you help. I want to be able to use the
rotation matrix from the dti-tk rigid registration to rotate gradient
vectors. From what I can tell the Matrix and Vector in the .aff file
are defined such that:

i = Matrix * r + Vector

where r is a point in the reference image and i is a point in the
input image. Is this correct? Is there any documentation on the
specific interpretation of Matrix and Vector somewhere? I've started
to reverse engineer it, but it I'd prefer not to waste my time if it's
documented somewhere.

Thanks
Bago

[Hui Zhang]

Hi Bago,

That's correct. Just remember that it is an inverse transform. The figure in the following tutorial demonstrates this concept pictorially:

http://dti-tk.sourceforge.net/pmwiki/pmwiki.php?n=Documentation.OptionspostReg

Gary