[Freesurfer] Search angle limitation in the flirt registration

Hi freesurfer developers and users,

I'm writing to ask about the search angle limitation (--searchrx, -- searchry and --searchrz) in the flirt function. I use the search angle option a lot for limited angle search, which usually generate a better registration result compared with the broad angle search. But I still don't quite understand how rx,ry and rz are defined and how negative and positive angles affect the result. Because sometimes I find the result after the angle limitation does not align well with my expectation of rotation angle.

Thank you for your help,

Yixin Ma

Brain Image and Analysis Center

Duke university