Two 3dQwarp questions

AFNI Message Board
1

Hello AFNI friends -

I’ve been using auto_warp.py/3dQwarp quite a bit lately for both subject->atlas and within-subject (2 separate timepoints) registration, and I’m a big fan. I have some questions about the output however -

  1. In the anat.un.aff.qw_WARP.nii volume, what do the voxel values in each sub-brick (x_delta, y_delta, z_delta) refer to? Is it an arbitrary ‘shift’ value, or does it refer to a displacement in millimeters (or other units)? I’ve tried looking for an answer, and I can’t seem to find it.

  2. In the anat.un.aff.nii_WarpDrive.log file, what do the RMS and ITER values refer to? I initially thought the RMS was a ‘goodness-of-fit’ measure, but I don’t think that’s the case…

Thank you!
Pete

2

Hi Pete,

  1. Yes, those should be displacements in mm (from the destination
    to the source).

  2. RMS is more of a badness-of-fit measure, that should go down
    in the before vs. after values. It only applies to the affine
    part of the transformation, though, from 3dWarpDrive.

  • rick
3

Thank you Rick!