Does the -regress_censor_motion in afni_proc.py meant Framewise displacement (FD)?
If so, it is calculated by the absolute value of derivatives of the six realignment parameters or RMS of those?
AFNI has used the Euclidean norm, sqrt(sum squares), since long before FD was suggested, and it still does. RMS is slightly different, too, which is scaled down by (sqrt of) the number of terms.
Note that FD does not make so much sense to use as a distance measure in any case. For example, the distance between points at (0,0,0) and (1,1,1) should be sqrt(3)~=1.73, not 3.
So which value I used for the Euclidean norm would be appropriate?