minc_displacement doesn't document what it's for

[gdevenyi]

Help is a bit sparse:

Command-specific options:
General options:
 -verbose:  print out extra information
 -clobber:  clobber existing files

Generic options for all commands:
 -help:     Print summary of command-line options and abort
 -version:  Print version number of program and exit

Usage: minc_displacement [options] input.mnc input.xfm output_grid.mnc
       minc_displacement -help

It looks to me based on reading the code, it creates a volume like "input.mnc" then reads in an xfm, and creates a combined grid transform based on the result of the total evaluation.

I see it also "keeps the displacement in the three cardinal directions" by taking a difference between (location?) of the original voxel and the new voxel? Is that correct?