Select planes 1 in n from a 3D object
      resetting voxel size to suit and
      writing the new object to standard output
      Options are:
      -f#       first plane (def: 0)
      -l#       last plane (less than first = > all, def: -1)
      -n#       step (def: 3)
      -h       Help - prints this usage message
      -v       Verbose operation