Measure the small offsets between images.

% lil_shifts list1 1 255 0.071  

arg1 = filename for list of FITS images
arg2 = low display level (z1)
arg3 = high display level (z2)
arg4 = plate scale 

# Process a list of images that have small x,y shifts
# The basic step of this routine are:
#  1) Operate on a set of images in a list
#  2)  Display the first image and mark a target
#       - use ds9_open and ds9_view for this
#  3) With the first image build a local "id.objects" file.
#       - ise obj_id_build.sh
#  4) Use the "id.objects" to compute MIDO parameters
#     for all images in the input list.
#       - use mido.sh
#  5) After all images are measure, compute the shift
#     of each image.
#       - use xy_shift_stats.sh