The gastro program determines the astrometric transformation for an image based on the cmp/smp file. This file contains both the table of object data and the complete image FITS header. Using the header astrometric information as a starting point, gastro loads the reference astrometry objects appropriate for the region and determines the matching objects between the image and the reference. These objects are used, with iteration to improve the sample, to determine the astrometric transformation with up to 3rd order polynomials.

 gastro filtname.cmp
   -p (photcode)
   -coords (ra) (dec)