COORDS finds the right ascension and declination for each star in a photometry file. At least three of the stars must have had their R.A. and Declination. entered in MARKSTAR or in MODPHOT. The coordinates for the standards must all be at the same epoch. (One day we will have a precession program.)
COORDS works by solving a least-square relation between the rectangular coordinates on the image (i.e., row and column) and the spherical coordinates on the sky. The program calculates the coordinates for every star in the photometry file based on the standard positions you have entered, including the standard stars. The input positions, calculated positions, and difference in seconds of time for the standards will be displayed on your terminal. The program will then print the positions of the standards.
The difference between the input and the calculated positions should be small and evenly distributed about zero. If not, one or more of your input coordinates is possibly wrong. Use MODPHOT to change that coordinate, and try again. Note that the difference is in seconds of arc for both the declination and the right ascension.
If you want to save the coordinates computed by the MODPHOT command, you must use the 'SAVE PHOT=filename' command.
The output of COORDS can be redirected. See HELP REDIRECT for information about the redirection mechanism.