NAME:
    ringprof
 PURPOSE: (one line)
    Compute a surface brightness profile.
 DESCRIPTION:

 CATEGORY:
  CCD data processing
 CALLING SEQUENCE:
    ringprof, image, xcen, ycen, rmax, dr, skyback, rout, iout
 INPUTS:
    image      : CCD image array.
    xcen, ycen : Coordinates of center.
    rmax       : Maximum radius for profile.
    dr         : Incremental value of radius.
    skyback    : Sky background.
 OPTIONAL INPUT PARAMETERS:

 KEYWORD PARAMETERS:

 OUTPUTS:
    rout : Radius vector of length rmax/dr+1.
    rout : Counts vector of length rmax/dr+1.

 COMMON BLOCKS:

 SIDE EFFECTS:

 RESTRICTIONS:

 PROCEDURE:

 MODIFICATION HISTORY:
    Ported by Doug Loucks, Lowell Observatory, March 1993, from
    the C-language version written by Marc Buie.