NAME: centrod PURPOSE: (one line) Compute center of mass of an object aperture. DESCRIPTION: CATEGORY: CCD data processing CALLING SEQUENCE: centrod, image, xcen, ycen, radius, inradius, outradius, skyback, $ xbar, ybar, counts INPUTS: image : CCD image array. xcen, ycen : Center of window. radius : Radius of window. inradius : Inner radius of sky annulus. outradius : Outer radius of sky annulus. skyback : Sky background in counts per pixel. OPTIONAL INPUT PARAMETERS: KEYWORD PARAMETERS: ADDNEG : Flag, if set, the position is computed using both the moments of counts above and below the background. Default is to compute the position only using those image values greater than the sky background. OUTPUTS: xbar, ybar : Position of center of mass. counts : Mass of object in counts. COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: PROCEDURE: MODIFICATION HISTORY: Ported by Doug Loucks, Lowell Observatory, 1992 Oct, from the C- language version written by Marc Buie. 4/1/93, DWL, Added argument validation (badpar). 99/08/31, MWB, added ADDNEG keyword.