NAME: 
  limbcen
 PURPOSE: 
  Find center of body from centroid of limb points (Designed for Jupiter).
 DESCRIPTION:
 CATEGORY:
  CCD data processing
 CALLING SEQUENCE:
  limbcen,image,xcen,ycen,DISPLAY=display
 INPUTS:
  image   - Image (or cube) to find limb-centers for.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  DISPLAY - window number for optional display (not 0), default no display.
 OUTPUTS:
  xcen    - Centroided position in X
  ycen    - Centroided position in Y
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  94/08/16 - Written by Marc W. Buie, Lowell Observatory.