NAME:
  wfc3_smear
 PURPOSE:   (one line only)
  Compute a smear kernel for a star while tracking a solar system object
 DESCRIPTION:
 CATEGORY:
  Astrometry
 CALLING SEQUENCE:
  wfc3_smear,data,ocode,x,y,kernel
 INPUTS:
  data   - anonymous structure produced by rdwfc3.pro
  ocode  - NAIF object code
  x      - x position of source
  y      - y position of source
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  kernel - smear kernel
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
  This only works with spice kernel orbits.
 PROCEDURE:
 MODIFICATION HISTORY:
  2020/06/24, Written by Marc W. Buie, Southwest Research Institute