NAME:
  astmark
 PURPOSE:   (one line only)
  Annotate a graphic by marking an astronomical source in an image
 DESCRIPTION:
 CATEGORY:
  Astronomy
 CALLING SEQUENCE:
  astmark,x,y
 INPUTS:
  x - position of object to mark
  y - position of object to mark
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  DATA - Flag, if set, positions are in data units (default if none specified)
  NORMAL - Flag, if set, positions are in normal coordinates
  DEVICE - Flaf, if set, positions are in device coordinates
  GAP - distance to skip from position to start of mark (default=10)
  LEN - length of mark (default=15)
  DANG - angle between the two marks (default=120), in degrees
  ROTANG - rotation angle of two-mark pattern, in degrees

  Recognizes all standard plot graphics keywords.

 OUTPUTS:
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2015/03/17