NAME:
  wcsarrows
 PURPOSE:   (one line only)
  Draw sky-plane orientation arrows on an image based on WCS information
 DESCRIPTION:
 CATEGORY:
  Astronomy
 CALLING SEQUENCE:
  wcsarrows,info
 INPUTS:
  info - anonymous structure that carries the astrometric information.
            You can provide a structure returned from the Astron library
            (extast) or from my library (astinfo).
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  X - x location of vertex of drawn arrows (default=upper right)  DEVICE COORDS
  Y - y location of vertex of drawn arrows (default=upper right)  DEVICE COORDS
  PA - position angle of one extra vector to draw, typically this is for
         denoting the projected north pole vector.  This angle is given in
         degrees east of north.  The default is to not draw this vector.
  LABEL - label for the extra vector, ignored if PA not specified.
            default = 'Np'
  NOPLOT - Flag, if set will do all the computations but skip the actual
             display.   This is useful if you want the ainfo structure
             but aren't plotting.
 OUTPUTS:
  All output is in the form of plotted information on the current window
 KEYWORD OUTPUT PARAMETERS:
  AINFO - anonymous structure that contains information computed here
            x: device coordinate of center of compass
            y: device coordinate of center of compass
            north: angle for North vector, in degrees (0 is to the right)
            east:  angle for East vector, in degrees
            pscale: Image scale in arcsec/pixel, computed in center of image
            pang:  angle for extra vector, if not provided this is the
                      the same as north.
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2015/10/07, Written by Marc W. Buie, Southwest Research Institute
  2017/04/20, MWB, added pscale to output structure
  2017/07/05, MWB, added support for use of !order for image orientation.
  2021/01/18, MWB, added NOPLOT keyword
  2021/02/01, MWB, fixed bug when using NOPLOT keyword
  2021/03/31, MWB, fixed incorrect plate scale calculation for my solutions