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      To display "weathervane" directional arrows on an astronomical image


      Overlays a graphic showing orientation of North and East.

Calling Sequence

      ARROWS,h, [ xcen, ycen, ARROWLEN= , CHARSIZE= COLOR= , /DATA
                              FONT=, /NORMAL, /NOTVERTEX, THICK= ]


      h - FITS header array, must include astrometry

Optional Inputs

      xcen,ycen - numeric scalars, specifying the center position of
arrows. Position in device units unless the /NORMALIZED
keyword is specified. If not supplied, then ARROWS
will prompt for xcen and ycen

Optional Keyword Inputs

      arrowlen - length of arrows in terms of normal Y size of vector-drawn
                    character, default = 3.5, floating point scalar
      charsize - character size, default = 2.0, floating point scalar
      color - color name or number for the arrows and NE letters. See
                cgCOLOR() for a list of color names.
      Data - if this keyword is set and nonzero, the input center (xcen,
                ycen) is understood to be in data coordinates
      font - IDL vector font number (1-20) to use to display NE letters.
                For example, set font=13 to use complex italic font.
      NotVertex - Normally (historically) the specified xcen,ycen indicated
                  the position of the vertex of the figure. If this
                  keyword is set, the xcen,ycen coordinates refer to a sort
                  of 'center of mass' of the figure. This allows the
                  figure to always appear with the area irregardless of
                  the rotation angle.
      Normal - if this keyword is set and nonzero, the input center
                (xcen,ycen) is taken to be in normalized coordinates. The
                default is device coordinates.
      thick - line thickness, default = 2.0, floating point scalar




      Draw a weathervane at (400,100) on the currently active window,
      showing the orientation of the image associated with a FITS header, hdr
      IDL> arrows, hdr, 400, 100


      Uses EXTAST to EXTract ASTrometry from the FITS header. The
      directions of North and East are computed and the procedure
      ONE_ARROW called to create the "weathervane".

Procedures Used

      GETROT - Computes rotation from the FITS header
      ONE_ARROW - Draw a labeled arrow

Revison History

      written by B. Boothman 2/5/86
      Recoded with new procedures ONE_ARROW, ONE_RAY. R.S.Hill,HSTX,5/20/92
      Added separate determination for N and E arrow to properly display
        arrows irregardless of handedness or other peculiarities and added
        /NotVertex keyword to improve positioning of figure. E.Deutsch 1/10/93
      Added /DATA and /NORMAL keywords W. Landsman July 1993
      Recognize GSSS header W. Landsman June 1993
      Added /FONT keyword W. Landsman April 1995
      Modified to work correctly for COLOR=0 J.Wm.Parker, HITC 1995 May 25
      Work correctly for negative CDELT values W. Landsman Feb. 1996
      Use GETROT to compute rotation W. Landsman June 2003
      Restored /NotVertex keyword which was not working after June 2003 change
                  W. Landsman January 2004

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