ARROWS

      To display "weathervane" directional arrows on an astronomical image

      Overlays a graphic showing orientation of North and East.

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

       h - FITS or STSDAS header array, must include astrometry

       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

       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 that the arrows and NE letters should be.  Default
                    value is !P.COLOR
       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

       none

       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".

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

       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
       Converted to IDL V5.0   W. Landsman   September 1997
       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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