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      Draws an arrow labeled with a single character on the current device


      ONE_ARROW is called, for example, by ARROWS to create a
      "weathervane" showing the N-E orientation of an image.

Calling Sequence

      one_arrow, xcen, ycen, angle, label, CHARSIZE = , THICK = , COLOR =
                      ARROWSIZE=, FONT = ]

Input Parameters

    xcen, ycen = starting point of arrow, floating point scalars,
                In device coordinates unless /DATA or /NORMAL set
    angle = angle of arrow in degrees counterclockwise from +X direction
    label = single-character label (may be blank)

Optional Input Parameters

      ARROWSIZE = 3-element vector defining appearance of arrow.
              For device coordinates the default is [30.0, 9.0, 35.0],
              meaning arrow is 30 pixels long; arrowhead lines 9 pixels
              long and inclined 35 degrees from arrow shaft. For
              normalized coordinates the default is divided by 512., for
              data coordinates the default is multiplied by
              (!X.crange[1] - !X.crange[0])/512..
      CHARSIZE = usual IDL meaning, default = 2.0
      COLOR = name or number give the color to draw the arrow. See
            cgCOLOR for a list of color names.
      /DATA - If set, then the input position (xcen, ycen) and the ARROWSIZE
                lengths are interpreted as being in data coordinates
      FONT - IDL vector font number to use (1-20). For example, to write
              the 'N' and 'E' characters in complex script, set font=13
      /NORMAL - If set, then the input position (xcen, ycen) and the ARROWSIZE
                lengths are interpreted as being in normal coordinates
      THICK = usual IDL meaning, default = 2.0


      Draw an triple size arrow emanating from the point (212,224)
      and labeled with the character 'S'
      IDL> one_arrow,212,224,270,'S',charsize=3


      Calls one_ray to vector-draw arrow.

Modification History

      Written by R. S. Hill, Hughes STX Corp., 20-May-1992.
      Added font keyword, W.B. Landsman Hughes STX Corp. April 1995
      Modified to work correctly for COLOR=0 J.Wm.Parker, HITC 1995 May 25
      Add /NORMAL and /DATA keywords W.Landsman November 2006
      Work with Coyote graphics W. Landsman February 2011

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