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      Draw an arc bar on an image showing the astronomical plate scale

Calling Sequence

      ARCBAR, hdr, arclen,[ COLOR= , /DATA, LABEL= , /NORMAL, POSITION=,
                              /SECONDS, SIZE=, THICK=, FONT= ]


      hdr - image FITS header with astrometry, string array

Optional Input

      arclen - numeric scalar giving length of bar in arcminutes (default)
              or arcseconds (if /SECONDS is set). Default is 1 arcminute

Optional Keyword Inputs

      COLOR - name or integer scalar specifying the color to draw the arcbar
              See cgColor for a list of available color names
      /DATA - if set and non-zero, then the POSITION keyword and the arc
              length is given in data units
      LABEL - string giving user defined label for bar. Default label is size
              of bar in arcminutes
      /NORMAL - if this keyword is set and non-zero, then POSITION is given in
              normalized units
      POSITION - 2 element vector giving the (X,Y) position in device units
              (or normalized units if /NORMAL is set, or data units if /DATA
              is set) at which to place the scale bar. If not supplied,
              then the user will be prompted to place the cursor at the
              desired position
      /SECONDS - if set, then arlen is specified in arcseconds rather than
      SIZE - scalar specifying character size of label, default = 1.0
      THICK - Character thickness of the label, default = !P.THICK
      FONT - scalar font graphics keyword (-1,0 or 1) for text


      Suppose one has an image array, IM, and FITS header, HDR, with
      astrometry. Display the image and place a 3' arc minute scale bar
      at position 300,200 of the current image window
      IDL> cgimage, IM, /scale,/save ;Use /SAVE to set data coordinates
      IDL> arcbar, HDR, 3, pos = [300,200],/data


      When using using a device with scalable pixels (e.g. postscript)
      the data coordinate system must be established before calling ARCBAR.
      If data coordinates are not set, then ARCBAR assumes that the displayed
      image size is given by the NAXIS1 keyword in the FITS header.

Procedure Calls


Revison History

      written by L. Taylor (STX) from ARCBOX (Boothman)
      modified for Version 2 IDL, B. Pfarr, STX, 4/91
      New ASTROMETRY structures W.Landsman, HSTX, Jan 94
      Recognize a GSSS header W. Landsman June 94
      Added /NORMAL keyword W. Landsman Feb. 96
      Use NAXIS1 for postscript if data coords not set, W. Landsman Aug 96
      Fixed typo for postscript W. Landsman Oct. 96
      Account for zeropoint offset in postscript W. Landsman Apr 97
      Added /DATA, /SECONDS keywords W. Landsman July 1998
      Use device-independent label offset W. Landsman August 2001
      Allow font keyword to be passed. T. Robishaw Apr. 2006
      Remove obsolete TVCURSOR command W. Landsman Jul 2007
      Use Coyote Graphics W. Landsman February 2011
      Fix problem using data coordinates when not in postscript
                W. Landsman January 2013

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