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      Use a FITS header to convert astronomical to pixel coordinates


      Use an image header to compute X and Y positions, given the
      RA and Dec (or longitude, latitude) in decimal degrees.

Calling Sequence

      ADXY, HDR ;Prompt for Ra and DEC
      ADXY, hdr, a, d, x, y, [ /PRINT, ALT= ]


      HDR - FITS Image header containing astrometry parameters

Optional Inputs

      A - Right ascension in decimal DEGREES, scalar or vector
      D - Declination in decimal DEGREES, scalar or vector
      If A and D are not supplied, user will be prompted to supply
      them in either decimal degrees or HR,MIN,SEC,DEG,MN,SC format.

Optional Output

      X - row position in pixels, same number of elements as A and D
      Y - column position in pixels
      X and Y will be in standard IDL convention (first pixel is 0) and not
      the FITS convention (first pixel is 1). As in FITS an integral
      value corresponds to the center of a pixel.

Optional Keyword Input

      /PRINT - If this keyword is set and non-zero, then results are displayed
              at the terminal.
      ALT - single character 'A' through 'Z' or ' ' specifying an alternate
            astrometry system present in the FITS header. The default is
            to use the primary astrometry or ALT = ' '. If /ALT is set,
            then this is equivalent to ALT = 'A'. See Section 3.3 of
            Greisen & Calabretta (2002, A&A, 395, 1061) for information about
            alternate astrometry keywords.

Operational Notes

      If less than 5 parameters are supplied, or if the /PRINT keyword is
      set, then the X and Y positions are displayed at the terminal.
      If the procedure is to be used repeatedly with the same header,
      then it would be faster to use AD2XY.

Procedures Called


Revision History

      W. Landsman HSTX January, 1988
      Use astrometry structure W. Landsman January, 1994
      Changed default ADSTRING format W. Landsman September, 1995
      Check if latitude/longitude reversed in CTYPE keyword W. L. Feb. 2004
      Added ALT keyword W. Landsman September 2004
      Work for non-spherical coordinate transformation W. Landsman May 2005
      More informative error message if astrometry missing W.L. Feb 2008
      Cosmetic updates W.L. July 2011

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