ADXY

       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.

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

       HDR - FITS Image header containing astrometry parameters

       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.

       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.

       /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.

       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.

       AD2XY, ADSTRING(), EXTAST, GETOPT(), TEN()

       W. Landsman                 HSTX          January, 1988
       Use astrometry structure   W. Landsman   January, 1994
       Changed default ADSTRING format   W. Landsman    September, 1995
       Converted to IDL V5.0   W. Landsman   September 1997
       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

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