ADSTRING

       Return RA and Dec as character string(s) in sexigesimal format.

       RA and Dec may be entered as either a 2 element vector or as
       two separate vectors (or scalars).  One can also specify the precision
       of the declination in digits after the decimal point.

       result = ADSTRING( ra_dec, precision, /TRUNCATE )
               or
       result = ADSTRING( ra,dec,[ precision, /TRUNCATE ] )

       RA_DEC - 2 element vector giving the Right Ascension and declination
               in decimal degrees.
                     or
       RA     - Right ascension in decimal degrees, numeric scalar or vector
       DEC    - Declination in decimal degrees, numeric scalar or vector

       PRECISION  - Integer scalar (0-4) giving the number of digits after the
               decimal of DEClination.   The RA is automatically 1 digit more.
               This parameter may either be the third parameter after RA,DEC
               or the second parameter after [RA,DEC].  It is not available
               for just DEC.   If no PRECISION parameter is passed, a
               precision of 1 for both RA and DEC is returned to maintain
               compatibility with past ADSTRING functions.    Values of
               precision larger than 4 will be truncated to 4.    If
               PRECISION is 3 or 4, then RA and Dec should be input as
               double precision.

       /TRUNCATE - if set, then the last displayed digit in the output is
               truncated in precision rather than rounded.   This option is
               useful if ADSTRING() is used to form an official IAU name
               (see http://vizier.u-strasbg.fr/Dic/iau-spec.htx) with
               coordinate specification.   The IAU name will typically be
               be created by applying STRCOMPRESS/REMOVE) after the ADSTRING()
               call, e.g.
              strcompress( adstring(ra,dec,0,/truncate), /remove)   ;IAU format

       RESULT - Character string(s) containing HR,MIN,SEC,DEC,MIN,SEC formatted
               as ( 2I3,F5.(p+1),2I3,F4.p ) where p is the PRECISION
               parameter.    If only a single scalar is supplied it is
               converted to a sexigesimal string (2I3,F5.1).

       (1) Display CRVAL coordinates in a FITS header, H
       IDL> crval = sxpar(h,'CRVAL*')  ;Extract 2 element CRVAL vector (degs)
       IDL> print, adstring(crval)     ;Print CRVAL vector sexigesimal format
       (2)  print,adstring(30.42,-1.23,1)  ==>  ' 02 01 40.80  -01 13 48.0'
            print,adstring(30.42,+0.23)    ==>  ' 02 01 40.8   +00 13 48.0'
            print,adstring(+0.23)          ==>  '+00 13 48.0'
       (3) The first two calls in (2) can be combined in a single call using
           vector input
              print,adstring([30.42,30.42],[-1.23,0.23], 1)

       FSTRING(), RADEC, SIXTY()

       Written   W. Landsman                      June 1988
       Addition of variable precision and DEC seconds precision fix.
       ver.  Aug. 1990 [E. Deutsch]
       Output formatting spiffed up       October 1991 [W. Landsman]
       Remove ZPARCHECK call, accept 1 element vector  April 1992 [W. Landsman]
       Call ROUND() instead of NINT()    February 1996  [W. Landsman]
       Check roundoff past 60s           October 1997   [W. Landsman]
       Work for Precision =4             November 1997  [W. Landsman]
       Converted to IDL V5.0   W. Landsman 24-Nov-1997
       Major rewrite to allow vector inputs   W. Landsman  February 2000
       Fix possible error in seconds display when Precision=0
                               P. Broos/W. Landsman April 2002
       Added /TRUNCATE keyword, put leading zeros in seconds display
                               P. Broos/W. Landsman September 2002
       Hours values always less than 24   W. Landsman September 2002
       Fix zero declinations for vector processing W. Landsman February 2004
       Fix possible problem in leading zero display W. Landsman June 2004

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