When the user chooses "Saturn barycentric" or "Saturn geocentric"
as the origin and "Geographic" as the coordinate system, the output
will include three longitude values.  The three values are labeled as
"WL (IAU)", "WL (SLS2)",  and "WL (SLS3)".  The first value [WL (IAU)]
is based on a longitude system described here:

      Seidelmann et al.:2002, "Report on the IAU/IAG Working Group
      on Cartographic Coordinates and Rotational Elements of the
      Planets and Satellites: 2000", CELESTIAL MECHANICS AND
      DYNAMICAL ASTRONOMY 82: 83-110, 2002.

   The second value [WL (SLS2)] is based on a longitude system
described here:

      Kurth et al.:2007, "A Saturnian Longitude System Based on a
      Variable Kilometric Radiation Period", GEOPHYS. RES.
      LETT. 34, L02201, doi:10.1029/2006GL028336, Jan. 2007.

   The third value [WL (SLS3)] is based on a longitude system
described here:

      Kurth et al.:2007, "An Update to a Saturnian Longitude
      System Based on Kilometric Radio Emissions", J. GEOPHYS.
      RES., submitted, Oct. 10, 2007.

   Note that all three values are considered west longitude (WL).

   The SLS2 longitude system is only valid for this time period:

      1 January 2004 to 28 August 2006.

   The SLS3 longitude system is only valid for this time period:

      1 January 2004 through 10 August 2007.

   If the user chooses a time outside these time periods, a fill
value of -1 will be used in the output.