GEODETIC2GEO

       Convert from geodetic (or planetodetic) to geographic coordinates

       Converts from geodetic (latitude, longitude, altitude) to geographic
       (latitude, longitude, altitude).  In geographic coordinates, the
       Earth is assumed a perfect sphere with a radius equal to its equatorial
       radius. The geodetic (or ellipsoidal) coordinate system takes into
       account the Earth's oblateness.
       Geographic and geodetic longitudes are identical.
       Geodetic latitude is the angle between local zenith and the equatorial
       plane.   Geographic and geodetic altitudes are both the closest distance
       between the satellite and the ground.
       The PLANET keyword allows a similar transformation for the other
       planets  (planetodetic to planetographic coordinates).
       The EQUATORIAL_RADIUS and POLAR_RADIUS keywords allow the
       transformation for any ellipsoid.
       Latitudes and longitudes are expressed in degrees, altitudes in km.
       REF: Stephen P.  Keeler and Yves Nievergelt, "Computing geodetic
       coordinates", SIAM Rev. Vol. 40, No. 2, pp. 300-309, June 1998
       Planetary constants from "Allen's Astrophysical Quantities",
       Fourth Ed., (2000)

       gcoord = geodetic2geo(ecoord, [ PLANET= ] )

       ecoord = a 3-element array of geodetic [latitude,longitude,altitude],
                or an array [3,n] of n such coordinates.

       PLANET = keyword specifying planet (default is Earth).   The planet
                may be specified either as an integer (1-9) or as one of the
                (case-independent) strings 'mercury','venus','earth','mars',
                'jupiter','saturn','uranus','neptune', or 'pluto'
       EQUATORIAL_RADIUS : Self-explanatory. In km. If not set, PLANET's value
                is used.   Numeric scalar
       POLAR_RADIUS : Self-explanatory. In km. If not set, PLANET's value is
                 used.   Numeric scalar

       a 3-element array of geographic [latitude,longitude,altitude], or an
         array [3,n] of n such coordinates, double precision
       The geographic and geodetic longitudes will be identical.

       None

       IDL> geod=[90,0,0]  ; North pole, altitude 0., in geodetic coordinates
       IDL> geo=geodetic2geo(geod)
       IDL> PRINT,geo
       90.000000       0.0000000      -21.385000
       As above, but the equivalent planetographic coordinates for Mars
       IDL> geod=geodetic2geo(geod,PLANET='Mars');
       IDL> PRINT,geod
       90.000000       0.0000000      -18.235500

       Written by Pascal Saint-Hilaire ([email protected]),
                  May 2002
       Generalized for all solar system planets by Robert L. Marcialis
               ([email protected]), May 2002
       Modified 2002/05/18, PSH: added keywords EQUATORIAL_RADIUS and
                POLAR_RADIUS

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