GEO2GEODETIC

       Convert from geographic/planetographic to geodetic coordinates

       Converts from geographic (latitude, longitude, altitude) to geodetic
       (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  (planetographic to planetodetic 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
       Planterary constants from "Allen's Astrophysical Quantities",
       Fourth Ed., (2000)

       ecoord=geo2geodetic(gcoord,[ PLANET=,EQUATORIAL_RADIUS=, POLAR_RADIUS=])

       gcoord = a 3-element array of geographic [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.
       POLAR_RADIUS : Self-explanatory. In km. If not set, PLANET's value is
                used.

      a 3-element array of geodetic/planetodetic [latitude,longitude,altitude],
        or an array [3,n] of n such coordinates, double precision.

       None

       Whereas the conversion from geodetic to geographic coordinates is given
       by an exact, analytical formula, the conversion from geographic to
       geodetic isn't. Approximative iterations (as used here) exist, but tend
       to become less good with increasing eccentricity and altitude.
       The formula used in this routine should give correct results within
       six digits for all spatial locations, for an ellipsoid (planet) with
       an eccentricity similar to or less than Earth's.
       More accurate results can be obtained via calculus, needing a
       non-determined amount of iterations.
       In any case,
          IDL> PRINT,geodetic2geo(geo2geodetic(gcoord)) - gcoord
       is a pretty good way to evaluate the accuracy of geo2geodetic.pro.

       Locate the geographic North pole, altitude 0., in geodetic coordinates
       IDL> geo=[90.d0,0.d0,0.d0]
       IDL> geod=geo2geodetic(geo); convert to equivalent geodetic coordinates
       IDL> PRINT,geod
       90.000000       0.0000000       21.385000
       As above, but for the case of Mars
       IDL> geod=geo2geodetic(geo,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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