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GEODETIC2GEO

GEODETIC2GEO

Name


      GEODETIC2GEO

Purpose


      Convert from geodetic (or planetodetic) to geographic coordinates

Explanation


      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)

Calling Sequence


      gcoord = geodetic2geo(ecoord, [ PLANET= ] )

Input


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

Optional Keyword Input


      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

Output


      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.

Common Blocks


      None

Examples



      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

Modification History


      Written by Pascal Saint-Hilaire (shilaire@astro.phys.ethz.ch),
                  May 2002
      Generalized for all solar system planets by Robert L. Marcialis
              (umpire@lpl.arizona.edu), May 2002
      Modified 2002/05/18, PSH: added keywords EQUATORIAL_RADIUS and
                POLAR_RADIUS



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