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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).
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.

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