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GEO2ECI

GEO2ECI

## Purpose

Convert geographic spherical coordinates to Earth-centered inertial coords

## Explanation

Converts from geographic spherical coordinates [latitude, longitude,
altitude] to ECI (Earth-Centered Inertial) [X,Y,Z] rectangular
coordinates. JD time is also needed.
Geographic coordinates are in degrees/degrees/km
Geographic coordinates assume the Earth is a perfect sphere, with radius
ECI coordinates are in km from Earth center.

## Calling Sequence

ECIcoord=geo2eci(gcoord,JDtime)

## Input

gcoord: geographic [latitude,longitude,altitude], or a an array [3,n]
of n such coordinates
JDtime: Julian Day time, double precision. Can be a 1-D array of n
such times.

None

## Output

a 3-element array of ECI [X,Y,Z] coordinates, or an array [3,n] of
n such coordinates, double precision

None

## Procedures Used

CT2LST - Convert Local Civil Time to Local Mean Sidereal Time

## Examples

IDL> ECIcoord=geo2eci([0,0,0], 2452343.38982663D)
IDL> print,ECIcoord
-3902.9606 5044.5548 0.0000000
(The above is the ECI coordinates of the intersection of the equator and
Greenwich's meridian on 2002/03/09 21:21:21.021)

## Modification History

Written by Pascal Saint-Hilaire (shilaire@astro.phys.ethz.ch)
on 2002/05/14

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