GEO2ECI

     Convert geographic spherical coordinates to Earth-centered inertial coords

     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
       equal to its equatorial radius.
     ECI coordinates are in km from Earth center.

       ECIcoord=geo2eci(gcoord,JDtime)

       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

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

       None

       CT2LST - Convert Local Civil Time to Local Mean Sidereal Time

       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)

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

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