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ECI2GEO

ECI2GEO

Name


    ECI2GEO

Purpose


    Convert Earth-centered inertial coordinates to geographic spherical coords

Explanation


    Converts from ECI (Earth-Centered Inertial) (X,Y,Z) rectangular
    coordinates to geographic spherical coordinates (latitude, longitude,
    altitude). JD time is also needed as input.
    ECI coordinates are in km from Earth center at the supplied time (True of
    Date). Geographic coordinates are in degrees/degrees/km
    Geographic coordinates assume the Earth is a perfect sphere, with radius
    equal to its equatorial radius.

Calling Sequence


    gcoord=eci2geo(ECI_XYZ,JDtime)

Input


      ECI_XYZ : the ECI [X,Y,Z] coordinates (in km), can be an array [3,n]
                of n such coordinates. These should be at the supplied
                Julian Date (TOD - true of date).
      JDtime: the Julian Day time, double precision. Can be a 1-D array of n
                such times.

Keyword Inputs


      None

Output


      a 3-element array of geographic [latitude,longitude,altitude], or an
        array [3,n] of n such coordinates, double precision

Common Blocks


      None

Procedures Used


      CT2LST - Convert Local Civil Time to Local Mean Sidereal Time

Example


      IDL> gcoord=eci2geo([6378.137+600,0,0], 2452343.38982663D)
      IDL> print,gcoord
      0.0000000 232.27096 600.00000
      (The above is the geographic direction of the vernal point on
      2002/03/09 21:21:21.021, in geographic coordinates. The chosen
      altitude was 600 km.)
      gcoord can be further transformed into geodetic coordinates (using
      geo2geodetic.pro) or into geomagnetic coordinates (using geo2mag.pro)

Modification History


      Written by Pascal Saint-Hilaire (Saint-Hilaire@astro.phys.ethz.ch) on
              2001/05/13
      Modified on 2002/05/13, PSH : vectorization + use of JD times
      Document use of TOD epoch R. Redmon April 2014 NOAA/NGDC



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