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    Re: Ecef
    From: Herbert Prinz
    Date: 2001 Jul 24, 4:32 PM

    Earth Centered Earth Fixed Cartesian coordinates.
    The origin is at the center of the earth. The positive z-axis goes through the
    N-pole. The positive x-axis goes through the equator and the Greenwich
    meridian. The y-axis completes the orthogonal system.
    Roughly speaking, ECEF coordinates are what you get when you use the formula
    given by  R. van Gent and multiply with the radius of the Earth in meters.
      x = R * cos(lat) * cos(long)
      y = R * cos(lat) * sin(long)
      z = R * sin(lat)
    Strictly speaking, you must account for the spheroidal shape of the earth.
    These coordinates are easier to use in computers because all trigonometry
    becomes algebra. Your GPS reciever uses them internally, astronomers need them
    for exact topocentric reductions, or surveyors, for instance when they have to
    transform maps from one datum into another.
    There goes:
    Herbert Prinz (from 1368950/-4603950/4182550 ECEF)
    Dan Allen wrote:
    > Just what are ECEF coordinates?  I've never heard of them.

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