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    Re: Ecef
    From: Lu Abel
    Date: 2001 Jul 24, 8:35 PM

    1.  What are the units of measurement?  I think I could grasp
    1368950/-4603950/4182550 more easily with a unit of measurement.
    
    2.  I don't necessarily agree that it might make determination of our
    centroid easier. An average in ECEF coordinates would easily give us a
    point in the middle of the earth!   Don't know about you, but I prefer
    sailing to digging :-)
    
    Lu Abel
    
    At 10:31 PM 7/24/2001 +0000, you wrote:
    >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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