- ECEF
**ECEF**stands for Earth-Centered, Earth-Fixed, and is aCartesian coordinate system used forGPS , and is sometimes known as a "conventional terrestrial" system [*Alfred Leick, 2004, "GPS Satellite Surveying", Wiley*] . It represents positions as an X, Y, and Z coordinate. The point (0,0,0) denotes the mass center of the earth, hence the name Earth-Centered. The z-axis is defined as being parallel to the earth rotational axes, pointing towards north. The x-axis intersects the sphere of the earth at the 0° latitude, 0° longitude. This means the ECEF rotates with the earth around its z-axis. Therefore, coordinates of a point fixed on the surface of the earth do not change, hence the name earth-fixed. Conversion from aWGS84 Datum to ECEF can be used as an intermediate step in converting velocities to theNorth East Down coordinate system.**References****External links*** [

*http://www.satsleuth.com/GPS_ECEF_Datum_transformation.htm ECEF datum transformation*] Notes on converting ECEF coordinates to WGS-84 datum

* [*http://www.microem.ru/pages/u_blox/tech/dataconvert/GPS.G1-X-00006.pdf Datum Transformations of GPS Positions Application Note*] More clear notes on converting ECEF coordinates to WGS-84 datum

* [*http://www.colorado.edu/geography/gcraft/notes/datum/datum.html Geodetic Datum Overview*] Orientation of the coordinate system and additional information

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**ECEF**— Electronic Commerce Executive Forum … Acronyms**ECEF**— Electronic Commerce Executive Forum … Acronyms von A bis Z**ECEF**— Earth Centered, Earth Fixed Contributor: MSFC … NASA Acronyms**Geodetic system**— For other uses, see Geodetic. Geodesy Fundamentals … Wikipedia**Earth Centered Inertial**— The Earth Centered Inertial (ECI) Frame is a non rotating version of the (ECEF) frame. The ECI frame is identical to the ECEF frame at some instant in time. The ECI frame is a convenient inertial frame for which Newton s second law is valid, and… … Wikipedia**Geodesy**— (pronEng|dʒiːˈɒdɪsi [OED] ), also called geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three dimensional time varying… … Wikipedia**Reference ellipsoid**— In geodesy, a reference ellipsoid is a mathematically defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body.Because of their relative simplicity, reference ellipsoids are used as a preferred surface… … Wikipedia**Orthographic projection (cartography)**— Orthographic projection (equatorial aspect) of eastern hemisphere 30W–150E An orthographic projection is a map projection of cartography. Like the stereographic projection and gnomonic projection, orthographic projection is a perspective (or… … Wikipedia**European Terrestrial Reference System 1989**— The European Terrestrial Reference System 1989 (ETRS89) is a ECEF (Earth Centered, Earth Fixed) geodetic Cartesian reference frame, in which the Eurasian Plate as a whole is static. The coordinates and maps in Europe based on ETRS89 are not… … Wikipedia**Polar motion**— is the movement of Earth s rotation axis across its surface. This is measured with respect to a reference frame in which the solid Earth is fixed (a so called Earth centered, Earth fixed or ECEF reference frame). This variation is only a few… … Wikipedia