ECEF stands for Earth-Centered, Earth-Fixed, and is a Cartesian coordinate system used for GPS, and is sometimes known as a "conventional terrestrial" system^[1]. 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 a WGS84 Datum to ECEF can be used as an intermediate step in converting velocities to the North East Down coordinate system. Cartesian means relating to the French mathematician and philosopher Descartes, who, among other things, worked to merge algebra and Euclidean geometry. ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ... WGS 84 is the 1984 revision of the World Geodetic System. ...

External links

• ECEF datum transformation Notes on converting ECEF coordinates to WGS-84 datum

• Datum Transformations of GPS Positions Application Note More clear notes on converting ECEF coordinates to WGS-84 datum

• Geodetic Datum Overview Orientation of the coordinate system and additional information