Main Parameters
The coordinate origin of WGS 84 is meant to be located at the Earth's center of mass; the error is believed to be less than 2 cm.
The WGS 84 meridian of zero longitude is the IERS Reference Meridian, 5.31 arc seconds or 102.5 metres (336.3 ft) east of the Greenwich meridian at the latitude of the Royal Observatory.
The WGS 84 datum surface is an oblate spheroid (ellipsoid) with major (transverse) radius a = 6378137 m at the equator and flattening f = 1/298.257223563. The polar semi-minor (conjugate) radius b then equals a times (1 - f), or 6356752.3142 m.
Presently WGS 84 uses the EGM96 (Earth Gravitational Model 1996) geoid, revised in 2004. This geoid defines the nominal sea level surface by means of a spherical harmonics series of degree 360 (which provides about 100 km horizontal resolution). The deviations of the EGM96 geoid from the WGS 84 reference ellipsoid range from about −105 m to about +85 m. EGM96 differs from the original WGS 84 geoid, referred to as EGM84.
Read more about this topic: World Geodetic System
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