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The World Geodetic System (WGS) is a standard for use in cartography, geodesy, and navigation including by GPS. It comprises a standard coordinate system for the Earth, a standard spheroidal reference surface (the ''datum'' or ''reference ellipsoid'') for raw altitude data, and a gravitational equipotential surface (the ''geoid'') that defines the ''nominal sea level''. The latest revision is WGS 84 (aka WGS 1984, EPSG:4326), established in 1984 and last revised in 2004. Earlier schemes included WGS 72, WGS 66, and WGS 60. WGS 84 is the reference coordinate system used by the Global Positioning System. ==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,〔European Organisation for the Safety of Air Navigation and IfEN: WGS 84 Implementation Manual, p. 13. 1998〕 5.31 arc seconds or east of the Greenwich meridian at the latitude of the Royal Observatory.〔(History of the Prime Meridian -Past and Present )〕〔National Maritime Museum: "(The Longitude of Greenwich )"〕 The WGS 84 datum surface is an oblate spheroid (ellipsoid) with major (equatorial) radius ''a'' = m at the equator and flattening ''f'' = 1/.〔National Imagery and Mapping Agency Technical Report TR 8350.2 Third Edition, Amendment 1, 1 Jan 2000, "Department of Defense World Geodetic System 1984"〕 The polar semi-minor axis ''b'' then equals ''a'' times (1−''f''), or m.〔 Currently, 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 latitudinal resolution near the Equator).〔(NGA/NASA EGM96, N=M=360 Earth Gravitational Model )〕 The deviations of the EGM96 geoid from the WGS 84 reference ellipsoid range from about −105 m to about +85 m.〔(EGM96 15' × 15' Geoid Undulation Plot )〕 EGM96 differs from the original WGS 84 geoid, referred to as EGM84. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「World Geodetic System」の詳細全文を読む スポンサード リンク
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