WGS84 ellipsoid
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| WGS84 ellipsoid | |
|---|---|
| Name | WGS84 ellipsoid |
| Type | reference ellipsoid |
| Major axis | 6378137.0 m |
| Flattening | 1/298.257223563 |
| Datum | World Geodetic System 1984 |
WGS84 ellipsoid The WGS84 ellipsoid is the reference ellipsoid adopted for the World Geodetic System 1984 datum, serving as the mathematical surface used by Navstar GPS satellite positioning, National Geospatial-Intelligence Agency mapping, and international geodetic standards. It underpins coordinate frames used by agencies such as the United States Department of Defense, the International Hydrographic Organization, and the United Nations for global navigation, charting, and surveying. The ellipsoid parameters inform transformations between spatial reference systems used by organizations like the European Space Agency and the Japan Aerospace Exploration Agency.
Overview
The WGS84 ellipsoid provides a best-fit oblate spheroid approximating mean sea level for the Earth and is central to the World Geodetic System suite; it is referenced in operational systems including Global Positioning System receivers, geodetic networks maintained by the National Geodetic Survey, and mapping products from the Ordnance Survey. Major international programs such as Landsat, Sentinel satellite constellation, and the International GNSS Service rely on WGS84-compatible coordinates for data interoperability. Scientific initiatives including the Gravity Recovery and Climate Experiment and the International Terrestrial Reference Frame interface with WGS84 parameters for Earth science, oceanography, and climate research.
Definition and parameters
The ellipsoid is defined by a semi-major axis (equatorial radius) a = 6,378,137.0 m and an inverse flattening 1/f = 298.257223563, giving a semi-minor axis (polar radius) b and eccentricity e used in geodetic formulae applied by the Bureau of Land Management, the United States Geological Survey, and the Federal Aviation Administration. These parameters appear in transformation algorithms used by software libraries such as PROJ, GeographicLib, and the Geospatial Data Abstraction Library. Computational routines in packages like MATLAB, Python with NumPy, and R (programming language) implement the ellipsoid constants for map projections including Universal Transverse Mercator and Mercator projection conversions used by the United Nations Cartographic Section.
Relationship to WGS84 datum and coordinate systems
The WGS84 ellipsoid is the geometric surface for the WGS84 datum, which includes a realization of the ellipsoid’s center and orientation tied to the mass center of the Earth–Moon system and the International Celestial Reference Frame. This realization links WGS84 to the International Terrestrial Reference Frame used by agencies like the International Association of Geodesy and the European Centre for Medium-Range Weather Forecasts for global geolocation, timekeeping, and satellite orbit determination. Geographic coordinates (latitude, longitude, ellipsoidal height) in systems such as EPSG:4326 and services hosted by National Aeronautics and Space Administration mission control are routinely expressed relative to the WGS84 ellipsoid, while national datums like the North American Datum of 1983 and the European Terrestrial Reference System 1989 provide transformations to and from WGS84.
History and development
WGS84 evolved from earlier reference systems including the World Geodetic System 1972 and efforts by the Department of Defense to unify mapping for the Cold War era; contributors included personnel from the U.S. Army Corps of Engineers, the Defense Mapping Agency, and scientists associated with the Jet Propulsion Laboratory. Successive updates to the realization of WGS84 incorporated satellite tracking data from programs such as Transit (satellite) and TOPEX/Poseidon, and later refined by data from GPS networks and laser ranging to the LAGEOS satellites. International coordination with bodies like the International Union of Geodesy and Geophysics and the International Astronomical Union guided the adoption of parameters and alignments that reflect improved models of Earth rotation and gravity.
Usage and applications
The ellipsoid is used extensively by commercial navigation systems produced by companies such as Garmin, TomTom, and Apple Inc. for turn-by-turn navigation, by aviation navigation systems certified by the International Civil Aviation Organization, and in marine charting by the International Maritime Organization. Geospatial professionals at institutions like the World Bank and the Food and Agriculture Organization employ WGS84 in project mapping, while humanitarian operations coordinated by United Nations Office for the Coordination of Humanitarian Affairs use WGS84-based coordinates for logistics and disaster response. Scientific disciplines including seismology at the United States Geological Survey and oceanography at Scripps Institution of Oceanography utilize the ellipsoid for station positioning, tide modeling, and satellite altimetry referenced to WGS84.
Accuracy, limitations, and updates
While WGS84 provides a global, consistent reference suitable for most navigation and mapping, its ellipsoid is an approximation that does not account for regional geoid undulations measured by missions like GOCE and networks such as the Global Geodetic Observing System. Tectonic plate motion tracked by the Plate Tectonics research community causes time-dependent differences between static realizations, prompting realizations of WGS84 such as G1150 that align with the International Terrestrial Reference Frame epoch corrections used by the International GNSS Service. National mapping agencies including the Ordnance Survey and the National Geospatial-Intelligence Agency publish transformation grids and guidance to mitigate height and horizontal discrepancies between local datums and WGS84 for high-precision surveying and cadastral applications.