Geodetic Reference System 

Geodetic Reference System of 1980 (GRS80) GRS80  [geodesy] Acronym for Geodetic Reference System of 1980. The standard measurements of the earth's shape and size adopted by the International Union of Geodesy and Geophysics in 1979. [Category=Geospatial ] ...
geodetic reference system the technical name for a datum. The combination of an ellipsoid, which specifies the size and shape of the earth, and a base point from which the latitude and longitude of all other points are referenced geodetic survey ...
Geodetic Reference System of 1980 GRSU Geography Remote Sensing Unit (Univ. of California, Santa Barbara) ...
The 1980 Geodetic Reference System (GRS80) posited a 6,378,137 m semimajor axis and a 1:298.257 flattening. This system was adopted at the XVII General Assembly of the International Union of Geodesy and Geophysics (IUGG).
National Geodetic Reference System (USA) NGS National Geographic Society (USA); National Geodetic Survey (U.S.) ...
GRS80 (Geodetic Reference System of 1980)  A standard defining the size and shape of the Earth as adopted by the International Union of Geodesy and Geophysics in 1979. ...
The GRS80 (Geodetic Reference System 1980) as approved and adopted by the IUGG at its Canberra, Australia meeting of 1979 is based on the equatorial radius (semimajor axis of Earth ellipsoid) a, total mass GM, dynamic form factor J2 and angular velocity of rotation ω, ...
At its general assembly 1979 in Canberra the IUGG recognized that the Geodetic Reference System 1967 no longer represents the size and shape of the earth to an adequate accuracy. Consequently, it was replaced by the Geodetic Reference System 1980 (GRS 1980 see table).
Both are geodetic reference systems, but each is based on different measurements. NAD 27 incorporated all horizontal geodetic surveys completed up to 1927. NAD 83 updated NAD 27 with current measurements using radio astronomy and satellite observations.
[geodesy] Acronym for Geodetic Reference System of 1980. The standard measurements of the earth's shape and size adopted by the International Union of Geodesy and Geophysics in 1979.
Horizontal Datum Name: North American Datum of 1983 Ellipsoid Name: Geodetic Reference System 80 Semimajor Axis: 6378206 Denominator of Flattening Ratio: 294.9786982 ...
In addition, geodata are frequently captured and stored in a different geographic projection, coordinate system, or geodetic reference system than needed for an application, especially where multiple map layers are involved.
To facilitate the use of satellite surveying and navigation systems, the new datum was redefined using the Geodetic Reference System 1980 (GRS 80) as the reference ellipsoid because this model more closely approximates the true size and shape of the Earth.
Military in 1984, are internationally accepted as the geodetic reference system (GRS 80). Geographic Coordinates simply refers to the system of latitude and longitude.
1927 uses the Clarke's ellipsoid, while 1983 uses the 1980 Geodetic Reference System. The plural of a geodetic datum is 'datums', despite the Latin origins. NPComplete p.
The most recently developed and widely used is the World Geodetic System of 1984 (WGS84). Another independent measurement commonly used is the Geodetic Reference System of 1980 (GRS80). These spheroids differ slightly but can be assumed to be identical for almost all mapping purposes.
See also: Geodetic, Coordinate, Survey, Accuracy, Model
