Definition
GRS 80, or Geodetic Reference System 1980, is a geodetic reference system consisting of a global reference ellipsoid and a gravity field model.
The reference elllipsoid is defined by its semi-major axis (equatorial
radius) <math>a<math> and flattening <math>f<math>. For GRS80, these are:
- Defining geometrical constants
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- Semi-major axis = Equatorial Radius = <math>a =<math>6,378,137.0 m,
- Reciprocal of flattening <math>1/f =<math> 298.257222101.
- Derived geometrical constants
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- Semi-minor axis = Polar Radius = 6,356,752.3141 m
- mean radius = <math>(2a + b) / 3<math> = 6,371,008.7714 m
- radius of a sphere with the same surface = 6,371,007.1810 m
- radius of a sphere of the same volume = 6,371,000.7900 m
- linear eccentricity = 521,854.0097 m
- Polar Radius of Curvature = 6,399,593.6259 m
- meridian quadrant = 10,001,965.7293 m
- flattening = 0.00335281068118
- Defining physical constants
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- Geocentric gravitational constant, including mass of the atmosphere <math>GM=<math> 3986005·108 m3/s2
- Dynamical form factor <math>J_2<math> = 108263· 10-8
- Angular velocity of rotation <math>\omega<math> = 7292115·10-11 s-1
For a complete definition, four independent constants are required. GRS80 chooses as these <math>a, GM, J_2<math> and <math>\omega<math>, making the geometical constant <math>f<math> a derived quantity.
Additional derived physical constants and geodetic formulas are found in the following reference: Geodetic Reference System 1980, Bulletin Géodésique, Vol 54:3, 1980.
The GRS80 reference system is used by the Global Positioning System, in a realization called WGS 84 (World Geodetic System 1984).
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