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GRS 80
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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) a and flattening f. For GRS80, these are:
- Defining geometrical constants
- Semi-major axis = Equatorial Radius = a = 6,378,137.0 m,
- Reciprocal of flattening 1 / f = 298.257222101.
- Derived geometrical constants
- Semi-minor axis = Polar Radius = 6,356,752.3141 m
- mean radius = (2a + b) / 3 = 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
- Geocentric gravitational constant, including mass of the atmosphere GM = 3986005·108 m3/s2
- Dynamical form factor J2 = 108263· 10-8
- Angular velocity of rotation ω = 7292115·10-11 s-1
For a complete definition, four independent constants are required. GRS80 chooses as these a,GM,J2 and ω, making the geometical constant f 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).
Last updated: 03-18-2005 11:16:12