GRS 80
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[edit] 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 either its semi-minor axis (polar radius) b, aspect ratio (b / a) or flattening f. For GRS80, these are:
- Defining geometrical constants
- Semi-major axis = Equatorial Radius = a = 6,378,137.00000 m;
- Semi-minor axis = Polar Radius = b = 6,356,752.31414 m;
- Aspect ratio = b / a = 0.996647189318775;
- Flattening = f = 0.003352810681225;
- Reciprocal of flattening = 1 / f = 298.2572220972;
- Derived geometrical constants
- Quadratic mean radius= 6,372,797.5559 m;
- Authalic mean radius= 6,371,007.1810 m;
- Radius of a sphere of the same volume = (a2b)1 / 3 = 6,371,000.7900 m;
- Linear eccentricity = (a2 − b2).5 = 521,854.0097 m;
- Polar radius of curvature = a2 / b = 6,399,593.6259 m;
- Meridian quadrant = 10,001,965.7293 m;
- 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).
