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

Defining physical constants 

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).