Editing Geodetic Reference System 1980 (section)

==Definition==
The reference ellipsoid is usually defined by its [[semi-major axis]] (equatorial
radius) <math>a</math> and either its [[semi-minor axis]] (polar radius) <math>b</math>, [[aspect ratio]] <math>(b/a)</math> or [[flattening]] <math>f</math>, but GRS80 is an exception: ''four'' independent constants are required for a complete definition. GRS80 chooses as these <math>a</math>, <math>GM</math>, <math>J_2</math> and <math>\omega</math>, making the geometrical constant <math>f</math> a derived quantity.

; Defining [[geometrical]] [[constant (mathematics)|constants]]
:Semi-major axis = Equatorial Radius = <math>a = 6\,378\,137\,\mathrm{m}</math>;

; Defining [[nature|physical]] [[constant (mathematics)|constants]]
:[[Geocentric gravitational constant]] determined from the [[gravitational constant]] and the [[earth mass]] with atmosphere <math>GM = 3986005\times10^8\, \mathrm{m^3/s^2}</math>;
:Dynamical form factor <math>J_2 = 108\,263\times10^{-8}</math>;
:Angular velocity of rotation <math>\omega = 7\,292\,115\times10^{-11}\, \mathrm{s^{-1}}</math>;