# Geodetic reference system 1980

The Geodetic Reference System 1980 ( GRS 80 , English Geodetic Reference System 1980 ) is an earth model that includes the most important parameters of the earth's shape , the earth's rotation and the gravitational field .

The reference ellipsoid of the GRS 80 serves the European spatial reference system ETRS89 as a geometrical calculation and mapping surface and with it forms the geodetic datum for uniform national surveying . The compliant UTM mapping is used as the mapping system. In Germany, the Gauss-Krüger coordinates related to the Bessel ellipsoid ( Potsdam date ) and the Krassowski ellipsoid ( Pulkovo date ) are converted to GRS80 and UTM.

GRS 80 also defines the normal gravity and thus replaces GRS 67 . WGS 84 practically uses the ellipsoid of the GRS 80 but contains more data about the gravitational field .

GRS 80 was adopted in 1979 at the general assembly of the IUGG , the international umbrella organization for geodesy and geophysics , and published in detail in 1980  by the head of the study group, Helmut Moritz , after consultation with the International Astronomical Union (IAU) .

The four defining geometric and physical parameters are:

 Major semi-axis / equator radius ${\ displaystyle a = 6 {,} 378 \, 137 \ cdot 10 ^ {6} \, {\ textrm {m}}}$ Gravitational constant times earth mass (more precisely measurable than the individual factors) ${\ displaystyle GM _ {\ oplus} = 3 {,} 986 \, 005 \ cdot 10 ^ {14} \, {\ textrm {m}} ^ {3} / {\ textrm {s}} ^ {2} \ ,}$ Difference in the main moments of inertia related to  M ⊕ a 2 (without the influence of tidal forces ) ${\ displaystyle J_ {2} = 1 {,} 08263 \ cdot 10 ^ {- 3}}$ Angular velocity (including information on the orientation of the axis of rotation and the prime meridian ) ${\ displaystyle \ omega = 7 {,} 292 \, 115 \ cdot 10 ^ {- 5} \, {\ textrm {rad / s}} \,}$

The derived parameters for describing the shape of the Earth's ellipsoid are:

 Small semi-axis / pole half-axis ${\ displaystyle b \ approx 6 {,} 356 \, 752 \, 314 \ cdot 10 ^ {6} \, {\ textrm {m}}}$ Parameters of Earth flattening ${\ displaystyle f ^ {- 1} \ approx 2 {,} 98257222 \ cdot 10 ^ {2}}$