ED50
ED 50 (European Datum 1950) is a geodetic datum which was defined after the 2nd World War for the international connection of geodetic networks.
It was based on the international Ellipsoid of 1909 resp. 1924 ("Hayford"-Ellipsoid) ( radius of the Earth's equator 6378,388 km, flattening 1:297) and widely used all over the world up to the eighties, when GRS80 and WGS84 was established.
Many national coordinate systems of Gauss-Krüger are defined by ED50 and oriented by means of Geodetic Astronomy. The data base of Up to now it is used in data bases of gravity field, cadastre, small surveying networks in Europe and America, and by some developing countries with no modern baselines.
The geodetic datum of ED50 is centered at the Frauenkirche of Munich in Southern Germany, where the approximalely center of the Western Europe national networks was situated in the years of the cold war. ED50 was also part of the fundamentals of the NATO coordinates (Gauss Krüger and UTM) up to the Eighties.