Geodetical Datum
Geodetical Datum :
The definition of a certain figure as best approximation on the real earth figure. It is represented by a set of parameters defining parts or the whole of the earth. For example the position coordinates of the position control points in the German Triangle Network relate to the datum called Rauenberg. In 19th century the position and orientation of the ellipsoid Bessel was clearly defined basing on astronomical localisation referring to the fundamental point near Berlin and on exact azimuth determination referring to the point Marienkirche. NAD 27 is the North-American Datum of 1927, ED 50 is the European Datum of 1950 and the WGS 84 means the World Geodatic System of 1984. Varying parameters like x- and y-shifts are used to achieve a better local approximation of a rotational ellipsoid in comparison to the real form of the earth/the geoid
