A map datum is a reference from which measurements are made. In geodesy, a geodetic or map datum is a set of reference points on the earth's surface against which position measurements are made, and (often) an associated model of the shape of the earth (reference ellipsoid) to define a geographic coordinate system. Some examples of geodetic datums are: NAD27, NAD83, ED50 etc...
An map datum can be defined in the Eye4Software Coordinate Calculator or Eye4Software GPS Toolkit using 7 parameters, also called Helmert-7 parameters:
Also an ellipsoid has to be specified when a map datum is defined.
|Map Datum Name||Unknown datum based upon the Average Terrestrial System 1977 ellipsoid|
|Ellipsoid Name||Average Terrestrial System 1977|
|Semi Major Axis||6378135|