Datum definition in the gps era

The dramatic changes in geodetic practice brought about by the implementation of GPS may call for a change in our understanding and definition of the geodetic datum. The contribution of GPS measurements is divided into a “datum-definition” component and into a datumless “differential” component. In densification of geodetic control only the datumless component is to be employed. In the establishment of a primary geodetic network both components can be used. However, the datum-definition component serves mainly as a data source for determining the ever-changing relationship between the GPS datum and datum of the geodetic network.