To Edit a Datum

To Add or Edit a datum, right-click on the user defined library and select the appropriate option.
Fill in the various entries as required. Only the datums for which conversion to WGS84 can be specified using mathematical parameters can be created. Those types are available from the Conversion Method pull down list. The parameters to be defined will differ based on the conversion method selected.

Tip: Between three and seven parameters are required for each of the conversion types. Delta parameters are entered in meters, rotation parameters are entered in degrees, and the scale parameter is entered in parts per million.

A datum requires an ellipsoid. The available ellipsoids are those that are in the same user library and those that are in the system library. The user library ellipsoids will be at the top of the list.