Datum and Ellipsoid Editing
To add a custom datum or ellipsoid, make sure a user defined coordinate system library has already been defined. To Create and Edit a User Coordinate System
CAUTION: Caution when using User-Defined Ellipsoids and Datums
When a Geographic Coordinate System (GCS) with a user-defined Ellipsoid or Datum is used in a model, it will not be recognized by earlier versions of MicroStation or PowerPlatform products. Upon opening the model, a message will be displayed stating that no Geographic Coordinate System is attached. Any geographically reprojected or transformed reference attachment that uses the modified GCS, will not display. Those references will be displayed in red in the References dialog. Hovering your cursor over any of the fields except the File Name, will result in the following tool tip: “Unable to perform required Geocoordinate Transformations”.