In a method of conveying information regarding an orbit used at a Global Navigation Satellite System (GNSS) base station to a GNSS receiver, a satellite position is determined for a particular time from an orbit of a GNSS satellite. An ambiguity value is extracted from the satellite position. The ambiguity value is extracted based upon a satellite position determination margin of error of a GNSS receiver. The ambiguity value is encoded into an encoded ambiguity value which is assembled into a message. The message also includes a time tag representing the particular time. The message is transmitted from the GNSS base station. The encoded ambiguity value and the time tag convey information regarding the orbit to a GNSS receiver in receipt of the message.