Uniqueness

The central feature of Geodetics Epoch-by-Epoch™ GPS positioning technologies is that a high accuracy positioning solution, based on instantaneous integer ambiguity resolution, is achieved for each measurement epoch using only the observations collected at that epoch. Accordingly, each solution is independent of the solutions obtained for the previous and following epochs.

Successful resolution of integer-cycle phase ambiguities is a prerequisite for achieving the most precise position estimates with GPS by transforming precise but ambiguous phase measurements into precise unambiguous range measurements.

Other techniques such as real time kinematic (RTK) and rapid static surveying require multiple epochs of data in order to resolve phase ambiguities. RTK typically requires 30-45 s for resolving (initializing) integer-cycle phase ambiguities and reinitialization in the event that a receiver experiences loss of lock or cycle slips during the survey.

This is a severe limitation when trying to position a moving object such as a roving vehicle or maneuvering aircraft. Epoch-by-Epoch™ positioning only requires a single epoch for initialization and reinitialization making it extremely suitable for land, airborne and marine environments.

While traditional approaches such as RTK were designed to position a  single mobile receiver (rover) against a single base station, Geodetics' Precise Instantaneous GPS (piGPS) and Precise Instantaneous Network (PIN) positioning, based on Epoch-by-Epoch™ technology allows a mobile receiver to be positioned against a network of reference stations.  Further, the network processing can be performed at a central site, or at the rover.

The figure below illustrates the advantage of  Epoch-by-Epoch™ positioning in a simple example. 

Shown are the horizontal Epoch-by-Epoch™ positioning solutions for one moving receiver relative to one static receiver, which was 40-km away. Solutions were computed every second over about a 1.5 hr. time period (raw data-no filtering).

The moving receiver is located atop a model train. An obstacle was located above the train track to obstruct the satellite signals and cause loss of lock (the obstructed area is clearly seen in the lower portion of the train trajectory).

Current GPS RTK systems are unable to compute solutions for this example because they require a reinitialization period of about 30-45 seconds each time the obstacle obstructs the satellite signals.  This amounts to almost half of a single revolution of the train around the track.

Geodetics' Epoch-by-Epoch™ approach is unaffected by losses of lock so that the train's trajectory is clearly evident.