Other GNSS techniques

Virtual RINEX as a reference station for post-processing

Virtual RINEX is data for an "artificial" reference station based on data from real CORS. By specifying an approximate position and time, a RINEX file can be created using data from surrounding CORS. Virtual RINEX is created using the same software that is used in network RTK.

Post-processing of RTK measurements

As the name suggests, RTK (Real-Time Kinematic) is primarily intended as a real-time method, but this does not prevent you from applying the same principle to post-processing. When calculating RTK post-processing, you use virtual RINEX as reference data.

Virtual RINEX works in the same way as a so-called virtual reference station in real time, i.e., provides the necessary correction data – to reduce the effect of the ionosphere, among other things – to be able to make accurate positioning of your rover. You then need to collect raw data over a slightly longer period around the measurement in the field and make regular detailed measurements at the points that will later be post processed. With the help of virtual RINEX, you can then recalculate your RTK measurements in your own software with the possibility of equivalent quality as with RTK measurement in the field. For example, post-processed RTK can be very useful in areas with poor mobile coverage where corrections cannot be obtained in real time.

Post-processing of static measurement

You can also use virtual RINEX as reference data for post-processing of statically measured GNSS data. Virtual RINEX can be ordered for strategic locations around the network and then functions in the same way as reference data from a known control point, i.e., as a reference point for making a connection to the reference system in a network adjustment of static GNSS data.

Precise Point Positioning

Precise Point Positioning, PPP, is a kind of absolute positioning, originally developed by NASA's Jet Propulsion Laboratory. You can use PPP for both real-time and post-processing applications. The concept is based on observations from a GNSS receiver in combination with external information on the correction of satellite orbits and clock errors, as well as possible global or regional modelling of atmospheric error sources. This means that the user does not have a direct need for nearby CORS during the surveying, but a certain global or regional network of reference stations is required to model the sources of error.

In real-time applications, the method requires you to have a communication link to obtain the external correction information. The development of so-called PPP-RTK technology is underway to enable globally or regionally available positioning services in the long term, with the goal of achieving the same precision as today's network RTK services. A major challenge is to integrate new data and algorithms to reduce the currently long initialization times for PPP measurement.

PPP measurement provides coordinates in the current epoch in the latest ITRF solution. A transformation relationship is required to get coordinates in for example SWEREF 99. In the future, PPP-RTK may become an important alternative or complement to network RTK, not least in areas that lack geodetic infrastructure.