Other GNSS techniques

Virtual RINEX can be used as reference data for post-processing of both RTK data and static GNSS data. PPP is a method that is increasingly being developed for absolute positioning without the need for connection to nearby reference stations.

Virtual RINEX

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

Post-processing of RTK measurements

As the name suggests, RTK (Real-Time Kinematic) is mainly intended as a real-time method, but it does not prevent the same principle from being applied with post-processing instead. In post-processing of RTK, virtual RINEX is often used as reference data.

Virtual RINEX then functions 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, among other things, the ionosphere - to be able to accurately position the user's rover. The user then needs to collect raw data over a slightly longer period covering the measurement in the field and during that period make regular detail surveys at the points that are to be recalculated later. With the help of virtual RINEX, the user can then post-process the detail surveys in his own software with the possibility of achieveing equivalent quality as with real-time RTK measurements in the field. Post-processed RTK can, for example, be very useful in areas with poor mobile coverage.

Post-processing of static measurement

Virtual RINEX can also be used 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 a corresponding way as reference data from a known ground control, i.e. as a reference point for making a connection to the reference system for 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, for both real-time and post-processing applications. The concept is based on observations from a GNSS receiver combined with external information on the correction of satellite orbits and clock errors as well as possible global or regional modeling of atmospheric sources of error. This means that the user is not in direct need of nearby reference stations when measuring, 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 a communication link to obtain the external correction information. Development of so-called PPP-RTK technology is ongoing to enable globally or regionally available positioning services with 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 measurements.

PPP measurement gives coordinates in the latest ITRF solution, current epoch. To get coordinates in for example SWEREF 99, a transformation relationship between these systems is required. PPP-RTK may in the future be an important alternative or complement to network RTK, not least in areas without geodetic infrastructure.

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