Understanding the GNSS RTK Concept

GPS is the most popular word that almost everyone who owns a smartphone understands the basics of the system- that is the positioning concept. There are other related systems such as the Russian GLONASS, Chinese Beidou, the European Union's Galileo and other localized systems like the Japanese Quasi-Zenith and Indian IRNSS. All these navigation systems work on the same principle of resection to determine location. GNSS RTK rover is the device that applies the resection principle to determine the precise position of a point using corrections provided by a static base station that continuously track the GNSS satellites.

The base and rover architecture has existed for more extended periods, and the traditional bubble based systems are being replaced by the new systems that do not require verticality to determine position accurately.  The working principle is the same though; the methods use a roving receiver and a base station to determine location accurately. The base station is set at a known point and allowed to track satellites for some time before beginning the data collection process. This setup is done to enable the base to settle for better accuracy in positions.

The roving receiver connects to the base station which measures pseudo-ranges to the satellite and determines the shift then sends the correction to the roving receiver. During initialization of the measurements, the roving receiver must stand at the end of the known baseline. This process is done to establish parameters for correction of accuracy. Data collection can then commence after initialization is over, but efficiency decreases with distance. GNSS RTK Network  solves the problem of reducing accuracy with distance by distributing references within acceptable ranges.

The GNSS RTK Network architecture implements a polygon-like architecture where references are placed at the corners of the study area so that the roving receiver can be moved around the regions to collect new points. Unlike the conventional RTK systems where the receiver connects to the base, these systems include an additional device that links the base stations to an online correction software. The online software performs necessary computations and sends parameters of correction to the roving receiver through an internet connection.

Several GNSS RTK Network systems exist, and they include the Virtual Reference Station (VRS), Master Auxiliary Corrections (MAX) and the Flachen Korrektur Parameter (FKP). All these systems operate on different principles all of which aim to achieve corrected positions of points when using a GNSS RTK Network. These systems simulate the standard RTK technique of determining the shift between the actual coordinates and the measured coordinates then sends the corrections to the roving receiver. This method results in the measurement of very accurate coordinates.

GNSS adoption increases annually due to their wide range of applications, and over time, drastic changes in the design of measurement instruments occur. The advancement in technology brings forth better results through improvement of positional accuracy up to a few millimeters which are acceptable for most engineering works. RTK system is one of the most advanced instruments that exist today for position determination, and the Leica GS18 T RTK is currently the best positioning instrument.