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Development of a Network Real-Time Kinematic Processing Platform

Single baseline “real-time kinematic” (RTK) GNSS positioning is a carrier-phase-based relative positioning technique that delivers centimetre-level accuracy in realtime. In general, this technique satisfies the GPS receiver manufacturers‟ accuracy specification (e.g. 5-10mm +/1ppm) for baseline lengths of up to approximately 20km due to the distance dependent errors. The Network-RTK (NRTK) concept was introduced to overcome the limitation of the baseline distance while improving the positioning accuracy and repeatability. Rapid growth and development of information and communication technologies has enabled GPS service operators to broadcast the network correction via the Internet. In accordance with this trend, the development of a research-oriented real-time data processing platform for NRTK positioning was initiated by the School of Surveying and Spatial Information Systems at the University of New South Wales (UNSW), Sydney, Australia. This platform is being used to investigate different algorithms as well as issues such as network latency, data synchronisation, positioning quality, and others. This NRTK system is known as „SNAPper‟. SNAPper receives GPS data streams from Continuously Operating Reference Stations (CORS) and generates realtime network corrections using International GNSS Services (IGS) ultra-rapid orbits, and provides users with Virtual Reference Station (VRS) measurements. A robust ambiguity resolution algorithm was implemented for high precision positioning using corrections computed from a CORS network. In order to evaluate the performance of the SNAPper software, a range of numeral tests have been carried out. The Vicmap Position-GPSnetTM, operated by the Victorian Department of Sustainability and Environment, Melbourne, was chosen as a test network, however, actual data processing was conducted at UNSW to demonstrate the capability of remote processing. The test results show that the implemented RTK algorithm can deliver precise positioning with centimetre-level accuracy in real-time.