Development of a Network Real-Time Kinematic Processing Platform Heo, Y., Li, B., Lim, S., Rizos, C., The School of Surveying and Spatial Information Systems, UNSW, Australia BIOGRAPHIES Yong Heo is a research assistant in the School of Surveying & Spatial Information Systems, the University of New South Wales (UNSW), Sydney, Australia. Yong received his B.Sc. from the School of Computer Science and Engineering, UNSW, in 2007. Binghao Li is a research associate in the School of Surveying & Spatial Information Systems, UNSW. Binghao obtained B.Sc. in Electrical & Mechanical Eng. from Northern Jiaotong University, P.R. China, in 1994, and M.Sc. in Civil Eng., Tsinghua University, P.R. China, in 2001. He received his Ph.D. from UNSW in 2006. His research area is pedestrian navigation and network-RTK algorithm development. Samsung Lim is a senior lecturer in the School of Surveying & Spatial Information Systems, UNSW. For the past fifteen years his research has focused on the areas of GNSS and GIS. Samsung's research interests are in theoretical problems related to RTK-GPS and applying geospatial information technologies to real-world problems. Samsung received his B.A. and M.A. in Mathematics from Seoul National University, South Korea, and his Ph.D. in Aerospace Engineering and Engineering Mechanics from the University of Texas at Austin, USA. Chris Rizos is currently Professor and Head of the School of Surveying & Spatial Information Systems, UNSW. Chris has been researching the technology and high precision applications of GPS since 1985, and has published over 350 journal and conference papers. He is a Fellow of the Australian Institute of Navigation and a Fellow of the International Association of Geodesy (IAG). He is currently the Vice President of the IAG and a member of the Governing Board of the International GNSS Service. ABSTRACT Single baseline “real-time kinematic” (RTK) GNSS positioning is a carrier-phase-based relative positioning technique that delivers centimetre-level accuracy in real- time. 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 real- time 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-GPSnet™, 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. 1. INTRODUCTION Real-Time Kinematic (RTK) positioning is a carrier- phase-based GNSS relative positioning technique for delivering centimetre-level accuracy in real-time. Since RTK was introduced in the early 1990s it has been widely used for high accuracy applications such as surveying, mapping and machine guidance. A relative positioning technique requires data communication links between a reference receiver and a rover receiver. Traditionally, radio frequency (RF) data communication channels such as MF, HF, VHF and UHF have been used to transmit the GPS corrections. However, such radio transmissions suffer from distance limitations because RF links become