Joël van Cranenbroeck
Business Development Director for GNSS
Reference Stations and Structural Monitoring Solutions,
Leica Geosystems AG, Heerbrugg, Switzerland
Email: [email protected]
In light of a few limitations of existing approaches to network corrections, Leica Geosystems has driven the development and adoption of the Master-Auxiliary Concept within the RTCM Special Committee 104
Leica Geosystems has been for many years actively researching and promoting network Real Time Kinematic (RTK) solutions and working towards an industry standard for network RTK corrections. It is in this role that Leica Geosystems has developed and driven the Master-Auxiliary Concept (MAC), the future of networked RTK and the basis for the forthcoming RTCM 3.0 network correction message standard. The Master-Auxiliary corrections (MAX) are compact and efficient to transmit to the rover, but also robust and flexible. The Master-Auxiliary Concept overcomes all of the weaknesses of the previous approaches that have been used until now by giving the rover the capability to derive the maximum benefit from the information provided by a reference station network even over a broadcast/one-way communication medium. In conjunction with this new standard, Leica Geosystems announced the Leica GPS Spider 2.0 software with its new network RTK module SpiderNet, which draws on the latest zero-difference processing techniques to take the Master-Auxiliary Concept to the maximum reliability, maximum performance, maximum flexibility and maximum security.
THE BASICS OF NETWORK RTK
The motivation behind using multiple reference stations in a network for GPS corrections is to model and correct for distance-dependent errors that reduce the accuracy of conventional RTK or DGPS positions in proportion to the distance from a rover to its nearest reference station. It is well known that the most significant sources of error affecting precise GPS positioning are the ionosphere, troposphere and satellite orbits. The influence of the ionospheric error on different frequencies in the L-band used by satellite navigation systems is well understood. The ionosphere, which is subject to rapid and localised disturbances, is the main restriction on the station density in a reference network. The troposphere and orbit errors have an equal effect on all ranging signals used by current satellite-based global navigation systems. The aim of a reference network is to model and estimate these error sources and provide this network correction information to rover users so that they may derive positions with a higher accuracy than with conventional RTK. Until the release of RTCM 3.0, there has been no official internationally accepted standard for network RTK corrections. Prior to the release of RTCM 3.0, two approaches, namely those making use of area correction parameters FKP and ‘virtual’ reference stations VRS, were adopted by the user community as interim measures, both of which have serious flaws in their concept and methodology.
In light of these and other limitations of existing approaches to network corrections, Leica Geosystems has driven the development and adoption of the Master-Auxiliary Concept within the RTCM Special Committee 104.
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