A Validation of Localisation Accuracy Improvements by the Combined Use of GPS and GLONASS
For autonomous navigation in outdoor environments, robust and reliable positioning is an indispensable prerequisite. Looking at unstructured or a priori unknown surroundings the use of global navigation satellite systems (GNSS) is a reasonable approach . The Global Positioning System (GPS) is definitely the most popular GNSS. There are several efforts to build competing GNSS, from which only the Russian GLONASS is nearly operational. Nowadays, even recreation-grade GPS receivers often achieve an accuracy of less than 10m. But, since this is still not enough for many localisation and navigation tasks, several techniques have been developed to improve the positioning accuracy. In principle, all these methods use differential data coming from a base station at a well-known position. The GPS receiver applies the differential information in order to eliminate error sources like signal delays or inaccurate satellite orbits. Depending on the used method, this is called Code Differential GPS (DGPS) or Real Time Kinematics (RTK). Using sufficiently sophisticated receivers, with DGPS accuracy in the metre range can be reached. For RTK systems centimetre or even millimetre ranges are achievable.
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