A key factor in the inventory of the road network condition is to be able to geographically position the measurement data at the right place with sufficient accuracy. By 31 March 2012, the correction service (EPOS), used to provide an improved positioning, will shut down. It is a paid service provided by Terracom. Because of low profitability it is now shutting down. With this, the Swedish Transport Administration would like to know if the free correction service EGNOS (European Geostationary Navigation Overlay Service) operated by ESA (European Space Agency) is possible to use instead. The test uses position data in the form of coordinates, collected on 18 routes throughout Sweden. The routes have different lengths from about 20 km to 105 km and road categories of various types, from secondary and tertiary roads to highways. Road infrastructure and environment is of different nature from the open coastal landscape to dense forest and from flat to hilly terrain. Three GPS receivers are used, one was a new receiver OxTS RT3050 with correction service EGNOS and was also equipped with an auxiliary system (inertial navigation system), and the two other receivers were both Trimble AgGP332, one using EGNOS, and the other acting as a reference, using the present system, EPOS (real-time correction of the GPS positions via FM band). The correction service EGNOS consists of three geostationary satellites over Europe and covers the whole of Sweden but with a poorer coverage and accuracy in northern Sweden. However, this was nothing that could be seen from the tests. The essential question that this study would provide answers to was if EGNOS can replace EPOS, which the tests show that it can. We have not been able to observe any systematic differences in position data. It appeared, however, that the reception quality of the two GPS receivers with the EGNOS correction services varied quite a bit and that the new and more modern receiver had a certain advantage in this respect. (Author/publisher) This report may be accessed by Internet users at http://www.vti.se/en/publications/pdf/test-of-correction-for-gps-receiv…
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