The use of DGPS-RTK measurements through GSM network for GIS environments

The necessity to get positioning in the most precise way and in the briefest time assumes great importance either in the navigational field or in the geodetic surveys. The GPS system is really the most proper tool to meet such expectations. The purpose of DGPS is, essentially, to transform the absolute positioning of a point (fixed or mobile) in a relative positioning in comparison with another that can be considered fixed and of known coordinates in a determinate reference system. The paper describes some experiments in course at the Polytechnic of Bari on the transmission of D-GPS correction signals in local region by the use of a GSM mobile phone with the Bluetooth wireless connection to the GPS receiver. The rover GPS must be connected to permanent reference station of GPS national network (GeoTIM Network) through the GSM phone, provided of a normal telephone card for data transmission: the correction is directly effected during the survey (RTK) using the standard protocol RTCM. An advantage from the economic point of view, it’s the possibility to operate in real time for geodetic surveys only with one “low-cost” receiver, continuously connected to a permanent GPS-station. The results of this experimentation are very useful both to verify the real functionality of the TIM "GeoData" system, and to develope the use of a GPS receiver for GIS data collection with sub-meter accuracy.