Real Time Mapping with Dgps-enabled Navigation Equipment

Today, differential GPS techniques allow common GPS receivers to achieve the precision levels required for mapping purposes. The development of systems for mobile Internet access (mainly GPRS) provides a fast and reliable method for feeding differential corrections to a GPS receiver in any area covered by a cell telephone network. With the increase in the available bandwidth, and the example of data streaming applications like Internet-Radio or Internet-TV, the researchers are now trying to use the Internet as a medium for transmitting GNSS code and phase corrections for real-time surveys, and examining advantages and limitations of this approach. In this context the EUREF (EUropean REference Frame) started in June 2002 a project named EUREF-IP, with the purpose of developing a stable and robust infrastructure for broadcasting differential corrections via Internet. Inside this project the Topography Section of the University of Cagliari has settled up a permanent station, which since July 2002 sends differential corrections over the Internet for DGPS and RTK positioning. The permanent station, identified as “CAGZ”, is part of the IGLOS network and, since October 2003, of the EPN network. This paper describes the CAGZ permanent station, the servers software and the field tests performed during this two years of uninterrupted GNSS data transmission, to evaluate the performances of the two servers activated. Also different network connections (LAN, GSM-Internet, GPRS-Internet) were compared in order to assess the improvements achieved by transmission medium. We present also some DGPS ant RTK surveys, performed with geodetic and handheld receivers for updating medium-scale and large-scale cartography.