Custom GPS-Correction Server for Real-Time Trajectography

Centimeter-level real-time kinematic (RTK) positioning is one of the most widely used surveying techniques. Broadcasting GPS-RTK corrections via Internet-based services has become a new communication procedure to achieve “instantaneous” positioning with high accuracy. This procedure generally involves a Virtual Reference Station (VRS), the data of which are derived from a network of GPS stations continuously linked to a control center. Its public implementation implies GDGPS (NASA Global Differential GPS) or NTRIP (Networked Transport of RTCM via IP Protocol) to disseminate 1-Hz data streams to stationary users over the Internet. Like their proprietary counterparts implemented by world-class GPS manufacturers, GDGPS and NTRIP are designed as high-quality positioning services that provide their clients RTK corrections whose format and pace are strictly defined. This restricts their use to surveying tasks for pedestrians. GPS-based trajectography in real time is an emerging technique requiring high-cadency data streams that needs a novel approach. This paper describes an architecture that fully exploits the generous bandwidth of the wireless Internet, so that the RTK users may remotely invoke custom applications on the server side. The emphasis will be on designing a multi-client broadcaster of GPS corrections that registers the trajectory of all the connected rovers in real time. Practical experiments will assess the tracking quality of fast moving rovers.