The transmission of GNSS Data in the DISTART Network for Real Time Kinematic Positioning

The GNSS RTK-Networks have been aroused a great interest for the advantages in the surveying of the territory in comparison to the traditional RTK methodology. The DISTART in the last year has improved a Network for RTK positioning. At present the net is composed by 8 permanent stations. The control centre is nearby the Department of DISTART of Bologna University. This network is fundamental to investigate all aspects concerning the networks for real time applications. Particularly, not only the topographic feature is investigated, but a very important aspect concerning the data transmission infrastructure is analyzed. In fact the first experimentations demonstrated that the performance of the topographic network depends on the guarantee of a correct data transmission from the GNSS permanent stations to the Control Centre. To investigate on this field we built a network composed by mixed physical data transmission infrastructure between control centre and the permanent stations on the territory (topographic baselines about 70-80 Km) using university Italian network (GARR) and commercial networks. We studied the time of latency of data transmitted, that is an important aspect of the network, because to solve ambiguities every software for real time network solution needs that the GNSS permanent station observations arrives with a latency not too much greater than a second. Parallely we studied other important aspects of the data transmission in the network like the NAPs (Network Access Protocols), the velocities, the data formats (RTCM 2.X, RTCM 3.0). In this work we want to give the direction to characterize a procedure step by step of a network installation, with the purpose to define a standard, possibly certified, about procedures, materials, softwares to use to install a network of GNSS permanent stations for RTK positioning.