UNA STAZIONE GPS SEMI-PERMANENTE PER IL POSIZIONAMENTO RTK IN REAL TIME

In the field of the GNSS (Global Navigation Satellite System) with the NavStar GPS and Glonass systems it is already known and common the RTK real time positioning method. The RTK involves two, or more, GNSS receivers, the first one called Master set up on a landmark, and the second one, or ones, called Rover/s, used for the land surveying of the unkown points. At the beginning, the data link for the transmission of the differential correction from the Master to the Rover/s was made by radio links. Then, twice GSM modems have been used for the radio link, thanks to the spread of the GMS services, above all in the European countries. Then, an increasingly number of permanent GNSS – GPS stations has been installed. Many of them are connected to elaboration centres. These centres elaborate the differential correction, in real time, and make available them for the GPS-rover-users, often after an elaboration based on specific algorithms (such as VRS, FKP, MAC and so on). With an handheld palmtop device furnished with a modem for mobile connections, the users can take the differential corrections made by elaboration centres and send them to their Rover GNSS receivers. In the present PhD thesis, two different solutions are presented, the first one alternative to the second one. The first one is a software called ClientNTRIP, designed and compiled for handheld devices with the Windows Mobile 5 and Windows Mobile 6 operative system. This software - based on the NTRIP RTCM standard - allows the connection to the data centres, taking the differential corrections and sending them to the GNSS rover receivers. It is also able to collect the NMEA messages from the same communication port of the GNSS receivers and, after some elaborations, records them into files. The second solution proposed in this PhD thesis is called SemPeMuBas (SemiPermanent Multi Base Station). The approach for the RTK real time positioning followed with the SemPeMuBas is completely different from the first solution presented. With the second solution, in fact, two GNSS receivers, Master and Rover, are already necessary. However, the data connection from the Master to the Rover is made by a mobile internet connection, based on the GPRS, EDGE or UTMS services, instead of GSM data link. This system requires two palmtop computers with GPRS – EDGE – UMTS modems. The first one is set up near the Master GNSS receiver, and a software called Server is installed on it. The second one is set up near the Rover GNSS receiver, and a Client software is installed on it. The main benefits of the SemPeMuBaS towards a GSM data link are: • Possibility of connection from one Master to one or more Rover, at the same time. • The costs of Internet Mobile Connection are widely less towards the costs of GSM data calls. From the main benefits of the SemPeMuBaS towards the use of GPS – GNSS permanent stations, we should make mention of: • Complete control of the operator over the Master and Rover stations, independently of differential correction services furnished by third. • Fee and fixed costs absence; absence of the need of registration; absence of troubles made by the privacy, caused during the use of third part services, by the delivery of the positions occupied during the surveying to the elaboration data centres. • Use of the datum, of the differential correction protocol and of their frequency, fixed by the GPS-Rover user. The chapters are organized in this way: • Chapter 1 : The differential correction messages. In this chapter, the most common differential correction formats are described: RTCM 2.X, RTCM 3.X and CMR. • Chapter 2 : Development of a NTRIP-TCP Client for Windows Mobile 5. The NTRIP Client for Windows Mobile 5 is described. The software is able to connect to the elaboration date centres ( called Casters) using the RTCM NTRIP protocol. Some laboratory test is presented. • Chapter 3: The SemPeMuBaS (Semi Permanent Multi Base Station). A first prototype of the Semi Permanent Multi Base Station is showed and described. It was based for the Windows Pocket PC 2002 operative system. • Chapter 4: The operative stage of the Semi Permanent Multi Base Station. This chapter describes the last version of the SemPeMuBaS, compiled in the National Instruments Lab View 8.5.1 environment. This version works on Windows Mobile 5 and 6 operative systems. It is composed by two softwares: the Server and the Client. Some laboratory tests are presented. • Chapter 5: External tests. In this chapter, some external texts are described, made with one rover only and then some other with two rovers connected at the same time to the same Server-Master. In conclusion, the two different solution, the NTRIP Client and the SemPerMuBas (SemiPermanent Multi Base Station made by two softwares: Server and Client), are perfectly working on the palmtop computer devices with the Windows Mobile 5 and Windows Mobile 6 operating systems. The land surveyors will be able to appreciate their benefits during the RTK real TIME GPS positioning.