Ratan K. Awasthi
A continuously operating, GPS reference station – or permanent reference station as it is often called – comprise a GPS receiver and antenna set up in a stable manner at a safe location with a reliable power supply. The receiver operates continuously, logging raw data, perhaps also streaming (continuously outputting) raw data, and often outputting Real Time Kinematic (RTK) and Differential GPS (DGPS) data for transmission to RTK, GIS and GPS navigation devices. The receiver is usually controlled by a computer that can be located remotely if necessary. The PC will usually download data files at regular intervals and pass them to an FTP server for access by the GPS user community.
One or more single reference stations supply GPS Services to users in the immediate surrounding areas may be all that is required by some organizations. Other authorities, however, may need to establish networks of reference stations – perhaps 5,10,20,50, or even more stations – to provide complete GPS services over entire regions and even countries. A single server (computer) running a GPS reference station software and communicating by telephone, LAN, WAN or Internet can control all the stations in the network (PC’s are not required at the receivers).
This brief introduction illustrates that reference stations and networks can vary considerably in extent and complexity. Organizations that are studying the establishment of reference stations should consider carefully what the stations will be used for, what services they will have to provide, and what will be the appropriate levels of sophistication and cost.
Once set up and configured, the stations and network will run fully automatically. However, system supervisors can log in, inspect the receivers and the network and make any changes that are necessary.
The main requirement today is to provide the data needed by real-time survey and GIS rover equipment. The receivers at the reference stations can output data in standard Radio Technical Commission for Maritime Services (RTCM) formats and in other proprietary formats (Leica, CMR, CMR+) for transmission to and use by RTK and GIS field rover receivers. Transmission can be directly from the stations or via other suitable locations. Communication for transmission of RTK and DGPS data will usually be by radio, high-speed wireless (GSM, GPRS, CDMA) etc.) or even by the Internet.
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