Global navigation satellite system
GPS is the United States version of a Global Navigation Satellite System (GNSS). GPS is owned and operated by the United State's military. There are several similar systems. The Russians have GLONASS. The European Union offers Galileo. China has BeiDou. India offers NAVIC and Japan has the Quasi-Zenith system. GPS and GLONASS are fully deployed. The other systems are schooled to come on line over the next several years.
All of these systems work in a similar fashion. Multiple satellites transmit radio signals to earth. The receiver determines the distance to several satellites then uses these distances to triangulate its position. There can be errors attributable to elevation, the curvature of the earth, and atmospheric distortions. But, better antennas include error correction algorithms (Satellite Based Augmentation Systems). In the end, the accuracy of the system depends on the quality of this error correction and the number of satellites it is able to "see." We want a system with EGNOS, WAAS, and MSAS error correction systems. Further we want a system able to use GPS, GLONASS, and BeiDou. Such a system ought to be accurate to within about 15 feet. This level of precision may seem unnecessary. But, the greater the precision, the more accurately our Autopilot will be to learn the steering characteristics of the boat.
All of the major electronics manufacturers offer GPS antennas. In fact, most companies bundle GPS antennas with their chartplotters.
In the end, we chose to go with a third party manufacturer, Lars Thrane. The LT-1000 is represented as a reference quality antenna. This sensor provides true heading, roll, pitch, position, ground speed, course over ground, air pressure, and temperature. It is a 72 channel receiver able to receive signals from GPS, GLONASS and BeiDou. The sensor recognizes the leading satellite based error correction schemes. The LT-1000 broadcasts simultaneously in NMEA0183 and NMEA2000 meaning we can connect it to both our Navigation Computer and our Chartplotters.