The Global Positioning System (GPS) is one of several networks of Worldwide Navigation Satellite Systems (GNSS). GPS consists of a network of 32 satellites on six elliptical (almost circular) orbits at an altitude of about 20.200 km.
Each satellite broadcasts a military (P coded - encrypted) and civilian (C coded - unencrypted) signal.
A GPS tracker receives the time stamp and calculates location, speed and direction. Today's orbits are designed to ensure that receivers will be visible to at least nine satellites at all times.
Since the year 2000 GPS (officially NAVSTAR GPS) is also available for civil purposes with sufficient accuracy. Besides the US-American version, some GPS devices also use the Russian GLONASS. The European (non-military) Galileo still plays hardly any role in practical use. Thanks to GPS, the exact location can be determined at any time and at almost any place, and this positioning forms the basis for all other functions (such as map display and routing).
How does GPS work?
About 30 GPS satellites orbit the earth and send signals.
The GPS receiver compares the time at which the signal was sent with the time at which the signal was received. From the time difference and the satellite position, the distance of the GPS device from the satellite is calculated. If you have the signals from 3 satellites, you can determine the position with the so-called trilateration. Up to an accuracy of 5 m the reception is only accurate from 4 satellites, then it is even possible to calculate the altitude.
How accurate and how reliable is GPS?
Modern GPS devices are considered very reliable. A typical GPS receiver has an accuracy of up to a few meters. This depends on how many satellites can be received and in which constellation they are located.
GPS is almost independent of weather conditions. Even in dense clouds and rain, the signal reaches the device without any problems. Only heavy snowfall or closed rooms disturb the GPS reception. Valleys, forests, or buildings weaken the reception and therefore also the accuracy. In dense forests, you can lose the reception for some time or the signal becomes less accurate.