The satellites
The US GPS constellation has around 30 operational satellites orbiting at about 20,200 km. Other systems, including Europe's Galileo, Russia's GLONASS and China's BeiDou, work in the same way. Modern receivers often use several systems at once.
Working out a position
Each satellite broadcasts its position and a highly accurate time signal. The receiver measures how long each signal took to arrive, works out its distance from each satellite and calculates its own position. This is called trilateration. Four satellites are needed to solve for latitude, longitude, altitude and the receiver's clock error.
From position to tracking
- The tracker records position, time, speed and heading
- It sends this data to a server over 2G, 4G LTE-M or NB-IoT networks
- The platform stores the data and shows it on maps and in reports
- Alerts are triggered when rules are met, such as leaving a geofence
GPS navigation versus GPS tracking
A sat-nav only receives satellite signals and shows you where you are. A tracker also transmits that position so someone else can see it.