Published on : 20 April 20223 min reading time
The GPS satellites
The GPS geolocation system operates with 24 satellites, placed in a nearly circular orbit at an altitude of about 20 200 km. After several years of launches, their revolutions around the earth have been estimated so that at least four satellites can be seen continuously from any point on the earth. Click here to read more. The speed of the satellite is close to 14 000 km / h. The lifespan of the satellite is about 8 years. All satellites currently in use are second or third generation.
The car GPS is actually a receiver that can analyse the signals sent by satellites. It uses the principle of triangulation. In fact, in order to calculate its position, it receives a signal from the first satellite, which will indicate the distance separating it from this one by calculating the time necessary for this signal to arrive. This time is calculated as a function of the signal transmission time and the reception time. It should be noted that a synchronisation between the satellite and the GPS has already taken place in order to match their internal clocks. At this point, the vehicle’s GPS does not yet know its location or position. However, it does know the distance to the satellite. Then it receives the signal from the second satellite, and the second satellite will also give its distance, then a third satellite will also give its distance and so on until the fourth satellite. Thus, at least four satellites are needed to cross-reference the signal and determine its geographical position.
What is important to remember is that one of the difficulties that can arise in the geolocation of vehicles, particularly in synchronisation, is due to the fact that the satellites have very precise atomic clocks that GPS receivers do not have. In this case, please note that an error of one millionth of a second can lead to a position shift of about 300 metres. Another difficulty is the attenuation of the signal as it passes through the earth’s atmosphere. Under all these constraints, satellite and GPS systems take errors into account and integrate the results of the correction through complex mathematical calculations.
The components of fleet geolocation
Geolocation hardware and software makes vehicle fleet management easier. Also known as a telematics unit, the GPS tractor uses the satellite network to record the position of vehicles and transmit information in real time via GSM/GPRS networks. Several sensors connected to the on-board device can also be installed on the vehicle to collect more data such as temperature, power take-off, etc. As for the geolocation software, it allows the entire fleet to be viewed in real time on the map, and the information collected from the vehicle to be reconstructed in the form of reports and graphs so that the data can be interpreted.