Physics

GPS - What It Is, How It Works


Which driver was never lost and was "saved" by a GPS? Since its inception, we can say that GPS is an indispensable tool for drivers, because in addition to identifying their location and guiding the routes to follow, it helps to control traffic, improve safety and the fluidity of traffic in general.

The acronym GPS stands for Global Positioning System, which in Portuguese means Global Positioning System. It is a technology that uses satellites and devices to provide location information on the globe. In addition to being widely used in cars, GPS has evolved and today offers some other functions that do not only concern location.


GPS (Global Positioning System)

The operation of technology

There are currently two systems that allow satellite navigation: The American GPS and the Russian GLONASS. Two other systems are being implemented: Galileo from the European Union and Compass from China.

The American GPS consists of a geographic positioning system that has a total of 24 satellites and 4 spare ones, in six planes near the orbit of planet Earth, at an altitude of 19,000 km.

It gives us the coordinates of a certain place on Earth as long as we have a GPS signal receiver. So that receiver, which we carry here on Earth, knows exactly where those satellites are.

These satellites are distributed so that a receiver, positioned anywhere on the earth's surface, will always be within reach of at least three of them (four or more for greater accuracy). Hence, localization is based on calculations that occur through a process called triangulation, illustrated below.


Triangulation from satellites is the basis of the GPS system.

In the triangulation process, three satellites send the signal to the receiver, which calculates how long it took each signal to reach it. In addition to its terrestrial location, the GPS receiver can also know the receiver's height from sea level, but a fourth satellite is required.

Both satellites and GPS receivers have a built-in clock that accurately marks the time in nanoseconds. When the satellite sends the signal to the receiver, the time it left the satellite is also sent.

By capturing satellite signals, the receiver calculates the distance between them by the time interval between the local instant and the instant the signals were sent. Taking into account the speed of propagation of the signal, the receiver can be at the intersection of this data, allowing to identify exactly where the device is on Earth.

In order for the receiver position to be always updated, the sending of these signals occurs constantly at a speed of 300 thousand kilometers per second (speed of light) in a vacuum.

From there, as the GPS receiver already knows where you are, it compares your location with a map (developed by the company that made the device), which will show you exactly where you have to go to get to your destination.

How did it come about

The US Department of Defense has created and maintained the GPS system since 1978, although it declared it fully operational only in 1995. At first, the US government decided that the civilian system would receive a less accurate signal with a margin of error in location about 100 meters, while the military would get a signal ten times more accurate.

GPS first came into play on a battlefield in the Gulf War (1990-1991), helping to guide soldiers in the desert. However, the US Army had few military-type GPS receivers and, to equip its troops, had to buy thousands of civilian devices.

Thus, the Department of Defense released the most accurate signal to all civilian receivers not to harm their soldiers. The restrictions, which came back after the war, only ended in 2000, when the government finally gave the precise signal to everyone.

Far beyond traffic

GPS is useful today in virtually every situation and profession where accurate location tracking is required, such as:
- flight and navigation vehicles
- exploitation of natural resources
- expeditions in woods or caves
- agriculture
- geology
- archeology
among others.

Prohibited Features

Currently, the same traffic regulation that authorizes the use of GPS, prohibits the installation of equipment capable of generating images for entertainment purposes to the driver. This is the case with multimedia centers available in most new cars.

Thus, the law states that if the system is installed at the front of the vehicle when the vehicle is in motion, it must have an automatic mechanism that renders it inoperative or switches it to the independent driver guidance information function. the wishes of the driver or passengers. Failure to do so results in a serious traffic violation. Installation for viewing rear seat occupants is permitted.

The same goes for digital TV, which should only work under the same conditions mentioned above.