# Thank you Albert Einstein for making our GPS work!

## The GPS position of LiDAR drones uses the General relativity, a theory of gravitation that was developed by Albert Einstein between 1907 and 1915.

In order to understand this sentence, it is important to remember how a Global Positioning System (GPS) works.

Satellites orbiting the Earth transmit information about their position and current time at regular intervals. The GPS receiver on Earth calculates its distance to each satellite by calculating the time difference between the time of departure and the time of arrival of the signal. The distance is equal to the travel time multiplied by the speed of light. A GPS receiver needs only to receive signals from a minimum of three satellites for it to be located in space by trilateration (i.e. triangulation + distance).

What does this have to do with relativity?

Each satellite has an atomic clock that gives it the exact time. However, Albert Einstein explains that time flows more slowly under the effect of strong gravitational attraction. Time on board the satellite flows faster than on Earth (because the Earth’s attraction is weaker). The calculation of distance from the time of departure and the time of arrival of the signal emitted by the satellite must take this effect into account. If we did not take this effect into account, the GPS indication would shift by about ten kilometres per day! 