# How Does GPS work?

Discussion in 'General GPS Discussion' started by Nuvi-Nebie, Jan 28, 2017.

Not open for further replies.
1. ### Nuvi-NebieModerator

Joined:
Aug 16, 2015
Messages:
2,099
180
Location:
UK
This is a simplified explanation of how GPS works, it is not meant to explain the full complexities of the system

1) There are 24 GPS satellites* tracking around the earth (Max.12 visible from a point on earth)
2) The satellites carry very accurate atomic clocks
3) The satellites don't know where your GPS is, but they do know which bit of the earth they are above
4) Each satellite transmits the current time, it's location above earth and height above Earth
5) A GPS can synchronize it's internal clock to the time sent from the satellites

* The GPS constellation of satellites is now joined by other constellations such as Glonass, BeiDou, Galileo etc.

As the GPS's clock is now (almost) as accurate as an atomic clock, it can calculate the distance from itself to the satellite by using the signal time delay, for example, if the time stamp from a satellite arrives at the GPS a tenth of a second after it was sent, the distance to the satellite would be roughly 18600 miles, (the signal travels at the speed of light)

Using trigonometry and the distance from four or more satellites, the GPS can calculate where is it, using the three dimentional positions of the satellites and their distances to the GPS, each distance becomes the radius of a sphere drawn in space, that converge on the GPS's location  For a far more detailed (and complicated ) explanation of how GPS works take a look at "Understanding GPS Principles and Applications"

Nuvi-Nebie, Jan 28, 2017
Jacob Ethan, Nazish and Ian like this.