GPS stands for Global Positioning System. The GPS is actually the 27 satellites that orbit the Earth and the thing we use for directions is the GPS receiver. The receiver uses a mathematical technique called trilateration, in which it finds at least 4 of the satellites, finds the distance from each, and figures out its location in 3-dimensional space. It creates spheres around designated points, based on where the satellites above you are and how far away from them you are. Where the spheres intersect is where you are (see below). The receiver figures this out by using radio signals from the satellites.
To calculate the distance between the GPS receiver and the GPS satellite, it starts off with the satellite. At a specific time, the satellite starts transmitting a pseudo-random code and at the same exact time the receiver starts running the same exact code. When the satellite's code gets to the receiver, it will be lagging behind. The receiver takes the length of this lag, multiplies it by the speed of light, and determines how far the signal traveled.
The receiver has the predicted location of the satellites at any given time stored in an almanac. Once the receiver has calculated your location, it plugs the latitude and longitude into map files stored in its memory, making GPS usage more user-friendly. GPS receivers can also track your location as you move, constantly in communication with the satellites. This can provide you with information about your speed, how far you've traveled, how long you've been traveling, your ETA, etc. How rad is it that we can communicate so quickly with satellites that are orbiting the Earth?! The answer is super rad!!
References:
http://electronics.howstuffworks.com/gadgets/travel/gps.htm
http://stackoverflow.com/questions/33637/how-does-gps-in-a-mobile-phone-work-exactly
You're so right, this is super rad!! So crazy how what seems like such a complicated process can happen so quickly when we need directions or need to locate something. What would cause a GPS location to be a bit off of your actual location? Is it something like the circles don't intersect at the right point, or is it just that there is a lag in information? Cool article!
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