How does Global Positioning System work?

Question

How does Global Positioning System work?

Answer 1

Each GPS satellite transmits data that indicates its location and the current time. All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant. The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times because some satellites are farther away than others. The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver. When the receiver estimates the distance to at least four GPS satellites, it can calculate its position in three dimensions.

There are at least 24 operational GPS satellites at all times. The satellites, operated by the U.S. Air Force, orbit with a period of 12 hours. Ground stations are used to precisely track each satellite's orbit.





Determining Position

A GPS receiver "knows" the location of the satellites, because that information is included in satellite transmissions. By estimating how far away a satellite is, the receiver also "knows" it is located somewhere on the surface of an imaginary sphere centered at the satellite. It then determines the sizes of several spheres, one for each satellite. The receiver is located where these spheres intersect.



Bottom Line: u need at least 3 satellites to get the 3 unknowns X, Y, Z of ur location

Answer 2

Hmmm. How much time do you have?



There are entire departments in the American Government dedicated to maintaining the GPS constellation. It is actually fairly complicated, but here's the short answer.



Your GPS unit receives signals from sattelites. Since the position of the sattlites is predictable, it is a simple calculation to determine exactly where they are. The unit has to receive signals from at least three so that it can find it's own position relative to them, and then viola! it knows where you are.



Your position is then overlayed on a pre-loaded map of your area, and there is an additional process to determine your altitude, but it's essentially the same as the above.

Answer 3

Very good answer from Anomaly, but actually there are four unknowns, so you need four satellites. The unknowns are the receiver's three spatial coordinates and the time error between the receiver's clock and so-called "GPS time," which is the very accurate synchronized time of all the satellites' clocks. If the receiver can only get signals from three satellites, then it can only compute two of the three spatial coordinates (which is sometimes good enough, because those can be chosen to be latitude and longitude -- thus not getting altitude).

Answer 4

Unfortunately virtually all technical advancements have come as a result of war. Google global positioning system, come on man.

Answer 5

The website given by Anomaly is much informative.Thanks to Anomaly.









http://www.nasm.si.edu/gps/work.html...