TRACKERS IN THE SKY
AIDED BY GRID OF SATELLITES ORBITING THE EARTH, GLOBAL POSITIONING SYSTEM TELL US WHERE WE ARE AND WHERE WE HAVE TO GO.
In case you are lost with no clue of where you are, getting directions could tend to be a bit tricky. But you will be saved the bother of such an eventuality if you have a GPSenabled mobile in your hand or a GPS system in your car. With these devices it is easy to figure out where you are and get turn-by-turn directions to your destination.
Like a cell phone, a GPS receiver relies on radio waves. But instead of using towers on the ground, it communicates with satellites that orbit the Earth. There are currently 27 GPS satellites in orbit —24 are in active use, with the rest meant as backup in case one or the other fails.
In order to determine your location, a GPS receiver has to determine:
The locations of at least three satellites above you
Where you are in relation to those satellites.
The receiver then uses trilateration to determine your exact location on earth. Basically, it draws a sphere around each of the three satellites it locates. These three spheres intersect at two points—one in space, and one on the ground. The point on the ground where the three spheres intersect is your location.
However, GPS isn’t foolproof. GPS receivers use a combination of signals from a network of satellites and ground stations to figure out where you are and where you’d like to go. It is really only as good as the satellite network and its map data. Without a clear and strong signal, your device can’t accurately establish your location. Tall buildings, dense foliage, mountains and even reflective objects can cause errors.