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.
How GPS works
- 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.
HOW GPS WORKS IN CARS
GPS car navigation systems can be factory-installed on new vehicles or purchased as an add-on accessory. Combining the use of signals from the satellites with interactive on-board maps, these systems can plot routes of travel to a given destination based on a number of variables. Some of these systems are interconnected with sources of traffic information, enabling them to automatically account for congestion en route while determining the best options to reach a destination.
If a driver misses a turn, these devices can quickly correct for the error and present an updated route option. Providing voice or visual instructions, these units also can help drivers find the nearest gas station or give tips on restaurant or shopping options.
WHY DO GPS SYSTEMS GIVE WRONG DIRECTIONS?
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.
Courtesy:Gadgets and Gizmos