How GPS systems work

In case you are lost with no clue of where you are, gettingdirections could tend to be a bit tricky. But you will be saved the bother ofsuch an eventuality if you have a GPS-enabled mobile in your hand or a GPSsystem in your car. With these devices it is easy to figure out where you areand get turn-by-turn directions to your destination.

Like a cell phone, a GPS receiver relies on radio waves. Butinstead of using towers on the ground, it communicates with satellites thatorbit the Earth. There are currently 27 GPS satellites in orbit-24 are inactive use, with the rest meant as backup in case one or the other fails.

In order to determine your location, a GPS receiver has todetermine:

• 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 exactlocation on earth. Basically, it draws a sphere around each of the threesatellites it locates. These three spheres intersect at two points-one inspace, and one on the ground. The point on the ground where the three spheresintersect is your location.

HOW GPS WORKS IN CARS

SOME SATELLITE FACTS The first GPS satellite was launched in 1978. A full constellation of 24 satellites was achieved in 1994. A GPS satellite weighs approximately 2,000 pounds and isabout 17 ft across with the solar panels extended. Their transmitter power is a mere 50 watts or less. There are some 2,500 satellites of all types and purposesorbiting the earth. Each GPS satellite is built to last about 10 years.

GPS car navigation systems can be factory-installed on newvehicles or purchased as an add-on accessory. Combining the use of signals fromthe satellites with interactive on-board maps, these systems can plot routes oftravel to a given destination based on a number of variables. Some of thesesystems are interconnected with sources of traffic information, enabling themto automatically account for congestion en route while determining the bestoptions to reach a destination.

If a driver misses a turn, these devices can quickly correctfor the error and present an updated route option. Providing voice or visualinstructions, these units also can help drivers find the nearest gas station orgive tips on restaurant or shopping options.

WHY DO GPS SYSTEMS GIVE WRONG DIRECTIONS?
However, GPS isn't foolproof. GPS receivers use acombination of signals from a network of satellites and ground stations tofigure out where you are and where you'd like to go. It is really only as goodas the satellite network and its map data. Without a clear and strong signal,your device can't accurately establish your location. Tall buildings, densefoliage, mountains and even reflective objects can cause errors.

Courtesy: Gadgets and Gizmos