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.

Gadgets and Gizmos (India) - - TABLETS - TEXT AND GRAPH­ICS BY SAN­TOSH KUSH­WAHA

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.

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