The Global Positioning System, commonly called GPS, is a navigational system
that uses satellites and computers to determine the latitude and longitude of a
receiver on Earth. This is done by computing the time difference for signals
from different satellites to reach the receiver.
GPS is the only satellite navigation system that is fully functional. It uses
a collection of more than twenty-four satellites to send radio signals to
electronic GPS receivers. By doing so, the satellites are able to find the
correct location of the receivers. They get the exact longitude, latitude and
altitude of the receiver. GPS systems work around the clock under any weather
conditions.
The GPS system became fully functional in 1985. Today it is used for
navigating on land, sea and air. It is also used for mapmaking, land surveying
and scientific research.
Over the last fifteen years, the accuracy of the GPS signal has improved
steadily. Today, a GPS system can accurately pinpoint the receiver on Earth to
almost five meters of its exact location. However, further improvements and
developments may increase the accuracy to about 1 cm of the receiver. This can
be done using techniques such as differential GPS. A GPS also gives an extremely
precise time reference which is useful in some scientific experiments.
The GPS system was devloped by the United States Department of Defense. It
was officially named NAVSTAR GPS, which was an abbreviation for Navigation
Signal Timing and Ranging Global Positioning Systems. Out of the twenty-four
satellites revolving around the Earth, the last one was launched in 1994. New
satellites are periodically launched to replace aging ones. With the improvement
in technology, GPS devices have become less costly. GPS is available for free
use in civilian applications.
