GPS stands for Global Positioning Service. GPS allows people to use an electronic unit to determine their exact location (within a margin of error) on the globe using satellite technology originally developed by the government. While not a new technology, its availability and usage by the general public is newer and thus somewhat misunderstood.
There is no subscription fee to use a GPS unit, once you purchase the unit you can use GPS indefinitely. GPS is only one of three worldwide satellite positioning services. There is one run by the European Union as well as one run by the Russian Federation. The one run by the Russians is similar to GPS and is in usage, but the EU's only began in 2005 and has yet to reach its full capability.
GPS satellites are used to determine the exact location of the GPS unit. These satellites orbit the Earth twice a day in a specific orbit which is maintained by a rocket pack that helps keep the satellites on course. They are solar powered with batteries to help in the course of a solar blackout.
They orbit at a height of about twelve thousand feet above the Earth at a speed of about seven thousand miles and hour. The time between when the GPS unit sends the signal and it is received by the satellite is used to determine how far away the satellite is. Three of these measures is used to pinpoint the location.
Three satellites are used to give the longitude and latitude readings. If a fourth satellite is in view it is also possible to get the altitude reading. Once the unit's position is found other readings can be calulated such as speed, distance to a destination, and bearing. The average GPS unit is accurate to about fifteen meters, although this can be made more accurate with the usage of additional technology. The usage of Wide Area Augmentation System (WAAS) can improve the accuracy to less than three meters and is generally available on newer GPS units.
Differential GPS (DGPS) can also be used to improve the accuracy to about three to five meters. The most common DGPS is run by the US Coast Guard and is a system of towers and beacons. They receive the GPS signal and broadcast a corrected signal.
The use of DGPS requires additional equipment. The uses of GPS units are are varied as the people who use them. They are included in many phones and cars and can help give directions or be used to find missing people. Hikers and campers can use GPS to make sure they are really on the right trail, saving them walking further or getting completely lost. GPS in cars can give accurate directions to addresses and some can even pull up business listings to help you find where you need to be going.
Whats more is they can help you find the best route there based on traffic patterns and driving conditions. They are also used to contact emergency assistance and locate the user.
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