Automobile manufacturers are offering moving-map displays guided by GPS receivers as an option on new vehicles. Several car companies are demonstrating GPS-equipped vehicles that give directions to drivers on display screens and through synthesized voice instructions.
GPS in navigation( what is navigation?) Since prehistoric times, people have been trying to figure out a reliable way to tell where they are, to help guide them to where they are going, and to get them back home again. Cavemen probably used stones, when they set out hunting for food. These marks used to erase no. of times. The earliest mariners followed the coast closely to keep from getting lost. The next major developments in the quest for the perfect method of navigation were the magnetic compass and the sextant. The needle of a compass always points north, so it is always possible to know in what direction you are going. The sextant uses adjustable mirrors to measure the exact angle of the stars, moon, and sun above the horizon. However, in the early days of its use, it was only possible to determine latitude( the location on the Earth measured north or south from the equator) from the sextant observations. Sailors were still unable to determine their longitude( the location on the Earth measured east or west). In 1761, a cabinetmaker named John Harrison developed a shipboard timepiece called a chronometer, which lost or gained only about one second a day- incredibly accurate for the time. For the next two centuries, sextants and chronometers were used in combination to provide latitude and longitude information.
In the early 20th century several radio-based navigation systems were developed, which were used widely during World War II. A few ground-based radio-navigation systems are still in use today. One drawback of using radio waves generated on the ground is that you must choose between a system that is very accurate but doesn’ t cover a wide area or one that covers a wide area but is not very accurate. High-frequency radio waves( like UHF TV) can provide accurate position location but can only be picked up in a small, localized area. Lower frequency radio waves( like AM radio) can cover a larger area, but are not accurate.
Scientists decided that the only way to provide coverage for the entire world was to place high-frequency radio transmitters in space. A transmitter high above the Earth sending a high-frequency radio wave with a special coded signal can cover a large area. This is one of the main principles behind the GPS system.
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