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Global Positioning System

Global Positioning System. How to know exactly where you are when you’re lost. What is GPS?. The Global Positioning System (GPS) is a satellite-based navigation system created by the U.S. Department of Defense.

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Global Positioning System

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  1. Global Positioning System How to know exactly where you are when you’re lost.

  2. What is GPS? • The Global Positioning System (GPS) is a satellite-based navigation system created by the U.S. Department of Defense. • GPS satellites orbit above the Earth and transmit signals that can be detected by anyone with a GPS receiver.

  3. Satellite Constellation • 24 satellites transmitting signals. • Six satellites can be “seen” at any time, anywhere on Earth. • An atomic clock in each satellite ensures extremely accurate measurements.

  4. User Receiving Equipment • In order to calculate your location, then, the GPS receiver needs two things: • The location of at least three satellites above you • The distance between you and each of those satellites • The GPS receiver calculates both of these things by analyzing radio signals from the GPS satellites. • The receiver can then figure out how far the signal has traveled by timing how long it took the signal to arrive.

  5. How GPS Works Trilateration • Let's say that you are somewhere in the United States and you are TOTALLY lost -- you don't have a clue where you are. • You find a friendly-looking person and ask, "Where am I?" and the person says to you, "You are 625 miles from Boise, Idaho.“ • You could be anywhere on a circle around Boise that has a radius of 625 miles.

  6. How GPS Works Trilateration • So you ask another person, and he says, "You are 690 miles away from Minneapolis, Minnesota." • This is helpful -- if you combine this information with the Boise information, you have two circles that intersect. • You now know that you are at one of two points, but you don't know which one.

  7. How GPS Works Trilateration • If a third person tells you that you are 615 miles from Tucson, Arizona, you can figure out which of the two points you are at. • GPS receivers work in a similar way by getting the distance from at least 3 satellites. • A 4th satellite is needed for error correction.

  8. How GPS Works • In 3-Dimensions your GPS unit determines you could be anywhere on a sphere. • 3 satellites leave you with 2 possible locations – 1 of which is usually impossible.

  9. Applications Military (targeting, troop placement) Agriculture & Construction Fishing & Hunting Surveying, Mapping, & GIS Transportation (Aircraft, Marine, Rail) Location Based Services (cell phones, wireless web) Tracking Systems Package/Asset (UPS/FedEx, semi-trucks, rental cars) Public Safety (emergency vehicle routing, parole/probation) Geo-Caching (GPS scavenger/treasure hunts)

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