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Global Positioning System

Global Positioning System. An easy to use technology for everyone By Dr. Badruddin, CCC. What is GPS ?. A very precise positioning system. Developed and maintained by the US Department of Defense (DOD). Satellite Based * 24 satellites * 20,200 km high orbit. BUT!.

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Global Positioning System

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  1. Global Positioning System An easy to use technology for everyone By Dr. Badruddin, CCC

  2. What is GPS ? A very precise positioning system • Developed and maintained by the US Department of Defense (DOD) • Satellite Based • * 24 satellites • * 20,200 km high orbit

  3. BUT! Although it is a very precise geographic positioning system • It is very easy to get youself into trouble • Why? • Because you (probably) don’t understand how it works • And that leads to garbage

  4. Free • Precise • Reliable • All weather • Anytime & anywhere • Unlimited user capacity Characteristics of GPS Accurate(precise) Almost!

  5. Segments of GPS 1. Space Segment A constellation of 24 satellites 2. Monitor Station A network of earth-based facilities 3. Users & Equipment Source:Trimble

  6. Segments of GPS 1. Space Segment A constellation of 24 satellites Source:Trimble

  7. GPS Monitoring Station

  8. How GPS Works ……… Uses measurements from 4+ satellites Distance = travel time x speed of light Source:Trimble

  9. + Satellite A + Satellite B Determining GPS Position • Suppose the distance from Satellite A to our position is 11,000 miles • At this point we could be located anywhere on the specified sphere • Next, let us take another measurement from a second satellite, Satellite B • Now our position is narrowed down to the intersection of theses two sphere

  10. + + Satellite C Satellite A + Satellite B Determining GPS Position • Taking another measurement from a 3rd satellite narrows our position down even further, to the two points • These points are located where the 3rd sphere cuts through the the intersection of first two spheres • So by ranging from 3 satellites we can narrow our position to just two points in space

  11. + + Satellite C Satellite A + Satellite B How do we decide which one is our true location? • We could make a 4th measurement from another satellite to determine the true point OR • We can eliminate one of the two points that gives a ridiculous answer • The ridiculous point may be too far from the earth • However, GPS receivers use a 4th satellite to precisely locate our position

  12. Determining GPS Position

  13. Time spent on measurement • Design of receiver • Postprocessing • Relative positions of satellites, technically known as PDOP(Position dilution of precision) How accurate is GPS? Depends on some variables

  14. GPS Receivers

  15. Mostly used for recreational purposes GeoXT Versus Garmin Mostly used for GIS data collection

  16. 10-20 m 2-5m cm Methods of data collection Three methods of positioning • Autonomous • 10-20 meters • Differential • 2-5 meters • Phase Differential • centimeter

  17. Time spent on measurement • Design of receiver • Postprocessing • Relative positions of satellites, often known as DOP (Dilution of Precision) How accurate is GPS? Depends on some variables

  18. WAAS • Wide Area Augmentation System. • Itprovides FREE GPS differential correction data for visible satellites • Developed & operated by the FAA (Federal Aviation Administration) for flight navigation but it’s available free to GPS users • WAAS-enabled receivers can provide sub-meter level accuracy anywhere in most locations of the US and southern Canada.

  19. WAAS • Differential corrections are computed from ground stations and then uploaded to geostationary satellites for broadcasting • WAAS-enabled GPS receiver automatically uses such correction data to enhance the positional accuracy

  20. Multipath PDOP SNR Sources of error Source:Trimble

  21. Multipath • When GPS signals arrive at the receiver having traveled different paths

  22. PoorPDOP GoodPDOP What is a PDOP? • Position Dilution of Precision

  23. Signal Strength Indicators SNR (signal-to-noise ratio) • SNR determines the signal strength relative to noise • GPS position is degraded if the SNR of one or more satellites in the constellation falls below certain range

  24. Cycle through pages Scroll keypad Goto PAGE On/Off switch Save a waypoint MARK Quit ENTER UsingGarmin12

  25. Common use of GPS • GIS data collection & mapping • B. Navigation • C. Recreation

  26. GPS forNavigation

  27. GPS forNavigation • GPS in PDA • Are getting popular in car • Comes with voice guidance

  28. GPS inrecreation

  29. GPS in Farmland

  30. A. GPS in USA B. GLONASS program from Russia C. GALILEO from European countries Future GPS

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