Global positioning system
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GPS is a satellite-based navigation system that provides precise geographic positioning anywhere in the world. It uses a constellation of 24 satellites in medium Earth orbit that transmit signals allowing GPS receivers to determine their latitude, longitude, and elevation. The system is maintained by the US Department of Defense and provides free and accurate positioning to unlimited civilian users globally. GPS works by precisely measuring the time it takes signals from four or more satellites to reach a GPS receiver, allowing the device to calculate the user's position by triangulating the distances to the satellites. With factors like receiver quality, satellite geometry, and signal processing, positions can be accurate to within a few meters for most applications.
Global positioning system
- 1. GLOBAL POSITIONING SYSTEM Prepared By : Patel Jay C ME(EC)-140870705004 An easy to use technology for everyone
- 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 yourself into trouble •Why? •Because you (probably) don’t understand how it works •And that leads to garbage •Now First We learn the prerequisite terms
- 4. Latitude What is Latitude? • Lines of Latitude run horizontally • Latitude is measured in degrees. • The Equator is 0 degrees Latitude. • Lines of Latitude locate places North or South of the Equator. • The North Pole is 90 degrees N Latitude, and the South Pole is 90 degrees S Latitude.
- 5. Longitude • Lines of Longitude run vertically. • They are also called Meridians. • The Prime Meridian is found in Greenwich, England. • The Prime Meridian is 0 degrees Longitude. • Lines of Longitude locate places East or West of the Prime Meridian. • There are 180 degrees of east Longitude, and 180 degrees of west Longitude.
- 6. Characteristics of GPS • Free • Precise • Reliable • Anytime & anywhere • All weather • Unlimited user capacity Almost!
- 7. 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
- 8. Segments of GPS 1. Space Segment A constellation of 24 satellites
- 10. How GPS Works ……… Uses measurements from 4+ satellites Distance = travel time x speed of light Source:Trimble
- 11. 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 Satellite A + • Next, let us take another measurement from a second satellite, Satellite BSatellite B + • Now our position is narrowed down to the intersection of theses two sphere
- 12. Satellite C + Determining GPS Position Satellite A Satellite B + + • Taking another measurement from a 3rd satellite narrows our position down even further, to the two points • So by ranging from 3 satellites we can narrow our position to just two points in space • These points are located where the 3rd sphere cuts through the the intersection of first two spheres
- 13. Satellite C + How do we decide which one is our true location? Satellite A Satellite B + + • We could make a 4th measurement from another satellite to determine the true point • However, GPS receivers use a 4th satellite to precisely locate our position • We can eliminate one of the two points that gives a ridiculous answer • The ridiculous point may be too far from the earth OR
- 15. How accurate is GPS? Depends on some variables • Design of receiver • Relative positions of satellites, technically known as PDOP (Position dilution of precision) • Postprocessing • Time spent on measurement
- 16. GPS Receivers
- 17. GeoXT Versus Garmin Mostly used for GIS data collection Mostly used for recreational purposes
- 18. How accurate is GPS? Depends on some variables • Design of receiver • Relative positions of satellites, often known as DOP (Dilution of Precision) • Postprocessing • Time spent on measurement
- 19. WAAS • Wide Area Augmentation System. • It provides 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.
- 20. 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.
- 22. Multipath • When GPS signals arrive at the receiver having traveled different paths
- 23. What is a PDOP? • Position Dilution of Precision Good PDOP Poor PDOP
- 24. 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 Signal Strength Indicators
- 25. Common use of GPS A. GIS data collection & mapping B. Navigation C. Recreation
- 27. GPS for Navigation • GPS in PDA are getting popular in car comes with voice guidance.
- 29. GPS in Farmland
- 30. Future GPS A. GPS in USA B. GLONASS program from Russia C. GALILEO from European countries