Global positioning system

GPS,mobile GPS,

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

9. GPS Monitoring Station

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 B Satellite 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 3 rd 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 3 rd 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 4 th measurement from another satellite to determine the true point However, GPS receivers use a 4 th 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

14. Determining GPS Position

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.

21. PDOP Multipath SNR Sources of error Source:Trimble

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 GIS data collection & mapping B. Navigation C . Recreation

26. GPS for Navigation

27. GPS for Navigation GPS in PDA are getting popular in car comes with voice guidance.

28. GPS in Recreation

29. GPS in Farmland

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