The Global Positioning System (GPS) consists of three segments - the control segment, space segment, and user segment. The control segment monitors the satellites and ground stations. The space segment is made up of 24 satellites that orbit the Earth. The user segment includes all GPS receivers on Earth. GPS uses trilateration to determine the precise position of receivers by calculating distances to multiple satellites. Sources of error include clock errors, atmospheric delays, and multipath interference. Error correction techniques like differential GPS improve accuracy. GPS has many applications including navigation, mapping, and timing systems. Its accuracy and uses are continuing to improve and expand.

1. GLOBAL POSITIONING SYSTEM By Migmar Dolma Anmol Bagga Nidhi Saxena

2. Contents What is GPS? Its segments How does it work? Calculations Sources of error Error corrections GPS Applications System performances Future of GPS GPS

3. What is GPS? Global Positioning System (GPS) is a radio based navigational system used to determine exact position. Developed by Dept of Defense at a cost of > $12 billion It is a “constellation” of 24 Earth-orbiting satellites that can provide continuous three-dimensional positioning 24 hrs a day throughout the world. GPS

4. 3 Segments of GPS Control Segment Space Segment User Segment Monitor Stations Ground Antennas Master Station GPS

5. 3 Segments of GPS CONTROL SEGMENT GPS The Control Segment consists of five monitoring stations (Colorado Springs, Ascension Island, Diego Garcia , Hawaii, and Kwajalein Island ), 3 out of which serves as the master control station. It is solely responsible for the construction, launching, maintenance, and virtually constant performance monitoring of all GPS satellites along with the Meteorological data . This data from the monitoring stations is then sent to the master control station for processing which involves the computation of satellite position , clock and orbital corrections GPS

6. GPS Ground Control Stations Currently there are only five GPS monitoring station that feed the Master Control Station. GPS

7. 3 Segments of GPS SPACE SEGMENT It consists of the Constellation of NAVASTAR earth orbiting satellites. They orbit at altitudes of about 12000, miles each, with orbital periods of 12 hours of 3-D position. Another satellite block , provides increased orbital accuracy. GPS

8. 3 Segments of GPS USER SEGMENT It consists of all earth-based GPS receivers. The typical receiver is composed of an antenna and preamplifier, radio signal microprocessor, control and display device, data recording unit, and power supply. It decodes the timing signals from the 'visible' satellites calculating their distances, latitude, longitude, elevation, and time. Their position is updated on a second-by-second basis, output to the receiver display device and stored by the receiver-logging unit. GPS

9. How does it work? The 3 parts involved in its working are: Satellites Receivers Softwares GPS

10. How does it work? SATELLlTES The Delta rockets launches these satellites from Cape Canaveral in Florida , United States . There are currently 27 GPS satellites in orbit -- 24 are in active use and 3 act as a backup in case another satellite fails. The orbits are tilted to the equator by 55° to ensure coverage in polar regions. The satellites are powered by solar cells to continually orientate themselves to point the solar panels towards the Sun and the antennas towards the Earth. Each satellite contains : Four precise atomic clocks Microprocessor on board for self-monitoring & data processing Thrusters which can be used to maintain or modify their orbits. GPS

11. How does it work? RECEIVERS A GPS Receiver relies on radio waves and communicates with satellites that orbit the Earth. In order to determine location, a GPS receiver has to determine: The locations of at least three satellites above you Where you are in relation to those satellites It makes use of Triangulation methods to get the exact position. GPS

12. 1D Triangulation Geometric Principle: You can find one location if you know its distance from other, already-known locations. But how to know your exact position on the circle? GPS

13. 2D Triangulation GPS

14. 3D Triangulation GPS

15. 3D Triangulation Triangulation in 3-D is the same as in 2D but instead of circles, you are working with spheres. Because of the added dimension four spheres are needed(the Earth acts as one). GPS

16. How does it work? SOFTWARES Even without a GPs device, we can still play interactively with a 3D texture mapped model of earth. It allows a user to upload and download waypoints, routes, orbit , and track routes by communicating with receiver. It manages the graphical data of GPs that makes possible the preparation, inspection and edition of GPs data in a friendly environment. It supports communication and real-time logging with receivers and accepts real-time logging information from any GPs receiver. GPS

17. How does it work? GPS

18. There and back again The distance from you to a satellite is calculated by the time that it takes for a radio wave to travel from the GPS unit to the satellite and then back to the GPS unit. D = V*t How long do you think that delay would be? GPS

19. What do you think? GPS 19000KM

20. Let’s do the calculation! If the satellites orbit 19,000 km from the surface of the earth, and the speed of light is 300,000 km/sec t = d/V = 2 * (19,000 km) / 300,000 km s -1 t = 0.127 s So these clocks have to be REALLY accurate, actually they are nuclear clocks. ? ? GPS

21. Sources Of Error Signals from satellites can be like light. When they hit some interference they sometimes bend a little and causes delays and bending due to refraction of signals. GPS

22. Sources Of Error Sometimes the signals bounces off even before they hit the receivers or follow multipath . GPS are Line of sight transmission which is the ability to transmit between two objects without any other objects getting in the way. GPS

23. Sources Of Error The dashed lines show the actual intersection point, and the gray bands indicate the area of uncertainty. The solid lines indicate where the GPS receiver "thinks" the spheres are located. Because of errors in the receiver's internal clock , these spheres do not intersect at one point. The GPS receiver must change the size of the spheres until the intersection point is determined. The relative size of each sphere has already been calculated, so if the size of one sphere is changed, the other spheres must be adjusted by exactly the same amount. GPS

24. Sources Of Error Wider spread gives better precision When the satellites are far away from each other, the area or uncertainty increases giving higher precision Satellite Distribution GPS

25. Sources Of Error All of this combines to make the signal less accurate, and gives it what we call a high “PDOP.” A PDOP of <4 is excellent A PDOP of 4-8 is good A PDOP of >8 is poor PDOP = Positional Dilution of Precision 11,000 miles 11,000 miles 11,000 miles 11,000 miles GPS

26. Error Correction Differential GPS (DGPS) GPS

27. Differential Correction Differential correction is a technique that greatly increases the accuracy of the collected GPS data. It involves using a receiver at a known location - the &quot;base station“- and comparing that data with GPS positions collected from unknown locations with &quot;roving receivers.&quot; GPS

28. In a Nutshell GPS

29. GPS Applications Locating and navigating Determining a basic position or monitoring the movement and getting from a known point to another. Geodesy Geodetic mapping (study of the shape of the earth and the determination of the exact position of geographical points) can be carried out effectively when helicopters were used or when the line of sight is not possible . Military Military applications include airborne, marine, and land navigation. Civil uses Telecommunication , surveying, aviation, maritime, agriculture, mining GPS

30. System Performances Standard Positioning System 100 meters horizontal inaccuracy 156 meters vertical inaccuracy Designed for civilian use No user fee or restrictions Precise Positioning System 22 meters horizontal inaccuracy 27.7 meters vertical inaccuracy Designed for military use GPS

31. Future of GPS It is an enabling technology with unlimited growth potential Currently more than 50 manufacturers of GPs receivers, with the trend continuing to be towards smaller, less expensive, and more easily operated devices. Current speculation envisions highly accurate, inexpensive, portable and equally accurate receivers and navigational guidance systems for automobiles. GPS management and technological innovations will make GPS surveying and navigation easier and more accurate. Supporting numerous civil applications never envisioned GPS

32. Bibliography WWW.HOWSTUFFWORKS.COM GOOGLE SCHOLOR BOOKS.GOOGLE.CO.IN WIKIPEDIA GPS