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GPS in Land Surveying

GPS in Land Surveying. Evergreen Valley College Engineering and Engineering Technology H. Johnston, T. Redd, A. Tabrizi July 12, 2005. Today’s Topics . Part I Background Information Accuracy and Precision What is GPS? Why and who uses it? How does it work? GPS Surveying – The Basics

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GPS in Land Surveying

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  1. GPS in Land Surveying Evergreen Valley College Engineering and Engineering Technology H. Johnston, T. Redd, A. Tabrizi July 12, 2005

  2. Today’s Topics • Part I • Background Information • Accuracy and Precision • What is GPS? • Why and who uses it? • How does it work? • GPS Surveying – The Basics • Part II • GPS Surveying Techniques • Mission Planning and Design • Part III • Field Exercises • Post Processing Field Data • Advanced Topics

  3. GPS Course Information • Lecture component: • Accuracy, precision, & error • Oral & written communication • Introduction to GPS • Laboratory component: • Field activities • Data processing • Expected learning competencies AHT/EVC

  4. HHistory of Measurement & • DDevices • Mechanical • Opto-Mechanical • Electronic • Electronic Distance Measuring • Total Station • Satellite Assisted Systems

  5. Mechanical & OpticalDevices • Simple to use • Usually cheap • Poor accuracy • Simple applications • Poor productivity • Poor practicality AHT/EVC

  6. Some Oldies AHT/EVC

  7. Some Oldies AHT/EVC

  8. Some Oldies AHT/EVC

  9. Some Oldies AHT/EVC

  10. Some Oldies AHT/EVC

  11. Some Oldies AHT/EVC

  12. Some Oldies AHT/EVC

  13. Some Oldies Wireless Communication Technology AHT/EVC

  14. Two-way ranging by EDM D one clock used to measure t d D Two way travel time: t=2d/c. D Distance: d=c t/2 Electronics Devices • Electronic Distance Meter AHT/EVC

  15. Total Station AHT/EVC

  16. Satellite Assisted • Celestial satellites (not electronic) • Navy Navigation Satellite System (NNSS) or TRANSIT (5 to 7 satellites at 1100 km polar orbits. Provided navigational help to the US Navy's Polaris submarine fleet. • NAVigation Satellite Timing and Ranging (NAVSTAR) AHT/EVC

  17. AHT/EVC

  18. Accuracy and Precision • Accuracy: Degree of perfection obtained in any measurement, i.e. closeness to the actual value • Precision: Degree of refinement of measurement, i.e. degree of repeatability or consistency of a group of observations • Both are important in Surveying AHT/EVC

  19. Accuracy & Precision Good Precision Poor Precision Good Precision Good Accuracy Good Accuracy Poor Accuracy AHT/EVC

  20. Can Hi-Tech Equipmentbe Trusted? • Accuracy and precision may be improved: • If we follow directions • If we stay within the operating limits of the equipment • If we use the equipment properly • If we use the right equipment for the job • If we use care and preplanning • If we build redundancies into the measurement • If we can trust the people who are using the equipment! So nothing is new here! Hi-tech or not, we still need to use caution. AHT/EVC

  21. What is a GPS? Definitions AHT/EVC

  22. What is GPS? • A system capable of providing position information anywhere on earth – Global Positioning System • A constellation of orbiting satellites • Various orbits around the earth • NAVSTAR GPS • User receivers acquire signal and determines its position AHT/EVC

  23. GPS • Global Positioning System • Developed by DOD • Cost $10 billion • Triangulation-based technology AHT/EVC

  24. Why use it? • AAA (who can resist it!) • All weather operation • Always available (24/7 operation) • Anywhere available • Economical • Increased Productivity • Improved Customer service • Accuracy (3-D data, Velocity and timing) AHT/EVC

  25. Who Uses it? • Land, sea, and airborne navigation, surveying, geophysical exploration, mapping and geodesy, vehicle location systems, farming, transportation systems • Telecommunication infrastructure applications include network timing and enhanced 911 for cellular users • Global delivery of precise and common time to fixed and mobile users AHT/EVC

  26. Some Applications AHT/EVC

  27. Some Applications Could be used to track mail if properly used! AHT/EVC

  28. Some Applications AHT/EVC

  29. Some Applications AHT/EVC

  30. Some Applications AHT/EVC

  31. Some Applications AHT/EVC

  32. Some Applications AHT/EVC

  33. Some Applications AHT/EVC

  34. Some Applications AHT/EVC

  35. Some Applications Mapping AHT/EVC

  36. How does The GPS work? • The GPS System Components • The User Segment • The Control Segment • The Space Segment AHT/EVC

  37. The GPS System Components AHT/EVC

  38. The User Segment • GPS user equipment – portable and fixed • Military • Civilian • Navigation • Surveying • GIS AHT/EVC

  39. The Control Segment • Ground facilities responsible for • satellite tracking • telemetry • orbit & ephemeris computations • uplinking of the computed data • supervising the daily management of the space segment • Five ground control stations (Monitor Stations) • One Master Control Station AHT/EVC

  40. Master Control Station • Receive tracking data from the monitor stations • Calculates satellites ephemeris • Adjusts satellite clocks • Maneuvers satellites, if needed • Encrypts signals • Maintains GPS reference system (WGS84) AHT/EVC

  41. The Space Segment AHT/EVC

  42. The Space Segment • Constellation of 24 Satellites • In six orbital planes around the equator (60 degrees apart) • Four satellite per orbit • Orbital planes inclined 55 degrees from the equator AHT/EVC

  43. Satellite Constellation AHT/EVC

  44. GPS Satellite • Seven satellites are typically visible 10 degrees or more above the horizon • Each satellite is about 2 to 3K lbs • Satellites orbit the earth every 12 hours • Time can be figured to within 100 nanosecs AHT/EVC

  45. GPS Satellite • BLOCK IIA SATELLITE CHARACTERISTICS • Weight (in orbit): 2,175 pounds • Orbit altitude: 10,988 nautical miles • Power source: solar panels generating 700 watts • Dimensions: 5 feet wide, 17.5 feet long (including wing span) • Design life: 7.5 years AHT/EVC

  46. GPS Satellite • BLOCK IIR SATELLITE CHARACTERISTICS • Weight (in orbit): 2370 pounds • Orbit altitude: 10,988 nautical miles • Power source: solar panels generating 1136 watts • Dimensions: 5 feet wide, 6.33 feet in diameter, 6.25 feet high (38.025 feet wide including wing span) • Design life: 10 years AHT/EVC

  47. GPS Satellite • BLOCK IIF SATELLITE CHARACTERISTICS • Weight (in orbit): 3758 pounds • Orbit altitude: 10,988 nautical miles • Power source: solar panels generating up to 2900 watts • Dimensions: 8 ft x 6.47 ft (stowed) 70.42 ft (deployed 4 panel solar arrays) x 12 ft • Design life: 15 years AHT/EVC

  48. GPS Satellite AHT/EVC

  49. What is so special about an 11,000 mile orbit? • Mathematically perfect orbit • ‘Orbits’ twice per day • Large ‘viewable’ area AHT/EVC

  50. Basic Concept • Satellites are reference points to locations on earth (their location are known) • A location of a point on earth is identified by “triangulation” • Signals from three satellites are used • Travel time of each signal is determined • Signals travel at Speed of light • Distance = Travel Time * Speed of Light AHT/EVC

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