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Introduction to GPS and mapping

Introduction to GPS and mapping. Global Positioning System. What is GPS ?. Department of Defense developed for navigation Standard positioning service (public uses) Precise positioning service Launches began in 1970s Full operational capability in mid 1990s

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Introduction to GPS and mapping

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  1. Introduction to GPS and mapping

  2. Global Positioning System What is GPS?

  3. Department of Defense developed for navigation • Standard positioning service (public uses) • Precise positioning service • Launches began in 1970s • Full operational capability in mid 1990s • ‘Selective Availability’ turned off 2000 • Degraded accuracy to ~100m History of GPS

  4. Space segment – (satellite life = 10 years) • Several generations of satellites in use now • Control segment • User segment • US spends $400,000,000 yearly • Free to you – tax dollars at work again • Other countries operate their own systems too GPS system

  5. Space Segment • 24 satellites with spares in 6 orbital planes (4 in each) • ~12,500 miles elevation • 55 degree inclination • Each one circles Earth every 12 hours (7000 mph) • At least 4 visible at every point on the earth at all times

  6. Master Control Station (MCS) in Colorado • 5 Monitoring stations • Ground control stations (Ground Antennas) • Unmanned • Enable MCS to control the satellites Control Segment

  7. Antenna Receiver Base map Record tracks, waypoints, distance User Segment

  8. Triangulation Need D+1 satellites to determine position = 2D needs 3 satellites, etc How does it work?

  9. Sources of error ionosphere • Dual frequency mode of more advanced receivers corrects

  10. Sources of error - Satellite geometry Geometric Dilution of Precision (GDOP) – the higher the value, the poorer the measurement (very good = <4, bad = >6)

  11. Sources of error multipath

  12. Recreation grade = ~8m • Mapping grade = <1m • Survey grade = several cm • Accuracy versus Precision • Accurate measurement versus true location • Precise measurements close to each other How accurate?

  13. Post Processing – 2 to 5 M

  14. Mapping overview

  15. Geodetic surveying (magnetic) (Benchmarks) Surveying Methodology effects maps

  16. Declination Calculating Software Online Calculators Magnetic declination

  17. Geodetic Datums: What are they? • Define the size and shape of the earth • Used as basis for coordinate systems • Variety of models: • Flat earth • Spherical • Ellipsoidal • WGS 84 defines geoid heights for the entire earth

  18. Geographic Coordinate Systems (based on Datums) Latitude, Longitude of curved surface Projections make math easier USGS Map Projections Projected Coordinate Systems Cartesian (X, Y) with designated origin and distance from origin

  19. Projection and registration Datum used effects positional errors

  20. UTM coordinate system

  21. UTM is still not accurate enough for small area surveying. During 1930s, each US state adopt its own projection and coordinate system, generally known as State Plane Coordinates (SPC). Each state chose its own projection based on its shape to minimize distortion over the area of the state. Some states have more than one internal zone. The North American Datum 1983 (NAD83) is commonly used for SPC. State Plane Coordinates

  22. UTM conversion program

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