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Exploring GPS and GIS Systems for Accurate Location Data

Learn about GPS satellites, accuracy, differential correction, and GIS applications for spatial data handling and mapping. Understand the importance of precise location data and the benefits of GPS and GIS technologies in various fields.

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Exploring GPS and GIS Systems for Accurate Location Data

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  1. Where we are going today… • GPS • GIS • Hey, there are exams next week. Oct. 4th and 6th. Powerpoints now online. www.uvm.edu/~jdavis6

  2. Global Positioning Systems

  3. GPS – Knowing Where You Are • Your location can be expressed in many ways: • Country, City, Province, Building Address, Office Number • Distance and Bearing from a Landmark • A referenced Coordinate System

  4. GPS Satellite Navigation System • Controlled by U.S. Department of Defense • Uses specially coded radio signals transmitted by 24 orbiting satellites • GPS receivers can use these radio signals to compute position, velocity, and time.

  5. GPS Constellation

  6. GPS Navigation

  7. GPS Satellite Signals

  8. GPS Accuracy • Before May 1, 2000 all SV signals were purposely degraded by the U.S Military. This degradation was called “Selective Availability.” Best uncorrected horizontal position was +/- 100 meters. • Selective Availability is now turned off. Best uncorrected horizontal position today is +/- 30 meters.

  9. Pseudo-Range Navigation

  10. Sources of Location Errors • Noise generated by the receiver circuits and noise from outside sources. Up to 2 meters • SV clock errors = 1 meter • Atmospheric delays = up to 11 meters • Multipath signals = 0.5 meters • User errors • Receiver software or hardware failure

  11. Dilution of Precision (DOP)

  12. GDOP Components • PDOP – Position Dilution of Precision (3D) • HDOP – Horizontal Dilution of Precision (Latitude and Longitude) • VDOP – Vertical Dilution of Precision (Height) • TDOP – Time Dilution of Precision

  13. PDOP Effected by Objects

  14. Differential Correction

  15. Survey-Grade GPS

  16. GPS Accuracy • Consumer Grade : 15 – 30 meters • Garmin, Magellan • No Post-processing • Mapping Grade : 1 – 5 meters • GeoExplorer III, CMT March III • Post-processing or real-time • Survey Grade : sub-meter • Post-processing or real-time

  17. GPS Data Format • The most current geodetic datum used for GPS is the World Geodetic System of 1984 (WGS84). • All GPS receivers export data in decimal degrees, WGS84

  18. How Accurate Do I Need? Accuracy of data depends on the application: • Property boundaries for land sales – Survey • Property boundaries to be marked – Mapping • Timber stand boundaries or field limits – Mapping • Village centers, trails or roads for general mapping – Consumer • Quick documentation of field location or conditions - Consumer

  19. Geographic Information Systems • Change to other powerpoint….

  20. Geographic Information Systems • An information system that handles geographic data. • Duhhhhhh!!!

  21. THE NEED FOR GIS • the real world has a lot of spatial data • manipulation, analysis and modeling can be effective and efficiently carried out with a GIS • the neighborhood of the intended purchase of house • the route for fire-fighting vehicles to the fire area • location of historical sites to visit • Military purposes • Surveillance (pro and con) • the earth surface is a limited resource • rational decisions on space utilization • fast and quality information in decision making

  22. Geographic Information Systems • Old School • Map-Overlay analysis • New School • Computer based

  23. DATA MODEL OF RASTER AND VECTOR REAL WORLD 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 GRID RASTER VECTOR

  24. RASTER DATA MODEL • derive from formulation that real world has spatial elements and objects fills those elements • real world is represented with uniform cells • list of cells is a rectangle • cell comprises of triangles, hexagon and higher complexities • a cell reports its own true characteristics • per units cell does not represent an object • an object is represented by a group of cells

  25. Lake River Pond Reality - Hydrography Lake River Pond Reality overlaid with a grid 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 0 = No Water Feature 1 = Water Body 2 = River 0 0 0 0 0 0 0 2 1 1 1 0 0 1 1 2 0 0 2 0 0 0 0 0 0 0 0 0 2 2 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 Resulting raster Creating a Raster

  26. DATA MODEL OF RASTER AND VECTOR REAL WORLD 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 GRID RASTER VECTOR

  27. VECTOR CHARACTERICTIS POINT X LINE POLYGON

  28. RASTER TO VECTOR RIVER CHANGED FROM RASTER TO VECTOR FORMAT RIVER THAT HAS BEEN VECTORISED ORIGINAL RIVER

  29. PRO AND CONS OF RASTER MODEL • pro • raster data is more affordable • simple data structure • very efficient overlay operation • cons • topology relationship difficult to implement • raster data requires large storage • not all world phenomena related directly with raster representation • raster data mainly is obtained from satellite images and scanning

  30. PRO AND CONS OF VECTOR MODEL • pro • more efficient data storage • topological encoding • suitable for most usage and compatible with data • good graphic presentation • cons • overlay operation not efficient • complex data structure

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