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Where we are going today…

Where we are going today…. GPS GIS Hey, there are exams next week. Oct. 4 th and 6 th . Powerpoints now online. www.uvm.edu/~jdavis6. Global Positioning Systems. GPS – Knowing Where You Are. Your location can be expressed in many ways:

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Where we are going today…

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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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