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

3. Global Positioning Systems

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

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

8. GPS Constellation

9. GPS Navigation

13. GPS Satellite Signals

14. 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. 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. Selective Availability is now turned off. Best uncorrected horizontal position today is +/- 30 meters.

15. Pseudo-Range Navigation

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

17. Dilution of Precision (DOP)

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

19. PDOP Effected by Objects

20. Differential Correction

21. Survey-Grade GPS

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

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

24. 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

25. Geographic Information Systems Change to other powerpoint…. Change to other powerpoint….

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

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

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

29. 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

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

31. Pond Lake River Pond Lake River 110 11 111 111 2 2 22 2 2 11 000000000 0000000 00000000 00000000 0000000000 00000000000 Reality - Hydrography Reality overlaid with a grid Resulting raster Creating a Raster 0 = No Water Feature 1 = Water Body 2 = River

32. 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

33. VECTOR CHARACTERICTIS POINTX LINE POLYGON

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

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

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