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GIS in Water Resources

GIS in Water Resources. Review for Midterm Exam. Latitude and Longitude in North America. Austin: (30 ° N, 98 ° W) Logan: (42 ° N, 112 ° W). 60 N. 30 N. 60 W. 120 W. 90 W. 0 N. Length on Meridians and Parallels. (Lat, Long) = ( f , l ). Length on a Meridian: AB = R e Df

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GIS in Water Resources

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  1. GIS in Water Resources Review for Midterm Exam

  2. Latitude and Longitude in North America Austin: (30°N, 98°W) Logan: (42°N, 112°W) 60 N 30 N 60 W 120 W 90 W 0 N

  3. Length on Meridians and Parallels (Lat, Long) = (f, l) Length on a Meridian: AB = ReDf (same for all latitudes) R Dl D R 30 N C B Re Df 0 N Re Length on a Parallel: CD = R Dl = ReDl Cos f (varies with latitude) A

  4. Example: What is the length of a 1º increment along • on a meridian and on a parallel at 30N, 90W? • Radius of the earth = 6370 km. • Solution: • A 1º angle has first to be converted to radians • p radians = 180 º, so 1º = p/180 = 3.1416/180 = 0.0175 radians • For the meridian, DL = ReDf = 6370 * 0.0175 = 111 km • For the parallel, DL = ReDl Cos f • = 6370 * 0.0175 * Cos 30 • = 96.5 km • Parallels converge as poles are approached

  5. Horizontal Earth Datums • An earth datum is defined by an ellipse and an axis of rotation • NAD27 (North American Datum of 1927) uses the Clarke (1866) ellipsoid on a non geocentric axis of rotation • NAD83 (NAD,1983) uses the GRS80 ellipsoid on a geocentric axis of rotation • WGS84 (World Geodetic System of 1984) uses GRS80, almost the same as NAD83

  6. Vertical Earth Datums • A vertical datum defines elevation, z • NGVD29 (National Geodetic Vertical Datum of 1929) • NAVD88 (North American Vertical Datum of 1988) • takes into account a map of gravity anomalies between the ellipsoid and the geoid

  7. Coordinate System A planar coordinate system is defined by a pair of orthogonal (x,y) axes drawn through an origin Y X Origin (xo,yo) (fo,lo)

  8. Universal Transverse Mercator • Uses the Transverse Mercator projection • Each zone has a Central Meridian(lo), zones are 6° wide, and go from pole to pole • 60 zones cover the earth from East to West • Reference Latitude (fo), is the equator • (Xshift, Yshift) = (xo,yo) = (500000, 0) in the Northern Hemisphere, units are meters

  9. UTM Zone 14 -99° -102° -96° 6° Origin Equator -90 ° -120° -60 °

  10. Defined for a feature dataset in ArcCatalog Coordinate System Projected Geographic X/Y Domain Z Domain M Domain ArcInfo 8 Reference Frames

  11. X/Y Domain (Max X, Max Y) Long integer max value of 231 = 2,147,483,645 (Min X, Min Y) Maximum resolution of a point = Map Units / Precision e.g. map units = meters, precision = 1000, then maximum resolution = 1 meter/1000 = 1 mm on the ground

  12. Network Definition • A network is a set of edges and junctions that are topologically connected to each other.

  13. Edges and Junctions • Simple feature classes: points and lines • Network feature classes: junctions and edges • Edges can be • Simple: one attribute record for a single edge • Complex: one attribute record for several edges in a linear sequence • A single edge cannot be branched No!!

  14. Polylines and Edges

  15. Junctions • Junctions exist at all points where edges join • If necessary they are added during network building (generic junctions) • Junctions can be placed on the interior of an edge e.g. stream gage • Any number of point feature classes can be built into junctions on a single network

  16. Connectivity Table p. 132 of Modeling our World J125 Junction Adjacent Junction and Edge E2 J124 E3 E1 J123 J126 This is the “Logical Network”

  17. Flow to a sink

  18. 32 64 128 16 1 8 4 2 Eight Direction Pour Point Model Water flows in the direction of steepest descent

  19. 32 64 128 16 1 8 4 2 Flow Direction Grid

  20. Stream cell Cell to Cell Grid Network Through the Landscape

  21. 1 1 1 1 1 1 1 1 1 1 1 4 3 3 1 4 3 1 1 3 1 1 2 1 1 12 1 2 1 12 1 1 1 2 16 1 1 2 1 16 2 1 3 6 25 3 6 1 2 25 Contributing Area Grid Drainage area threshold > 5 Cells

  22. Delineation ofStreams and Watersheds on a DEM

  23. 0 0 0 0 0 3 2 0 0 2 0 0 1 0 11 0 0 1 0 15 2 5 0 1 24 Stream Segments

  24. 1 1 2 1 2 3 5 3 3 5 4 4 4 4 4 6 6 6 Stream Segments in a Cell Network 5 5

  25. Watershed Outlet

  26. Watershed Draining to This Outlet

  27. Watershed andDrainage PathsDelineated from 30m DEM Automated method is more consistent than hand delineation

  28. 1000 Cell Threshold Exceeded at Stream Junction 510 989 1504 (>1000)

  29. Subwatersheds for Stream Segments Same Cell Value

  30. Vectorized Streams Linked Using Grid Code to Cell Equivalents Vector Streams Grid Streams

  31. Delineated Subwatersheds and Stream Networks

  32. A Mesh of Triangles Triangle is the only polygon that is always planar in 3-D Lines Surfaces Points

  33. Tin Triangles in 3-D (x3, y3, z3) (x1, y1, z1) (x2, y2, z2) z y Projection in (x,y) plane x

  34. Delauney Triangulation Maximize the minimum interior angle of triangles No point lies within the circumcircle of a triangle Yes No

  35. 13.0 10.0 9.0 5.0 2.0 Flow On a Triangle

  36. Flow On a TIN

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