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Sources of Spatial Data

Spatial Data Acquisition OBFS RCN Training November 3-7, 2003 Deana D. Pennington, PhD University of New Mexico. Sources of Spatial Data. Online clearinghouses and archives Digitizing and scanning Field collection with GPS. Online Sources. Federal Initiatives Geospatial One Stop

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Sources of Spatial Data

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  1. Spatial Data AcquisitionOBFS RCN TrainingNovember 3-7, 2003Deana D. Pennington, PhDUniversity of New Mexico

  2. Sources of Spatial Data • Online clearinghouses and archives • Digitizing and scanning • Field collection with GPS

  3. Online Sources Federal Initiatives • Geospatial One Stop • National Map

  4. Geospatial One-Stop Geospatial One-Stop: www.geodata.gov • is one of 24 e-government initiatives sponsored by the Federal Office of Management and Budget to enhance government efficiency and improve citizen services. With the support of all levels of government working together, Geospatial One-Stop will:   • Make it easier to access existing geospatial information across the nation • Facilitate sharing of information and planning for future investments in geospatial data • Expand collaborative partnerships to help leverage investments and reduce duplication of data • Work collaboratively to develop and implement standards to facilitate sharing and use of best practices. • All of these activities advance implementation of the National Spatial Data Infrastructure. National Spatial Data Infrastructure (NSDI) website (www.geo-one-stop.gov)

  5. Geospatial One Stop • Administrative and Political Boundaries • Agriculture and Farming • Atmosphere and Climatic • Biology and Ecology • Business and Economic • Cadastral • Cultural, Society, and Demographic • Elevation and Derived Products • Environment and Conservation • Geolgoical and Geophysical • Human Health and Disease • Imagery and Base Maps • Inland Water Resources • Locations and Geodetic Networks • Oceans and Estuaries • Transportation Networks • Utilities and Communication

  6. National Map National Map: http://nationalmap.usgs.gov Coming Soon…

  7. Others • ESRI (Arc products, and links to many other data types) http://www.esri.com/data/index.html • EOS Data Gateway (NASA imagery) http://edcimswww.cr.usgs.gov/pub/imswelcome/ • Federal Geospatial Data Clearinghouse http://www.fgdc.gov/clearinghouse/clearinghouse.html • USGS EROS Data Center http://edcsns17.cr.usgs.gov/EarthExplorer/ • UNESCO global maps http://upo.unesco.org/maps.asp • United Nations Environment Programme http://www.grid.unep.ch/data/index.php • National Climatic Data Center http://www.ncdc.noaa.gov/oa/ncdc.html • Many local and regional data servers…

  8. Digital Elevation Model (DEM) • Digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals. • The USGS produces five different digital elevation products • 7.5-Minute DEM 30- x 30-meter data spacing • 1-Degree DEM 3- x 3-arc-second data spacing • 2 Arc-Second DEM 2- x 2-arc-second data spacing • 15-Minute Alaska DEM 2- x 3-arc-second data spacing • 7.5-Minute Alaska DEM 1- x 2-arc-second data spacing

  9. Digital Line Graph • Summary • Digital representations by points, lines and areas of planimetric information derived from 7.5- and 15-minute 30- by 60-minute and 1:2 million-scale. • Extent of Program • National

  10. Digital Orthophoto Quads • The geographic extent of the digital orthophoto is equivalent to an orthophoto quarter-quadrangle (3.75-minutes of latitude and longitude), • Extent of Coverage • The DOQ coverage area includes the conterminous United States, Alaska, Hawaii, and Puerto Rico.

  11. Land Use/Land Cover • Land use and land cover data provides information: • on urban or built up land, agricultural land, rangeland, forest land, water, wetlands, barren land, tundra, and perennial snow or ice. • Associated maps display information in five data categories: • (1) political units, • (2) hydrologic units, • (3) census county subdivisions, • (4) Federal land ownership, and • (5) State land ownership. • Extent of Program • National

  12. UNESCO Soils

  13. Scanning and Digitizing Legacy Data: Air photos, maps Digitizing: for points, lines, polygons Scanning: for raster image • Problems: • Digitizing: manual labor (tedious) • Scanning: background noise removal and feature identification (if desired) • Both: georegistration • *See handouts for methods description

  14. Field Data Collection with GPS Field Observations Generalization and Abstraction • It is always necessary to abstract and generalize • Proper generalization requires serous thought • The best generalization for one purpose may be wrong for other purposes • Typically complete coverage is only obtained by numerical interpolation • The quality of predicted values depends largely on the number and distribution of data points Abstract and Generalize Forest Area

  15. Geometric Basis: Triangulation • Position is calculated from distance measurements (ranges) to the known location of satellites. • Mathematically we need four satellite ranges to determine exact position. • NEEDED: distances to satellites

  16. Distances Distance=Velocity x Time (e.g. 60 mph x 2 hours = 120 miles) Satellite transmissions => velocity = speed of light = 186,000 miles per second NEEDED: TIME

  17. t0 t0 t0+x t1 t1 t1+x Travel Time Each satellite has a unique “pseudo-random code” => a complex digital signal BUT...

  18. Data logger clocks are not atomic….not as precise (and much less expensive) Errors!!! Clock Errors Satellite clocks are atomic….very precise (and very expensive) Errors corrected by adding one or more satellites; calculate the correction that makes the location on the ground intersect for all known satellite distances…4

  19. GPS Theory Summary • Distance to a satellite is determined by measuring how long a radio signal takes to reach us from that satellite. • To make the measurement we assume that both the satellite and our receiver are generating the same pseudo-random codes at exactly the same time. • By comparing how late the satellite's pseudo-random code appears compared to our receiver's code, we determine how long it took to reach us. • Multiply that travel time by the speed of light and you've got distance. • Distances from 4 satellites are triangulated to calculate the position of the receiver on the surface of the earth.

  20. Other Errors • Atmospheric interference* • Multipathing (bouncing) • Geometry • Others • To correct…add more satellites, positioned more strategically. GPS unit takes care of choosing optimal satellites. • Planning…use Pathfinder Office software to determine times when best satellite coverage for your location

  21. Differential Correction • Works backwards from known location to calculate what travel time should be • Compares with observed travel times for each satellite • Difference = other errors • Apply difference to data logger calculated position • Works within a few hundred kilometers, where similar atmospheric conditions Known location

  22. Other interesting things… • Real-time differential correction for wayfinding • Excellent horizontal accuracy (DGPS) RMS error = 35 cm • Excellent (but slightly less) vertical accuracy RMS error = 55 cm

  23. GPS Lab # 10 • Divide into groups • Play with equipment • Create data dictionaries • Upload dictionary to GPS unit • GPS sidewalks, bushes, buildings, etc. • Download the data from the GPS unit • Differentially correct • Export to GIS shapefile • View in ArcCatalog • Data cleanup and edit

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