Spatial Data AcquisitionSpatial Data Acquisition

OBFS RCN TrainingOBFS RCN TrainingNovember 3-7, 2003November 3-7, 2003

Deana D. Pennington, PhDDeana D. Pennington, PhDUniversity of New MexicoUniversity of New Mexico

Sources of Spatial DataSources of Spatial Data

Online clearinghouses and Online clearinghouses and archivesarchives

Digitizing and scanning Digitizing and scanning Field collection with GPSField collection with GPS

Online SourcesOnline Sources

Federal Initiatives Federal Initiatives Geospatial One StopGeospatial One Stop

National MapNational Map

Geospatial One-StopGeospatial One-StopGeospatial One-Stop: www.geodata.govGeospatial One-Stop: www.geodata.gov

is one of 24 e-government initiatives sponsored by the Federal Office of is one of 24 e-government initiatives sponsored by the Federal Office of Management and Budget to enhance government efficiency and improve citizen Management and Budget to enhance government efficiency and improve citizen services.services.

With the support of all levels of government working together, Geospatial With the support of all levels of government working together, Geospatial One-Stop will:  One-Stop will:  

Make it easier to access existing geospatial information across the nation Make it easier to access existing geospatial information across the nation Facilitate sharing of information and planning for future investments in Facilitate sharing of information and planning for future investments in

geospatial data geospatial data Expand collaborative partnerships to help leverage investments and reduce Expand collaborative partnerships to help leverage investments and reduce

duplication of data duplication of data Work collaboratively to develop and implement standards to facilitate sharing Work collaboratively to develop and implement standards to facilitate sharing

and use of best practices. and use of best practices. All of these activities advance implementation of the National Spatial Data All of these activities advance implementation of the National Spatial Data

Infrastructure. Infrastructure.

National Spatial Data Infrastructure (NSDI) website (www.geo-one-stop.gov)

Geospatial One StopGeospatial One StopAdministrative and Political BoundariesAgriculture and FarmingAtmosphere and ClimaticBiology and EcologyBusiness and EconomicCadastralCultural, Society, and DemographicElevation and Derived ProductsEnvironment and ConservationGeolgoical and GeophysicalHuman Health and DiseaseImagery and Base MapsInland Water ResourcesLocations and Geodetic NetworksOceans and EstuariesTransportation NetworksUtilities and Communication

National MapNational MapNational Map: http://nationalmap.usgs.govNational Map: http://nationalmap.usgs.gov

ComingSoon…

OthersOthers

ESRI (Arc products, and links to many other data ESRI (Arc products, and links to many other data types) http://www.esri.com/data/index.htmltypes) http://www.esri.com/data/index.html

EOS Data Gateway (NASA imagery) EOS Data Gateway (NASA imagery) http://edcimswww.cr.usgs.gov/pub/imswelcome/http://edcimswww.cr.usgs.gov/pub/imswelcome/

Federal Geospatial Data Clearinghouse Federal Geospatial Data Clearinghouse http://www.fgdc.gov/clearinghouse/clearinghouse.htmlhttp://www.fgdc.gov/clearinghouse/clearinghouse.html

USGS EROS Data Center USGS EROS Data Center http://edcsns17.cr.usgs.gov/EarthExplorer/http://edcsns17.cr.usgs.gov/EarthExplorer/

UNESCO global maps UNESCO global maps http://upo.unesco.org/maps.asphttp://upo.unesco.org/maps.asp

United Nations Environment Programme United Nations Environment Programme http://www.grid.unep.ch/data/index.phphttp://www.grid.unep.ch/data/index.php

National Climatic Data Center National Climatic Data Center http://www.ncdc.noaa.gov/oa/ncdc.htmlhttp://www.ncdc.noaa.gov/oa/ncdc.html

Many local and regional data servers…Many local and regional data servers…

Digital Elevation Model Digital Elevation Model (DEM)(DEM)

Digital file consisting of Digital file consisting of terrain elevations for terrain elevations for ground positions at ground positions at regularly spaced regularly spaced horizontal intervals. horizontal intervals.

The USGS produces five The USGS produces five different digital elevation different digital elevation productsproducts

1.1. 7.5-Minute DEM 7.5-Minute DEM 30- x 30-30- x 30-meter data spacing meter data spacing

2.2. 1-Degree DEM1-Degree DEM 3- x 3-arc- 3- x 3-arc-second data spacing second data spacing

3.3. 2 Arc-Second DEM2 Arc-Second DEM 2- x 2- 2- x 2-arc-second data spacing arc-second data spacing

4.4. 15-Minute Alaska DEM15-Minute Alaska DEM 2- 2- x 3-arc-second data spacing x 3-arc-second data spacing

5.5. 7.5-Minute Alaska DEM7.5-Minute Alaska DEM 1- 1- x 2-arc-second data spacing x 2-arc-second data spacing

Digital Line GraphDigital Line Graph

Summary Summary Digital representations by Digital representations by

points, lines and areas of points, lines and areas of planimetric information planimetric information derived from 7.5- and 15-derived from 7.5- and 15-minute 30- by 60-minute and minute 30- by 60-minute and 1:2 million-scale. 1:2 million-scale.

Extent of Program Extent of Program National National

Digital Orthophoto Digital Orthophoto QuadsQuads

The geographic extent The geographic extent of the digital orthophoto of the digital orthophoto is equivalent to an is equivalent to an orthophoto quarter-orthophoto quarter-quadrangle (3.75-quadrangle (3.75-minutes of latitude and minutes of latitude and longitude), longitude),

Extent of CoverageExtent of Coverage The DOQ coverage area The DOQ coverage area

includes the conterminous includes the conterminous United States, Alaska, United States, Alaska, Hawaii, and Puerto Rico. Hawaii, and Puerto Rico.

Land Use/Land CoverLand Use/Land Cover Land use and land cover data Land use and land cover data

provides information:provides information: on urban or built up land, on urban or built up land,

agricultural land, rangeland, agricultural land, rangeland, forest land, water, wetlands, forest land, water, wetlands, barren land, tundra, and barren land, tundra, and perennial snow or ice. perennial snow or ice.

Associated maps display Associated maps display information in five data information in five data categories: categories: (1) political units, (1) political units, (2) hydrologic units, (2) hydrologic units, (3) census county subdivisions, (3) census county subdivisions, (4) Federal land ownership, and (4) Federal land ownership, and (5) State land ownership. (5) State land ownership.

Extent of Program Extent of Program National National

UNESCO SoilsUNESCO Soils

Scanning and DigitizingScanning and DigitizingLegacy Data: Air photos, mapsLegacy Data: Air photos, maps

Problems:•Digitizing: manual labor (tedious)•Scanning: background noise removal and feature identification (if desired)•Both: georegistration

*See handouts for methods description

Digitizing: for points, lines, polygonsDigitizing: for points, lines, polygons

Scanning: for raster imageScanning: for raster image

Field Data Collection with Field Data Collection with GPSGPS

Generalization and AbstractionGeneralization and Abstraction It is always necessary to abstract and It is always necessary to abstract and

generalizegeneralize Proper generalization requires serous Proper generalization requires serous

thoughtthought The best generalization for one The best generalization for one

purpose may be wrong for other purpose may be wrong for other purposespurposes

Typically complete coverage is only Typically complete coverage is only obtained by numerical interpolationobtained by numerical interpolation

The quality of predicted values The quality of predicted values depends largely on the number and depends largely on the number and distribution of data pointsdistribution of data points

Abstract and Generalize

Abstract and Generalize

Field Observations

Forest Area

Geometric Basis: Geometric Basis: TriangulationTriangulation

•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 

DistancesDistances

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

Travel TimeTravel Time

Each satellite has a unique “pseudo-random code”=> a complex digital signal

t0 t1

t0 t1

t0+x t1+x

Clock ErrorsClock ErrorsSatellite clocks are atomic….very precise (and very expensive)

Data logger clocks are not atomic….not as precise (and much less 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

GPS Theory SummaryGPS 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.

Other ErrorsOther 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

Differential CorrectionDifferential Correction

Known location

1. Works backwards from known location to calculate what travel time should be

2. Compares with observed travel times for each satellite

3. Difference = other errors

4. Apply difference to data logger calculated position

5. Works within a few hundred kilometers, where similar atmospheric conditions

Other interesting Other interesting things…things…

Real-time differential correction for Real-time differential correction for wayfinding wayfinding

Excellent horizontal accuracy Excellent horizontal accuracy (DGPS)(DGPS)

RMS error = 35 cmRMS error = 35 cm

Excellent (but slightly less) vertical Excellent (but slightly less) vertical accuracyaccuracy

RMS error = 55 cmRMS error = 55 cm

GPS Lab # 10GPS Lab # 10

Divide into groupsDivide into groups Play with equipment Play with equipment Create data dictionariesCreate data dictionaries Upload dictionary to GPS unit Upload dictionary to GPS unit GPS sidewalks, bushes, GPS sidewalks, bushes,

buildings, etc.buildings, etc. Download the data from the Download the data from the

GPS unitGPS unit Differentially correctDifferentially correct Export to GIS shapefileExport to GIS shapefile View in ArcCatalogView in ArcCatalog Data cleanup and editData cleanup and edit