The Input SubsystemBuilding a GIS databaseGIS Data: Primary & Secondary SourcesSlide 4Government data providersThird Party VendorsInput DevicesDigitizing w/ digitizing tabletInput Devices : Small format digitizerDigitizing TabletSlide 11On-screen digitizing w/ PCSelection & Use of DigitizersSlide 14Input devices: ScannersFlatbed scanner & CCDInput devices: Drum scannerRaster, Vector, or both?ConversionsVector  rasterSlide 21Slide 22Reference Frameworks &TransformationsCoordinate transformationsSlide 25Reference Frameworks & TransformationsTranslationScale ChangeRotationMap Preparation & DigitizingDigitizing: RegistrationDigitizing: What to inputDigitizing: How much to inputDigitizing: Inputs & scaleDigitizing Methods of Input: VectorDigitizing Methods of Input: RasterPresence/absence methodCentroid of cell methodDominant type methodPercent occurrence methodNotes on-- Raster Data Input: Remote SensingRaster Data Input: Remote SensingGPS Data InputSecondary DataMetadataSlide 46Pulling it all togetherThe Input SubsystemGEOG 370Instructor: Christine ErlienBuilding a GIS databaseData selection–Quality–Cost –Input methodData acquisitionData transformationGIS Data: Primary & Secondary SourcesPrimary data sources–Created “in house”•Through your own or your team’s field data collection•By transforming data from sources not yet available digitally•For use by the same organization–High level quality control–Often customized for specific project/application–CostlyGIS Data: Primary & Secondary SourcesSecondary data sources–Outside data providers•Government•Third party vendor–Format conversion often requiredGovernment data providersU.S. Census Bureau–TIGERU.S. Geological Survey–Imagery, DEMs, DRGs, DLGsNatural Resource Conservation Service–STATSGO (U.S. General Soil Map)National Oceanic & Atmospheric Agency–Coastal management–Oil & chemical spills–Coral reef conservationThird Party VendorsESRI TeleAtlas Map DatabasesDeLorme Street Atlas & Topo UsaGeoCommunity Data BundlesInput DevicesManual input devices–Digitizing•Transforms information from analog format (e.g., paper, Mylar)  digital format for computer storage & display•Vector data capture •Methods–Digitizing tablet –On screen digitizing using PC–GPS•Vector data capture–Scanners•Vector & raster data capture (depends on scanner type)Digitizing w/ digitizing tablethttp://www.calmit.unl.edu/geog412/Digitizing.pdfInput Devices : Small format digitizerhttp://www.digitizerpro.com/calcomp.htmDigitizing TabletElectronically active table surface–Fine grid of wires acts as a Cartesian coordinate system –Small & large formats availablehttp://www.calmit.unl.edu/geog412/Digitizing.pdfDigitizing TabletPuck–Connected to tablet–Records locations from map–Crosshair  feature locator–Buttons  indicate beginning/ending of lines/polygons, left/right polygonsAlso called “heads-up” digitizingOn-screen digitizing w/ PChttp://www.esri.com/news/arcnews/winter0102articles/epas-clean-water.htmlSelection & Use of DigitizersQualities to be aware of–Repeatability–Linearity–Resolution–Skew–StabilityRepeatability: Precision; expectation that location data recorded for a single location will be same –Good = 0.001 inchLinearity: Measure of digitizer’s ability to be within a specified distance (tolerance) of the correct value as the puck is move over large distance–Common tolerance level: 0.003 in over 60 inSelection & Use of DigitizersResolution: Digitizer’s ability to record increments of space–Smaller value  higher resolution For an existing digitizer:Stability: Tendency of reading to change as digitizer warms upSkew: Do the results produced have the intended shape?–Rectangular coordinates input  rectangular output–Some portions of the tablet can wear outInput devices: ScannersTypes:–Line-following  vector output•Placed on line, moves on small wheels–Requires technician•Distance/time intervals dictate coordinates recorded–Problem when line is complex•Can get confused (convergence/divergence, color contrast)–Flatbed raster output–Drum scanners Automated but edits require user interventionhttp://www.liv.ac.uk/abe/students/photoshop/images/f05_scanner.jpgFlatbed scanner & CCDInexpensive & commonly availableUse CCD (charge-coupled device)Output: raster image–Can be converted to vectorCCDhttp://www.nortekonline.com/eng/Product/Input devices: Drum scannerScans one line at a timeDrum rotates & sensor moves perpendicular to direction of rotationCan take longer maps than flatbedOutput: raster image–Can be converted to vectorFrom Fundamentals of Geographic Information Systems, Demers (2005)Raster, Vector, or both?Does the project necessitate raster or vector GIS?Is the system you’ll be using capable of converting back & forth?–Most commercial programs are–Need to be aware of the decision rules associated with conversion–Might want to testConversionsVector  raster “rasterization”–Results good visually–Can be problematic for attribution•Edges & raster decision rules (“last come, last coded”)Raster  vector “vectorization”–Blocky-looking–Preserves majority of attribute dataVector  rasterhttp://www.yale.edu/gis/serv_r2v.htmRaster  VectorReference Frameworks &TransformationsDigitizing–Records Cartesian coordinates–Providing projection & zone allows later transformation back to projection–Inverse map projection: 2-D map projection coord. Decimal Degrees (3-D)From Fundamentals of Geographic Information Systems, Demers (2005)Coordinate transformationsInput OutputCoordinate transformationshttp://www.progonos.com/furuti/MapProj/Normal/CartHow/cartHow.htmlReference Frameworks & TransformationsPrimary processes for manipulating graphics–Translation–Scale change–RotationWith these types of graphical manipulation  all necessary transformationsTranslationRelocation of origin on Cartesian surface (X, Y offset values)From Fundamentals of Geographic Information Systems, Demers (2005)Scale ChangeFrom Fundamentals of Geographic Information Systems, Demers (2005)X & Y coordinates are multiplied by a scale factorRotationFrom Fundamentals of Geographic Information Systems, Demers (2005)Angular displacementUsed in projection & inverse projection processesMap