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Data Management: CoveragesOverview (repeat)PowerPoint PresentationCoverage GenerationConstructing TopologyAdjusting Coverage CoordinatesSlide 8Slide 9Defining the ProjectionSecond ExamplePROJECTDEFINE & PROJECTCOPYProjecting a CoverageSample without a projection file, with input projection defined:Sample without a projection file, with input projection not defined:Projection File - input projection not definedGeoreferencing an ImageDRAWING IMAGESIMAGES SUPPORTEDJoining Adjacent CoveragesAPPENDMAPJOINSlide 23Seamless Merging of Polygon CoveragesSlide 25Merging of Point or Arc CoveragesCOVERAGE OPERATION: DISSOLVEDissolve, pg 2CLIPDENSIFYARCGENERALIZEFUZZY TOLERANCEFUZZY TOLERANCE, pg 201/13/19---UT Dallas POEC 6382 Applied GIS Software1Data Management: Coverages ARC commands for coverage maintenance: creating, maintaining, modifyingGeneration: generateTopology Maintenance: build, cleanCoordinate Adjustment: projectdefine, project, transform, AdjustRegistration: register, rectifyJoining: mapjoin, Append, matchnodeModifying: Dissolve, Clip, densifyarc, generalize01/13/19---UT Dallas POEC 6382 Applied GIS Software2Overview (repeat)•The manipulation of coverages lies at the heart of ArcInfo-based GIS•The methods or commands are numerous and can be classified in many ways•There is always overlap, but basic groupings are –Coverage Query: techniques for querying existing coverages (see query.ppt)–Coverage Maintenance: creating, maintaining and modifying coverages (see covergages.ppt)–Coverage Conversion: converting from one GIS format or data model to another (see convert.ppt)–Spatial Analysis: manipulation of coverages to answer some research question or achieve some operational purpose (see analysis.ppt)•Spatial analysis techniques may be used for coverage query anmd maintenace also• We will discuss Query and Maintenance in the context of Workstation ArcInfo.–query.ppt –coverage.pptArcToolbox includes these in its Data Management component•We will cover the Conversion and Spatial Analysis commands in the context of ArcToolbox, –Conversion.ppt–Analysis.ppt01/13/19---UT Dallas POEC 6382 Applied GIS Software3Coverage Maintenance(in this lecture)•Coverage Generation (ARC)–generate•Topology Maintenance (ARC)–build–clean•Coordinate Adjustment (ARC)–projectdefine–project–transform–Adjust•Registration–register–rectify•Joining coverages (ARC)–mapjoin–append and matchnode•Modifying coverages (ARC)–Dissolve–Clip (also in polygon overlay)–densifyarc–generalize Spatial Analysis Some of the spatial analysis methods, especially polygon overlay, can also be useful for coverage “maintenance”. In essence, you use one coverage to control or effect changes in another. These will be covered in a later lecture. •Polygon Overlay (ARC)–clip–split–erase–update–union –intersect –identityno attribute mergingwith attribute merging01/13/19---UT Dallas POEC 6382 Applied GIS Software4Coverage Generation•You can generate a new coverage from any comma-delimited ascii file that contains a unique identification number (will become the <cover>-id variable, or user-id) and coordinate pairs for points, lines, or polygons.•Prior to creating a coverage, determine if you would like single precision (coordinate accuracy to 3 decimals for geographic decimal degree) or double precision (coordinate accuracy to 6 decimals)•EXAMPLE FOR POINTS:–Arc: precision double–Arc: generate airports–Generate: input airports.gen–Generate: points–Generate: quit–Arc:Remember to build topology after creation of a new coverage–Arc: build airports point01/13/19---UT Dallas POEC 6382 Applied GIS Software5Constructing Topology•BUILD - creates or updates topology and the feature attribute table for a coverage–BUILD <cover> {POLY | LINE | POINT | NODE | ANNO.<subclass>} –build airports point•CLEAN - generates a coverage with correct polygon or arc-node topology. To do this, CLEAN edits and corrects geometric coordinate errors, assembles arcs into polygons and creates feature attribute information for each polygon or arc (i.e., creates a PAT or AAT).–CLEAN <in_cover> {out_cover} {dangle_length} {fuzzy_tolerance} {POLY | LINE}–(See topology in Lecture 1: Arc/INFO Basics)01/13/19---UT Dallas POEC 6382 Applied GIS Software6Adjusting Coverage CoordinatesThere are three basic commands that adjust coverage coordinate values: PROJECT, ADJUST, and TRANSFORM• PROJECT changes the coordinates from one map projection to another. PROJECT is the most mathematically accurate.•ADJUST and TRANSFORM use corrections that you’ve specified through either links or tics. –ADJUST - adjusts or “rubbersheets” a coverage’s features in either direction along the links (control points) in a separate link coverage or file. Links represent the from/to locations used in the adjustment. Adjust will localize coordinate changes.–TRANSFORM - uses tics common to the coverage whose coordinates are to be transformed and an existing coverage to change the coordinates to match the output coverage. Transform scales, skews, rotates, and shifts all coordinates in a coverage but it does not perform ‘rubber sheeting’. Often used to transform a coverage from digitizer units to real-world coordinates.For georeferencing an image, use REGISTER and RECTIFY•REGISTER—interactive application which performs homogeneous transformation for an image•RECTIFY is required after REGISTER to convert the registered image from image coordinates to map coordinates.01/13/19---UT Dallas POEC 6382 Applied GIS Software7•Before you begin you must know: Current Projection of coverageDesired Projection of coverage •FIVE COMPONENTS OF A PROJECTIONCoordinate System US ALBERS, LAMBERTDatum NAD27, NAD83Spheroid CLARK 1866, WGS84, GRS90Units DD, METERS, FEETParameters Depends on Coordinate SystemChanging Projections01/13/19---UT Dallas POEC 6382 Applied GIS Software8Before you can project a coverage/grid or file to a new projection, you must know the current projection.Where would you find this information?•“Describe” the coverage to see if projection shown• Data Source -- metadata• Best Guess--Trial and error Two commands to work with projectionsprojectdefine -- define the projection project - actually projects the coverage from one coordinate system to anotherAfter you project data, do a BUILD on the file.Arc:


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