Kiến trúc xây dựng - Lecture 3: Gis data models

Lecture 3:GIS Data ModelsAIM: To introduce various GIS data modelsAfter this lecture you should be able to:Describe the primary Vector data models used in GIS and give examplesDescribe raster data models and give examplesDescribe TIN data modelsExplain “topology”Describe the main file formats used in GISGraphic FeaturesObjects which are shown on a map are called graphic features or features. These features may be natural or man made objects.Digital representation of physical or man made elements:Graphic FeaturesVectorsPoints or NodesLines or ArcsPolygonsRaster Cells or PixelsImagesDigital OrthophotographyGeographic Data TypesImagesVectorRaster (GRID)AttributesTIN (Triangulated Irregular Network)Annotation© Paul Bolstad, GIS FundamentalsGeographic Data Types© Paul Bolstad, GIS FundamentalsDIGITAL SPATIAL DATA RASTER VECTOR Real WorldSource: Defense Mapping School National Imagery and Mapping AgencyElectronic Maps in Raster and Vector FormatsRaster Data SourcesSatelliteImageryAir PhotosScanned MapsDigital OrthophotographImageCopyright 1993 Nassau County, NYA scanned photograph that has been mathematically rectified to eliminate the effects of displacement so that its view always appears as though it is perpendicular to the ground.Scanned DocumentA set of colored pixels representing chart information as a picture on computer screenSimply an array of pixels arranged in rows and columnsPixels are color coded, but do not represent features explicitlyRasters can have value attachedSource: Defense Mapping School National Imagery and Mapping AgencyRaster Maps (images)The Appeal of Raster Looks like a paper mapCheap and easy to produce (scan existing paper chart)Runs easily on PCWorld-wide availability w/updates availableProblems:Datum may or may not be WGS84Does not allow automated grounding avoidance or any other computer-aided analysisStorage not as efficientSource: Defense Mapping School National Imagery and Mapping AgencyVector DataSource: Defense Mapping School National Imagery and Mapping AgencyAn intelligent form of digital geographic data where real world objects are represented by points, lines and polygons. An objects representation is described by attributes and coordinates.Examples include: Digitized Maps GIS Data In addition to Geography, GIS is also about Information. A GIS marries the capabilities of computer mapping with database management systems. So, a geospatial analyst can “click” on a geographic feature and find out information about it. Or, they can query the database to find out information about all the geographic objects that meet a specific criteria.Information about a geographic object is called an attribute.Linking Attributes and GraphicsLinking Attributes with GraphicsIn this example, the user has issued a query to select all the properties whose classification is single family residential (210), and colored the selection red.Vector Data is LayeredSpatial Data Analysis•••••••••••251476LakeFeatures:LinePoints:ConnectedDetachedAreaText•LakeGeographic data are separatedinto themes, tiled for speed of access and placed on CD-ROMNetwork Analysis30 30’ N040 40’ E30 30’ N040 50’ ESource: Defense Mapping School National Imagery and Mapping AgencyParadigm ShiftMay look “different” from a paper map (software-dependent)Underlying database allows queries and layer selectionZooming reveals detailComplex, expensive, and time-consuming to produceSource: Defense Mapping School National Imagery and Mapping AgencyRaster and Vector Data Models Vector RepresentationX-AXIS500400300200100600500400300200100Y-AXISRiverHouse600 Trees TreesBBBBBBBBGGBKBBBGGGGG Raster Representation1234567891012345678910 Real WorldG G Source: Defense Mapping School National Imagery and Mapping AgencyA GIS in which graphic data is stored in the form of discrete points, lines, or polygons.Vector GIS© Paul Bolstad, GIS FundamentalsStructure of Vector DataThere is a relationship between vector data types. Each data type is often dependent upon one another. When representing geographic data in vector format, data is typically stored as:Points: points are zero dimensional objects, and represent geographic features such as wells, sample locations, or trees.Lines: lines represent one dimensional objects, or linear features, such as road and stream centerlines. Lines are made up of a series of interconnected points. A line typically starts and end with a special point called a node, and the points that make up the rest of a line are called vertices. Polygons/Area: polygons represent two dimensional objects such as the boundaries of a field, or property, or the outline of a building or lake. Polygons are made up of a series of connected lines where the starting point of a polygon is the same as the ending point. PointLinePolygonPoints are zero dimensional objects which have locations and attribute information but are too small to be represented as areas.PointsPointsSoil SamplesTypePHContaminantsUtility PolesOwnerHeightAttachmentsSpill LocationsAccident NumberType of SpillExtentParcel CentroidsSection/Block/Lot No.AddressOwnerAssessment DataLight PolesParcel CentroidsLines are one dimensional objects which have length but no area.Each line must begin and end at a node.Lines or ArcsLines or ArcsStreet CenterlineStreet NameAddress RangesWater MainPipe sizePipe MaterialDate InstalledStreamDepthQualityFlow RateStreet CenterlinesPolygons are closed mathematical figures of any shape or size. They are formed by a series of connected lines.PolygonsPolygonsParcelParcel ID NumberDimensions and AreaSoil BoundariesTypePermeabilityFlood ZonesPolygonsPolygons“Linked” Attribute DataTabular Data(Attributes)© ESRIInformation which describes an entity represented by a graphic feature. Attribute DataInformation about a graphic featureAttribute DataEach piece of attribute information is related to a specific graphic elementTraditional database type fieldsImagesPhotosVideoCourtesy Village of Garden City“Linked” AttributesA GIS in which graphic data is stored in the form of grid cells or pixels.Part 3: Raster GISRaster DataGeographic Data SetsLand Use/Land CoverVegetation IndexSoil StabilityDigital PhotographyBuilding PhotosAccident ScenesCrop DamageFull Motion VideoDigital OrthophotographyRectified Aerial Photos© ESRI, Modeling Our WorldAbbreviation for PICTURE ELEMENT, which is the smallest unit in an image. In raster based GIS systems, attribute information can be assigned to each pixel.PIXEL© ESRI, Modeling Our World© ESRI, Modeling Our WorldRaster Data StructureMatrix of Equal-Area CellsIssue of ResolutionWHEATHAYAPPLESWHEATHAYAPPLESRaster Vs. VectorMust ConsiderDiscreteness of the entity being depictedIntended application (efficiencies)Source dataStorage considerationsResolutionColorRaster vs. Vector ModelSource: Defense Mapping School National Imagery and Mapping AgencyPeople often ask: “what is the best format to represent geographic objects in a GIS, raster of vector?” The answer is actually neither and both! That is, neither data model is better in every circumstance, and both data models fulfill very specific roles in GIS.In this example, the vector data source representing the shoreline appears to have greater detail, and possibly greater accuracy. Vector data can often store the information in a more compact format than raster data, and also work well with linear objects such as stream networks.However, raster data models are much better at representing information that is continuous in nature, such as temperature where the value of temperature may be different between neighbors.Vector – Advantages and DisadvantagesAdvantagesGood representation of realityCompact data structureTopology can be described in a networkAccurate graphicsDisadvantagesComplex data structuresSimulation may be difficultSome spatial analysis is difficult or impossible to performRaster – Advantages and DisadvantagesAdvantagesSimple data structureEasy overlayVarious kinds of spatial analysisUniform size and shapeCheaper technologyDisadvantagesLarge amount of dataLess “pretty”Projection transformation is difficultDifferent scales between layers can be a nightmareMay lose information due to generalizationRaster Functions© Paul Bolstad, GIS FundamentalsTriangulated Irregular NetworkA triangulated irregular network (TIN) is a data model that is used to represent three dimensional objects. In this case, x,y, and z values represent points. Using methods of computational geometry, the points are connected into what is called a triangulation, forming a network of triangles. The lines of the triangles are called edges, and the interior area is called a face, or facet. While the TIN model is somewhat more complex than the simple point, line, and polygon vector model, or the raster model, it is actually quite useful for representing elevations. For example a raster grid would require grid cells to cover the entire surface of a geographic area. Also, if we wanted to show great detail we would have to have small grid cells. Now, if the land area is relatively flat, we would still need the small grid cells. However, with a TIN we would not have to include so many points on the flat areas, but could add more points on the steep areas where we want to show greater detail.The illustration shows how we can create a TIN of the terrain around Ithaca, NY. TIN Data StructuresThe tin data structure is based on two basic elements: points with x,y,z values, and a series of edges joining these points to form triangles. This triangular mosaic forms a continuous faceted surface, much like a jewel. TIN’s triangulation method satisfies the Delaunay criterionDelaunay CriterionThe triangulation algorithm ensures that the Delauney criterion is satisfied. The Delauney criterion is such that the circumcircle of a triangle does not enclose a node on any other element. The circumcircle of a triangle is the circle that passes through its vertices. Components of a TINNodesEdgesTrianglesHullTopologyTIN is a set of adjacent, non-overlapping triangles computed from irregularly spaced points with x, y coordinates and z values. ArcGIS supports two data models of elevation: TIN and lattice. Components of TIN (in detail)Nodes: nodes are the fundamental building blocks of the tin. The nodes originate from the points and arc vertices contained in the input data sources. Edges: every node is joined with its nearest neighbors by edges to form triangles which satisfy the Delaunay criterion. Each edge has two nodes, but a node may have two or more edges. Triangles: Each triangular facet describes the behavior of a portion of the tin’s surface. Hull: The hull of tin is formed by one or more polygons containing the entire set of data points used to construct the tin. The hull polygons define the zone of interpolation of the tin. Topology: The topological structure of a tin is defined by the relationship between  nodes, edges (number and type), and by the relationship between adjacent triangles. Like an ARC/INFO coverage, a tin is stored as a directory of files. However, a tin is not a coverage and has no associated INFO files. A tin directory contains seven files containing information about the tin surface. These files are encoded in binary format and are not readable by standard text display.  © ESRI, Modeling Our World© ESRI, Modeling Our WorldText or labels plotted on a map which describe or identify a feature or add other information to the map.AnnotationAnnotationTextInformation placed on a map to provide additional information about a graphic feature.SymbolsThe means by which graphic features are displayed in a GIS.Symbols help identify features and provide information about them.q c , P XSymbolsCourtesy Village of Garden CityAnnotation, Symbology, and TextIssues of Scale in Feature RepresentationDepending upon the presentation scale, a feature may take on different formsBuildingsEngineering drawing – building outlineUSGS Quad Sheet – point locationCityUSGS Quad Sheet – Polygon of city boundaryRand McNally Map – Point representing city locationA collection of numeric data which clearly describes adjacency, containment, and connectivity between map features and which can be stored and manipulated by a computer.TopologyTopology© Paul Bolstad, GIS FundamentalsARC/INFO vs. ArcViewARC/INFO is a topologically based hybrid systemArcView is a file based, non topological, pseudo object-oriented graphic data structureFile FormatsARC/INFO CoverageArcView ShapeGeodatabase LayerAutoCAD DWG/DXFMapINFOOtherThe Shape FileThe shapefile format defines the geometry and attributes of geographically-referenced features in as many with specific file extensions that must be stored in the same project workspace. They are:.shp - the file that stores the feature geometry. Required..shx - the file that stores the index of the feature geometry. Required..dbf - the dBASE file that stores the attribute information of features. Required..sbn and .sbx - the files that store the spatial index of the features. Optional.© ESRI, Modeling Our World© ESRI, Modeling Our WorldHomeworkReading: A PDF document on data models Exercise: GTK 5abcd (Symbolizing features and rasters)