Vector Data Model
This chapter explores the fundamental geometric objects in vector data models, including points, lines, and areas. It explains their dimensional properties, such as the zero dimension of points (location), the one-dimensional nature of lines (length), and the two-dimensional aspects of areas (boundaries and surfaces). The chapter covers map scale ratios, topological data structures, and higher-level objects like triangulated irregular networks and regions. Key concepts of spatial accuracy and topology are also discussed, providing insight into the organization and representation of spatial data.
Vector Data Model
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Presentation Transcript
Vector Data Model Chapter 3
Geometric Objects • What does the object represent? • Point=0 dimension, property of location • Line=1 dimensional and has the property of length • Area=2 dimensional and has the properties of area and boundary. • Basic unit is the point and it’s coordiantes
Line • Line is a series of points. • Node • Vertex • Smooth line • Straight line
Area • Defined by lines • Contiguous areas • Isolated • Overlapped • Hole
Map Scale • Ratio of map distance to ground distance. • 1:24,000 is 1 cm = 24,000 centimeters or 240 meters. • More details on 1:24,000 than on 1:100,000 • What is the symbology?
Topological Data Structure • Point: id, x, y • Line: Arc-node list, Arc-coordinate list • Arc-node list: Arc#, Fnode, Tnode (direction) • Arc-coordinate list: Arc#, x-y coordinates. • Polygon: Left/Right list, Polygon/Arc list • Left/Right list: Arc#, Lpoly, Rpoly • Polygon/Arc list: Polygon#, Arc#
Digitization • Digitizer • Undershoot • Overshoot • Build/Clean (create topology)
Non-topological Vector Data • Computer Aided Design (CAD) • .dxf or .dgn etc • Shapefile (ArcView • .shp = spatial data (geometry) • .shx = index for the .shp • .dbf = attribute data
Higher-Level Objects • Triangulated irregular network (TIN) • Delaunay triangulation – iterative process of connecting points with their two nearest neighbors to form triangles as equiangular as possible. • x, y, and z values (derived slope and aspect) • Sample points • Triangle#, number of adjacent, plus points, lines and attribute data
Higher-Level Objects • Regions • Simple lines and areas • Region layers (regions with same attributes) and regions • Overlap and/or disconnected/disjoint • Subclass of polygon coverage. • Region-polygon list: Region#, Polygon# • Region-arc list: Region#, Ring#, Arc#
Higher-Level Objects • Dynamic Segmentation • Sections: arcs of a line coverage • Routes: collection of selections that represent linear phenomena • Events: attributes connected with dynamic segmentation • Section Table, Route Table, Point Event Table, Linear Event Table (more in ArcView presentation)
Object-Oriented Data Model • Structural Aspects of Objects • Grouping: association, aggregation, generalization, instantiation, and specialization • Behavioral Aspects of Objects • Inheritance, encapsulation, polymorphism.
Spatial Data Concepts • Map scale • Spatial resolution (instrumentation) • Spatial data accuracy • Location accuracy • Precision
Topology • Arc/Info • Connectivity: Arcs connect to each other at nodes • Area definition: An area is defined by a series of connected arcs • Contiguity: Arcs have directions and left and right polygons. • Similar to TIGER
