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Vector Data Model

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.

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Vector Data Model

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  1. Vector Data Model Chapter 3

  2. 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

  3. Line • Line is a series of points. • Node • Vertex • Smooth line • Straight line

  4. Area • Defined by lines • Contiguous areas • Isolated • Overlapped • Hole

  5. 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?

  6. 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#

  7. Digitization • Digitizer • Undershoot • Overshoot • Build/Clean (create topology)

  8. 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

  9. 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

  10. 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#

  11. 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)

  12. Object-Oriented Data Model • Structural Aspects of Objects • Grouping: association, aggregation, generalization, instantiation, and specialization • Behavioral Aspects of Objects • Inheritance, encapsulation, polymorphism.

  13. Spatial Data Concepts • Map scale • Spatial resolution (instrumentation) • Spatial data accuracy • Location accuracy • Precision

  14. 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

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