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Lecture 05: Spatial Data Structure for Computer Cartography

Lecture 05: Spatial Data Structure for Computer Cartography. Geography 128 Analytical and Computer Cartography Spring 2007 Department of Geography University of California, Santa Barbara.

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Lecture 05: Spatial Data Structure for Computer Cartography

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  1. Lecture 05: Spatial Data Structure for Computer Cartography Geography 128 Analytical and Computer Cartography Spring 2007 Department of Geography University of California, Santa Barbara

  2. SDTS is “a robust way of transferring earth-referenced spatial data between dissimilar computer systems with the potential for no information loss. It is a transfer standard that embraces the philosophy of self-contained transfers, i.e. spatial data, attribute, geo-referencing, data quality report, data dictionary, and other supporting metadata all included in the transfer” (USGS, http://mcmcweb.er.usgs.gov/sdts/) Draft standard published in The American Cartographer (1988) FIPS (Federal Information Processing Standards) 173 approved 1992 Standard consists of several parts Spatial Data Transfer Standard(SDTS)

  3. Part 1 - Logical Specifications explain the SDTS conceptual model and SDTS spatial object types, components of a data quality report, and the layout of all SDTS modules Part 2 - Spatial Features contains a catalogue of spatial features and associated attributes Part 3 - ISO 8211 Encoding explains the use of a general purpose file exchange standard, ISO 8211, to create SDTS filesets (i.e. transfers) Part 4 - Topological Vector Profile (SDTS-TVP, e.g., SDTS-DLG) defines how the SDTS base specification (Parts 1, 2, and 3) must be implemented for a particular type of data Spatial Data Transfer Standard(SDTS) (USGS, http://mcmcweb.er.usgs.gov/sdts/)

  4. Part 5 - Raster Profile (SDTS-RP, e.g., SDTS-DEM) for 2-dimensional image and gridded raster data. It permits alternate image file formats using the ISO Basic Image Interchange Format (BIIF) or Georeferenced Tagged information File Format (GeoTIFF) Part 6 - Point Profile (SDTS-PP) contains specifications for use with geographic point data only, with the option to carry high precision coordinates such as those required for geodetic network control points Part 7--Computer Aided Design and Drafting Profile(SDTS-CADDP) contains specifications for an SDTS profile for use with vector-based geographic data as represented in CADD software Spatial Data Transfer Standard(SDTS) (USGS, http://mcmcweb.er.usgs.gov/sdts/)

  5. Data Model maps onto a data structure Data structure eventually implies programming structure Unstructured computer programming languages did not support data structures well Structured languages (e.g. C, Pascal) allow definition of structures directly (attributes only) Data Structures and Programming • Object-oriented languages (e.g. C++, Java) allow definition of objects (attributes + behaviors) • Link between the physical storage of data and the data's use in mapping systems

  6. Most primitive object is the POINT Can be (x,y) or (x,y,z) Consists of geocodes for location in a standard system Zero Dimensional Objects • Should be in world not image geometry • If significant topologically, is a node. • Can identify a feature (entity) or a label (label) • Can be INSIDE an area and carry its identification information

  7. Divide up by lines with and without topological significance Primitive object is the segment Segments connect to make a string (line or polyline) If defined mathematically, use arc If line segment connects nodes, called a link (for a network) Topological versions carry end node and or left and right polygon data Complete, area and network chain versions Area-like objects are G-ring and GT-ring One Dimensional Objects

  8. One Dimensional Objects

  9. Interior area is the space contained by the polygon, i.e. the object not the boundary G-polygon contains graphical objects that form a polygon, e.g. a ring GT-polygon contains complete topology Two Dimensional Objects • Toplogical encoding requires universe and void polygons. • Special objects • pixel (the smallest non-divisible element of a digital image) • Grid cell (same as pixel but for a grid)

  10. DIGITAL IMAGE two dimensional array of regular pixels Aggregate Objects

  11. GRID Set of grid cells forming a regular or near regular tesselation Aggregate Objects (cnt.)

  12. LAYER Distributed set of spatial data representing entity instances within on theme, or with a common attribute. Usually registered with other layers. Aggregate Objects (cnt.)

  13. RASTER One or more overlapping layers from the same grid or digital image. Red Green Blue Aggregate Objects (cnt.)

  14. GRAPH Planar Graph: Node and link/chain set as applied to a plane surface Two-dimensional Manifold: Planar graph with all included objects Network A graph without two-dimensional objects (links do not have to intersect) Limitations Three dimensional objects time-sensitive objects Links to other standards Implementation slow via profiles Aggregate Objects (cnt.)

  15. Map Data Structure Next Lecture

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