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Geodatabases

Geodatabases. by Shawn J. Dorsch. Spatial Databases Part 2. Topics. Definitions Spatial Database vs. Geodatabase Reference Systems Types of Data Spatial Query Processing. Definitions.

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Geodatabases

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  1. Geodatabases by Shawn J. Dorsch

  2. Spatial Databases Part 2

  3. Topics • Definitions • Spatial Database vs. Geodatabase • Reference Systems • Types of Data • Spatial Query Processing

  4. Definitions • Spatial Database – a database that models space, objects in space, or a combination of both. – (Reainthong 3) • Geodatabase – a specialized spatial database that deals specifically with geographical data.

  5. What’s the difference? • A spatial database is used to store a model of any objects within a space. • Might store the components and layout of a circuit board • A geodatabase will hold data within the reference of the world. • Coordinates of a city, boundary of a state, or shape of a river

  6. Spatial Reference System • A projection of the real world into a dataset that defines how spatial data is related. • World Geodetic System (WGS84) – one of the most used geographical reference systems. • The Earth is a sphere so it cannot be projected with 100% accuracy. • http://spatialreference.org/

  7. GIS and Geodatabases • GIS is software that allows the data to be visualized and analyzed. • Search, perform calculations, analyze results, and view statistics • Geodatabases are one means by which GIS can store and query the data. • Also flat data files or geo-raster files.

  8. Types of Data • Traditional data • Non-geographical data • Feature data • Data stored as points, lines, and areas • Raster data • Imagery data that is geo-rectified.

  9. Can be stored using a traditional DBMS Processed with standard SQL Traditional Data

  10. An object that stores a geographical representation Uses vector geometry Good for objects with discrete boundaries Streets, rivers, lakes, states Feature Data

  11. Feature Datatypes - (Shekhar and Sanjay 12)

  12. Raster Data • Imagery data • Satellite imagery, Weather maps • Bitmaps, PNGs, JPEGs

  13. How do we query a bitmap? • Need to store geographical reference data • The coordinate system • A reference point or x,y coordinate • typically the upper left or the lower left corner of the raster • A cell size • The count of rows and columns

  14. How do we query a bitmap? - (shown in ArcGIS Desktop Help)

  15. Flat file uses process called geotagging Add spatial reference as metadata Store them in a geodatabase 2 methods: Store reference to the image file Store image in the table Storage of Rasters

  16. Spatial Queries • Traditional query • Find all the stores that sell books on databases. • Spatial query • Find all the stores that sell books on databases within 10 miles of zip code 15931.

  17. Spatial Operators • Distance • Equals • Disjoint • Intersects • Touches • Crosses • Overlaps • Contains • Intersects • Length • Area

  18. Single stage query: each tuple has to be accessed at most once. Find all the stores within 10 miles of zip code 15931. Query Processing Stores spatial query Zips

  19. Query Processing • Multi stage query: The tuples are sent thru a series of filter queries where each one reduces the size of the result set. • Each filter get increasingly more complex and more costly. - (shown in Spatial Concepts)

  20. Find all store owners who live within ten miles of their store. Query Processing People 1st Stage 2nd Stage Stores

  21. Indexing • R-Trees – like a B-tree, but for multi dimensional data • Splits data into a set of minimum bounding rectangles • At each level of the tree the rectangles get smaller • Quad-Trees – tree structure, internal nodes have up to 4 children • Regions are recursively split into 4 quadrants that get smaller and smaller

  22. Summary • Geodatabases are a type of spatial database • Data is only meaningful in the context of a reference system • Three types of data • Traditional, feature, and raster • SDBMS runs queries in stages to increase efficiency

  23. Bibliography • Shekhar, Shashi and Chawla, Sanjay. Spatial Databases A Tour. Prentice Hall, 2003 • Shekhar, Shashi and Chawla, Sanjay. “Chapter 2: Spatial Concepts and Data Models.” Slides for Spatial Databases: A Tour. Nov. 27, 2009 <http://www.spatial.cs.umn.edu/Book/slides>. • Güting, Ralf Hartmut. “An Introduction to Spatial Database Systems.” dna.fernuni-hagen. Sept. 1994. Nov. 27, 2009 <http://dna.fernuni-hagen.de/papers/IntroSpatialDBMS.pdf>. • “Welcome to ArcGIS Desktop Help 9.2.“ ArcGIS Desktop Help 9.2. March 15, 2007. Nov. 27, 2009 <http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=welcome>. • “Object Modeling and Geodatabases.” University of Texas at Austin Center for Research in Water Resources. July 23, 1995. Nov. 27, 2009 <http://www.crwr.utexas.edu/giswr/resources/library/ch01.pdf>. • “Spatial Concepts.” Oracle® Spatial User's Guide and Reference. Nov. 27, 2009 <http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14255/sdo_intro.htm#BAJDIHJF>. • Reainthong, Tyler. “Spatial Database Systems.” CSE 5330/7330 Fall 2009 FILE ORGANIZATION AND DATABASE MANAGEMENT. Nov. 27, 2009 <http://www.lyle.smu.edu/~mhd/7330f09/reainthong.pptx>.

  24. Questions? • Email me at: sdorsch@mail.smu.edu

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