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Geodatabases by Shawn J. Dorsch Spatial Databases Part 2 Topics • • • • • Definitions Spatial Database vs. Geodatabase Reference Systems Types of Data Spatial Query Processing 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. 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 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/ 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. 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. Traditional Data • Can be stored using a traditional DBMS • Processed with standard SQL ID Addr City State Zip 1 123 Main St. Springfield IL 50641 2 554 Fake St. Cresson PA 15963 3 13 Cherry Ln. Altoona PA 15904 Feature Data • An object that stores a geographical representation • Uses vector geometry • Good for objects with discrete boundaries – Streets, rivers, lakes, states ID Addr City State Zip Location 1 123 Main St. Springfield IL 50641 <point> 2 554 Fake St. Cresson PA 15963 <point> 3 13 Cherry Ln. Altoona PA 15904 <point> Feature Datatypes - (Shekhar and Sanjay 12) Raster Data • Imagery data – Satellite imagery, Weather maps – Bitmaps, PNGs, JPEGs 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 How do we query a bitmap? - (shown in ArcGIS Desktop Help) Storage of Rasters • Flat file uses process called geotagging – Add spatial reference as metadata • Store them in a geodatabase – 2 methods: • Store reference to the image file Cell Shape Image Corner … 1 <polygon> 1.jpg <point> … • Store image in the table Cell Shape Image Corner … 1 <polygon> <blob> <point> … 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. Spatial Operators • • • • • • • • • • • Distance Equals Disjoint Intersects Touches Crosses Overlaps Contains Intersects Length Area Query Processing • Single stage query: each tuple has to be accessed at most once. – Find all the stores within 10 miles of zip code 15931. Stores ID StoreName Location 1 Store 1 <point> spatial query Zips Zip Location 15931 <point> 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) Query Processing • Find all store owners who live within ten miles of their store. People ID Name Addr Location 1 John Doe 123 Main St… <point> 1st Stage 2nd Stage Stores ID Name OwnerID Location 100 Books R Us 1 <point> 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 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 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#BAJD IHJF>. 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>. Questions? • Email me at: [email protected]