Download Geodatabases

Geodatabases
by Shawn J. Dorsch
Spatial Databases Part 2
Topics
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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
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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
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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]