Geographic Information Systems
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Transcript of Geographic Information Systems
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Geographic Geographic Information SystemsInformation Systems
Spatial Data Models and their Spatial Data Models and their ImplementationImplementation
Komal KapoorAjit Padukone
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AgendaAgenda• Spatial Data Models• Types of Spatial Data Models• Object Models
• Types• Implementation• Operations
• Field Models• Operations – Map Algebra• Raster Representation
• Surface Models• Raster-based• Vector-based
• GIS Libraries
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Models - What are theyModels - What are they• A model is an artificial construction in which parts of a
source domain are represented in a target domain.
• The purpose of the model is to simplify and abstract away from the source domain.
source: GIS: A Computing Perspective 2nd Edition, Worboys and Duckham
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Geospatial Information Models - Geospatial Information Models - TypesTypes1) Object Models
2) Field Models
3) Surface Models
source: Data Models in Commercial GIS Systems, Eric Hoel
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1) Spaghetti Model
Simplest of the Object based data models.
Geometric Representations do not have any explicit relationships.
source: Data Models in Commercial GIS Systems, Eric Hoel
Spaghetti Model of Hurricane Data
source: http://www.snowbirdnationals.com/weather.htm
Object Models - TypesObject Models - Types
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2) Network Model
One-dimensional collection of interconnected Point (Junctions) and Line (Edges) features. Facilitate modelling of constrained flow along edges and through junctions.
source: Data Models in Commercial GIS Systems, Eric Hoel
Object Models - TypesObject Models - Types
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A) Directed Network Models : Hydrological Networks
source: www.riversystems.washington.edu/story/Amazon
Object Models - TypesObject Models - Types
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B) Undirected Network Models: Transport Networks
source: Assessing Spatial Aspects of School Location- Allocation in Copenhagen, Lasse Møller-Jensen
Object Models - TypesObject Models - Types
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Object Models - TypesObject Models - Types3) Topological Model
Controls the Geometric relationships between features and maintain the geometric integrity.Represented in the form of Nodes, Arcs and Faces with explicit relationships between each other.
source: Data Models in Commercial GIS Systems, Eric Hoel
source: http://spatialnews.geocomm.com/features/laserscan2/
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The Open Geospatial Consortium, Inc.® (OGC) leads the development of standards for geospatial and location based services.
The Simple Features Access Specifications define a standard Structured Query Language (SQL) schema that supports storage, retrieval, query and update of feature collections.
The OGC Specifications define a data model for the spatial data. The basic primitives are Point, Curve and Surface. Also are defined other useful structures like MultiPoint, MultiLine, MultiPolygon, etc
source: OpenGIS Implementation Specification for Geographic information - Simple feature access
Object Models - Object Models - ImplementationImplementation
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Object Models - Object Models - ImplementationImplementation
Geometry Class Hierarchy
source: OpenGIS Implementation Specification for Geographic information - Simple feature access
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Operations Spaghetti Models Network Models Topological
ModelsOGC Geometry
Model
equals Yes No Yes Yes
subset of Yes No Yes Yes
is empty Yes No Yes Yes
member of Yes No Yes Yes
disjoint from No No Yes Yes
intersection Yes No Yes Yes
union Yes No Yes Yes
difference No No Yes Yes
Set Oriented Operations
Object Models - OperationsObject Models - Operations
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Object Models - OperationsObject Models - OperationsTopological Operations
Operations Spaghetti Models Network Models Topological
ModelsOGC Geometry
Modelboundary Yes No Yes Yes
interior No No Yes Yes
closure No No Yes Yes
meets Yes No Yes Yes
overlaps No No Yes Yes
is inside No No Yes Yes
covers No No Yes Yes
connected No No Yes Yes
components Yes No Yes Yes
extremes No No Yes Yes
is within No No Yes Yes
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Object Models - OperationsObject Models - OperationsEuclidean Operations
Operations Spaghetti Models Network Models Topological
ModelsOGC Geometry
Model
distance No Yes Yes Yes
bearning/angle No No Yes Yes
length No No Yes Yes
area No No Yes yes
perimeter Yes No Yes Yes
centroid No No Yes Yes
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• Represent spatial variations of an attribute over a set of
locations (spatial framework or support).
• Spatial framework comprise tessellations which can be
regular or irregular.
Regular tessellations Irregular tessellations : TIN
Field Based ModelsField Based Models
Souce : http://geosciences.tamuk.edu/~yu/web/L5312/lecture6.pdf
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TIN GRID
Advantages
•ability to describe the surface at different level of resolution•efficiency in storing data
•easy to store and manipulate•easy integration with raster databases
Disadvantages
•in many cases require visual inspection and manual control of the network
•inability to use various grid sizes to reflect areas of different complexity of relief.
ComparisonComparison of GRID and of GRID and TINTIN
Souce: http://www.ian-ko.com/resources/triangulated_irregular_network.htm
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• Local o trigonometric, exponential, reclassification, selection, and statistical functionso E.g. mapping distances to categories ‘very close’, ‘close’, ‘far’, ‘very far’ (reclassification)o Syntax : sin(c:\data\inraster1)
• Focal o Neighborhood operations : majority, maximum, sum, range, slope calculation etc.o Types of Neighborhoods :o Syntax : focalsum([inlayer1], rectangle, 3, 3)
• Zonalo computing zonal statistics such as sum, mean, maximum etc.o Use for calculation of raster areaso Syntax : zonalmean([inlayer1], c:\spatial\inraster2)
• Globalo generation of Euclidean and cost distance metricso Syntax : eucdistance(e:\data2\inrastersource)
• Overlayso Uses multiple fields e.g. densityo Syntax: mean([inlayer1], [inlayer2], [inlayer3])
Map AlgebraMap Algebra
Souce: ArchGIS 9.2 Desktop Help
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• Space is defined using equally sized cells arranged in rows and
columns
• Can comprise of single or multiple bands
Source: ArchGIS 9.2 Desktop Help
Each band represents a segment of the electromagnetic spectrum collected by a sensor.
Raster Data Raster Data RepresentationRepresentation
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• MrSIDA compression technique especially for maintaining the quality of large images. Allows for a high-compression ratio and fast access to large amounts of data at any scale.
• ESRI GRIDA proprietary ESRI format that supports 32-bit integer and 32-bit floating-point raster grids.
• ERDAS ImagineProduced using IMAGINE image processing software created by ERDAS. IMAGINE files can store both continuous and discrete, single-band and multiband data.
• TIFF(Tagged Image File Format)Widespread use in the desktop publishing world. It serves as an interface to several scanners and graphic arts packages. TIFF supports black-and-white, grayscale, pseudo color, and true color images, all of which can be stored in a compressed or decompressed format.
Examples of RasterExamples of Raster
Souce: ArchGIS 9.2 Desktop Help
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• Possible storage methods for multiple raster data:o store each raster dataset individuallyo mosaic them into one large raster dataseto store them as members of a raster catalog
• Raster catalogs can be used to display adjacent or overlapping raster's without having to mosaic them together into one large file.
• Each raster maintains it own properties: multiple formats, data types, file sizes, and coordinate systems.
Used for storing massive image repositories, retaining overlaps between datasets, managing time series data, and when differences among adjoining images prevent mosaicking.
Source: ArchGIS 9.2 Desktop Help
Raster CatalogsRaster Catalogs
Souce: ArchGIS 9.2 Desktop Help
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• Used to represent the topography of the Earth
• Built using remote sensing data or survey data
• Some applications :oCreating relief mapsoRendering 3D visualizationsoModeling water flowoRectification of aerial photographyoTerrain analyses in geomorphology.
Surface Models Surface Models (Digital Evaluation Models(Digital Evaluation Models))
Souce: Data Models in Commercial GIS Systems, E. Hoel, page 215-219.
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• Raster-based
• E.g. USGS DEM developed by the United States Geological Survey• Digital Terrain Elevation Data (DTED) developed by the National
Imagery and Mapping Agency (NIMA) in support of military applications
Source: http://www.esi.utexas.edu/gk12/workshops/gis/docs/elevation.ppt.
Souce: Data Models in Commercial GIS Systems, E. Hoel, page 215-219.
Surface Models (Contd…)Surface Models (Contd…)
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• Vector-basedo TINs are used to partition the geographic space
• Advantages of TIN
• Facilitates a very close approximation of the surface
• Input vector data is incorporated directly in the model which can be queried as well.
• Preserves proximity based connectivity. Hence interpolation neighborhoods are always comprised of the closest input data/samples.
Source:http://www.geog.ucsb.edu/~good/papers/451.pdf
Surface Models (Contd…)Surface Models (Contd…)
Souce: Data Models in Commercial GIS Systems, E. Hoel, page 215-219.
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Raster and Vector ModelsRaster and Vector Models
Inside Channel: Vector Outside Channel: Raster
3D Terrain Modelling
Source: http://www.ce.utexas.edu/stu/tateec
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Raster and Vector ModelsRaster and Vector Models
Source: http://www.ce.utexas.edu/stu/tateec
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GIS LibrariesGIS LibrariesOpen Source GIS libraries providebasic functionality for certain aspects and tasks of GIS Software.
Most of them follow OGC's specifications regarding GIS Data Models and Operations.
Typically used for graphics, GIS format support and conversion, reprojection, computational geometry, topological operations.
Published under the MIT or LGPL licence. ( Can be used for commercial purposes without releasing source code. )
Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler
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GDAL - Geospatial Data Abstraction Library - library to access raster data formats. - presents a single abstraction model for all formats to an application - written in C++ - Data Structures consist of a Dataset and a RasterBand. - Dataset consists Georeferencing data. - RasterBand consists the actual raster data. - Used by : Google Earth Grass GIS
GIS LibrariesGIS Libraries
Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler
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OGR
- part of the GDAL package.- deals with vector data formats like GML, ESRI shapefiles, GRASS and POSTgreSQL.- Data Structures include Layer, Feature and Geometry.- Feature contains the attribute values and reference to feature geometry.
GIS LibrariesGIS Libraries
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JTS / JCS - Java Topological Suite / Java Conflation Suite.
- java libraries for 2D spatial functions.- supports the various spatial analysis methods and topological operations.- JCS is set of interactive tools for conflating and cleaning vector datasets.- used for coverage cleaning, coverage alignment and road network matching.- Projects using JTS : GeoServer, GeoTools, gvSIG, OpenJUMP, uDig.- Ported to C++ as GEOS- Ported to .NET as .NET Topology Suite.
GIS LibrariesGIS Libraries
Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler
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GPSBabel
- cross-platform, free software to transfer routes, tracks, and waypoint data to and from consumer GPS units, and to convert between over a hundred types of GPS data formats.
- useful because GPS data has many proprietary formats.
- used by many collaborators to OpenStreetMap.
- also popular in "Geocaching" communities.
GIS LibrariesGIS Libraries
Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler
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Questions?Questions?