Geographic Information Systems Spatial Data Models and their Implementation Komal Kapoor Ajit Padukone

Agenda 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

Models - 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

Geospatial Information Models - Types 1) Object Models 2) Field Models 3) Surface Models source: Data Models in Commercial GIS Systems, Eric Hoel

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: Object Models - Types

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 - Types

A) Directed Network Models : Hydrological Networks source: Object Models - Types

B) Undirected Network Models: Transport Networks source: Assessing Spatial Aspects of School Location- Allocation in Copenhagen, Lasse Møller- Jensen Object Models - Types

3) 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:

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 - Implementation

Geometry Class Hierarchy source: OpenGIS Implementation Specification for Geographic information - Simple feature access

Set Oriented Operations Object Models - Operations

Topological Operations

Object Models - Operations Euclidean Operations

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 tessellationsIrregular tessellations : TIN Field Based Models Souce :

TINGRID 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. Comparison of GRID and TIN Souce:

Local o trigonometric, exponential, reclassification, selection, and statistical functions o 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) Zonal o computing zonal statistics such as sum, mean, maximum etc. o Use for calculation of raster areas o Syntax : zonalmean([inlayer1], c:\spatial\inraster2) Global o generation of Euclidean and cost distance metrics o Syntax : eucdistance(e:\data2\inrastersource) Overlays o Uses multiple fields e.g. density o Syntax: mean([inlayer1], [inlayer2], [inlayer3]) Map Algebra Souce: ArchGIS 9.2 Desktop Help

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 Representation

MrSID A 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 GRID A proprietary ESRI format that supports 32-bit integer and 32-bit floating- point raster grids. ERDAS Imagine Produced 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 Raster Souce: ArchGIS 9.2 Desktop Help

Possible storage methods for multiple raster data: o store each raster dataset individually o mosaic them into one large raster dataset o 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 Catalogs Souce: ArchGIS 9.2 Desktop Help

Used to represent the topography of the Earth Built using remote sensing data or survey data Some applications : o Creating relief maps o Rendering 3D visualizations o Modeling water flow o Rectification of aerial photography o Terrain analyses in geomorphology. Surface Models (Digital Evaluation Models ) Souce: Data Models in Commercial GIS Systems, E. Hoel, page

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: Souce: Data Models in Commercial GIS Systems, E. Hoel, page Surface Models (Contd…)

Vector-based o TINs are used to partition the geographic space Advantages of TIN F acilitates 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: Surface Models (Contd…) Souce: Data Models in Commercial GIS Systems, E. Hoel, page

Raster and Vector Models Inside Channel: Vector Outside Channel: Raster 3D Terrain Modelling Source:

Raster and Vector Models Source:

GIS Libraries Open 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

GD AL - 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 Libraries Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler

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 Libraries

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 Libraries Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler

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 Libraries Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler

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