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
Object Models - Types
1) Spaghetti Model
Simplest of the Object based data models.
Geometric Representations do not have any explicit relationships.
source: http://www.snowbirdnationals.com/weather.htm
Spaghetti Model of
Hurricane Data
source: Data Models in Commercial GIS Systems, Eric Hoel
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: www.riversystems.washington.edu/story/Amazon
Object Models - Types
B) Undirected Network Models:
Transport Networks
source: Assessing Spatial Aspects of School Location- Allocation in Copenhagen, Lasse MøllerJensen
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: http://spatialnews.geocomm.com/features/laserscan2/
source: Data Models in Commercial GIS Systems, Eric Hoel
Object Models - Implementation
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
Object Models - Operations
Set Oriented Operations
Operations
Spaghetti
Models
Network Models
Topological
Models
OGC 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
Object Models - Operations
Topological Operations
Operations
Spaghetti
Models
Network Models
Topological
Models
OGC Geometry
Model
boundary
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
Object Models - Operations
Euclidean Operations
Operations
Spaghetti
Models
Network Models
Topological
Models
OGC 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
Field Based Models
• 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
Souce : http://geosciences.tamuk.edu/~yu/web/L5312/lecture6.pdf
Irregular tessellations : TIN
Comparison of GRID and TIN
TIN
Advantages
•ability to describe the
surface at different
level of resolution
•efficiency in storing
data
•in many cases require
visual inspection and
Disadvantages manual control of the
network
Souce: http://www.ian-ko.com/resources/triangulated_irregular_network.htm
GRID
•easy to store and
manipulate
•easy integration with
raster databases
•inability to use various
grid sizes to reflect
areas of different
complexity of relief.
Map Algebra
• 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])
Souce: ArchGIS 9.2 Desktop Help
Raster Data Representation
• 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.
Examples of Raster
•
•
•
•
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 floatingpoint 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-andwhite, grayscale, pseudo color, and true color images, all of which can be
stored in a compressed or decompressed format.
Souce: ArchGIS 9.2 Desktop Help
Raster Catalogs
•
•
•
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.
Souce: ArchGIS 9.2 Desktop Help
Source: ArchGIS 9.2 Desktop Help
Surface Models
(Digital Evaluation Models)
•
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.
Souce: Data Models in Commercial GIS Systems, E. Hoel, page 215-219.
Surface Models (Contd…)
• 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…)
• Vector-based
o 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.
Souce: Data Models in Commercial GIS Systems, E. Hoel, page 215-219.
Source:http://www.geog.ucsb.edu/~good/papers/451.pdf
Raster and Vector Models
3D Terrain Modelling
Inside Channel: Vector
Source: http://www.ce.utexas.edu/stu/tateec
Outside Channel: Raster
Raster and Vector Models
Source: http://www.ce.utexas.edu/stu/tateec
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
GIS Libraries
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 :
Grass GIS
Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler
Google Earth
GIS Libraries
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.
Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler
GIS Libraries
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.
Source: Open Source GIS Libraries, Andreas Neumann, Marco Hugentobler
Questions?