Location Based Services:
A Gentle Introduction
Presented to: Computer Science 1001
By Shashi Shekhar
Computer Sc. Faculty
University of Minnesota
May 2nd, 2007
Source: http://www.northwoodssurvival.com/content/navigation_class.jpg
Outline
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Introduction
What are LBS?
How are LBS useful?
How does it work?
What’s special about it?
Where to go next?
Introduction
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Q? watched any of the following movies?
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Batman, Mission Impossible,
Spy Kids 2: The Island of Lost Dreams
Minority Report
GPS
…
Ex. What LBS are featured in these movies?
GPS – The Movie
A group of adventure seeking college kids
embark on a GPS treasure hunt in the
Northwest wilderness.
http://www.gpsthemovie.com/
LBS - Examples
• Q? Have we used the following ?
– E.g.: MapQuest, Google Maps, …
– Q? Are these location-based services ?
Courtesy: Microsoft Live Search (http://maps.live.com)
Navigation Devices
• Cell-phone, watch, custom
• For in-vehicle or portable use
Outline
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Introduction
What are LBS?
How are LBS useful?
How does it work?
What’s special about it?
Where to go next?
Source:www.gamma-project.info/images/lbs.jpg
What is LBS? - Wikipedia Perspective
What are LBS?
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Cell-phone-centric definition
– a way to send custom advertising and other information to cell-phone
subscribers based on their current location (Wikipedia)
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Generalized definition
– Service customized to given locations
– It begs 3 questions!
1. Which Location?
– Individual’s current location
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Or favorite locations, e.g. home, work, …
Or Specified location, e.g. a travel destination
– Group of individuals and their locations (?)
2. What implicit spatial relationship to given location?
– Identify service instances near given location(s)
– Neither far nor near given location(s)
3. Which Service?
Outline
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Introduction
What are LBS?
How are LBS useful?
How does it work?
What’s special about it?
Where to go next?
Suspenseful, terrifying, full-length film about a 30'
trimaran's capsize due to poor seamanship in a big
storm while on its way from Vancouver, Canada to
Costa Rica. The 74-day survival efforts … Based on a
true story. (Source: www.multihullsmag.com)
Outline
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Introduction
What are LBS?
How are LBS useful?
How does it work?
What’s special about it?
Where to go next?
Measuring motion and deformation of Earth
Source: wwwrses.anu.edu.au/~anya/polenet/science_gps.htm
Source:www.where2getit.com/products/
How are LBSs useful?
• Numerous Applications
• Emergency Service
– Public Safety – E911, Crime Mapping
– Security – Reverse 911, Evacuation Routes
• Information Services
– Location-based Search – nearest facility
– Routing, Navigation – commuters, travellers
?Future?
• Social Networks
– Location-based friend search
– Smart mobs
• Commerce
– Location based billing, content-push, …
– Asset tracking, Facilities Management
• Science
– Tracking animal habitat, migration, …
GPS Collar, Implantable GPS chip
Sources: www-research.ge.ucl.ac.uk/bear/htm/prtns/va.html ,
www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=360842
Business Applications
• Business Questions
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Predicting consumer spatial behaviors
Delineating trade / service areas
Analyzing market performance by regions
Locating retail and service facilities
• Huff model [1963] : utility = f ( square footage / distance )
Source: http://people.hofstra.edu/geotrans/eng/ch7en/meth7en/hufflaw.html
Location Based Patterns and Scientific Discoveries
• The 1854 Asiatic Cholera in London
– Precursor to germ theory
Location based service in Public Health
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Sample Local Questions from Epidemiology [TerraSeer]
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What’s overall pattern of colorectal cancer
Is there clustering of high colorectal cancer incidence anywhere in the study area
Where is colorectal cancer risk significantly elevated
Where are zones of rapid change in colorectal cancer incidence
Geographic distribution of male colorectal cancer in Long Island, New York (Courtesy: TerraSeer)
Critical locations in Climatology
• Teleconnection
– Find (land location, ocean location) pairs with correlated climate changes
• Ex. El Nino affects climate at many land locations
– Precursor to global warming theories
Average Monthly Temperature
(Courtsey: NASA, Prof. V. Kumar)
Global Influence of El Nino during
the Northern Hemisphere Winter
(D: Dry, W: Warm, R: Rainfall)
Location brings context and aids understanding!
• Location helps bring rich contexts
– Physical: e.g., rainfall, temperature, and wind
– Demographical: e.g., age group, gender, and income type
– Problem-specific, e.g. distance to highway or water
• Understanding of a physical phenomenon
– Though, final model may not involve location
• Cause-effect e.g. Cholera caused by germs
– Discovery of model may be aided by spatial patterns
• Many phenomenon are embedded in space and time
• Ex. 1854 London – Cholera deaths clustered around a water pump
• Spatio-temporal process of disease spread
– => narrow down potential causes
• Ex. Recent analysis of SARS
Technology Risks
Source: http://archive.salon.com/comics/tomo/2001/07/09/tomo/index.html,
www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=360842
Outline
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Introduction
What are LBS?
How are LBS useful?
How does it work?
What’s special about it?
Where to go next?
Navstar ii GPS Satellite
Navigation System using Timing And Ranging
(Source: www.spacetoday.org/Satellites/GPS.htm)l
How does GPS work?
• GPS Receiver
– listens to 3 or more satellites
– Uses triangulation algorithm
– To estimate position
• Challenges
– Multi-path reflections
– Obstructions
• overbridges, skyscrapers
– Leads to errors
– Typical accuracy
• Basic GPS - Few meters
• Differential GPS – sub-meter
Source: GPS Explained
www.kowoma.de/en/gps/positioning.htm
How does it work?
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How does GPS determine locations ?
How does LBS software work ?
What if need more sophisticated spatial reasoning ?
How does LBS Software work ?
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Buy or Build?
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Reusable Libraries are becoming available
Open standards emerging
Ex. Open Location Services – Core Services
1. Directory Service
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online directory (e.g., Yellow Pages) to find the location of a specific or nearest
place, product or service.
2. Gateway Service
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fetches the position of a known mobile terminal
3. Location Utility Service provides
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Geocoder : place name  coordinates
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Example: Street address  (latitude and longitude)
Reverse Geo-coder: coordinates  place name
4. Presentation Service portrays a map
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a base map derived from any geospatial data
and a set of Abstract Data Types as overlays
5. Route Service
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determines travel routes and navigation information between two or more places
Standards: OGC
• What if my application needs more spatial sophistication?
– Ex. Reasoning with extended geographic features
– Q? List restaurants in Minneapolis near rivers or lakes.
• Open GIS Consortium – Simple Features Model
– Basic spatial data types: e.g. point, line, polygons
– Several spatial operations on these spatial data types
Operator Type
Operator Name
Basic Function
SpatialReference, Envelope, Boundary,
Export, IsEmpty, IsSimple
Topological/Set Operations
Equal, Disjoint, Intersect, Touch,
Cross, Within, Contains, Overlap
Spatial Analysis
Distance, Buffer, ConvexHull,
Intersection, Union, Difference,
SymmDiff
Examples of Spatial Operations in OGC Model
Mashups: Location Based Web-Services
Mashups: Location Based Web-Services
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Simple APIs
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Google Earth – KML
Microsoft Virtual Earth SDK
Example Code: KML (Source:http://www.econym.demon.co.uk/googlemaps/kml.htm)
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://earth.google.com/kml/2.0">
<Document>
<name>KML Example file</name>
<description>Simple markers</description>
<Placemark>
<name>Marker 1</name>
<description>Some stuff to put in the first info window</description>
<Point>
<coordinates>-122.1,37.4,0</coordinates>
</Point>
</Placemark>
</Document>
</kml>
What is special about LBS?
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Introduction
What are LBS?
How are LBSs useful?
How does it work?
What’s special about it?
Where to go next?
Source:http://ssnds.uwo.ca/sscnetworkupdate/2006winter/images/gis.jpg
Data in Location Based Services
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Non-spatial Information
– Same as data in traditional data mining
– Numerical, categorical, ordinal, boolean, etc
– e.g., city name, city population
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Spatial Information
– Spatial attribute: geographically referenced
• Neighborhood and extent
• Location, e.g., longitude, latitude,
elevation
– Spatial data representations
• Raster: gridded space
• Vector: point, line, polygon
• Graph: node, edge, path
Raster Data for UMN Campus
Courtesy: UMN
Vector Data for UMN Campus
Courtesy: MapQuest
Spatial Relationships
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Relationships Categories
– Set-oriented: union, intersection, membership, etc
– Topological: meet, within, overlap, etc
– Directional: North, NE, left, above, behind, etc
– Metric: e.g., Euclidean: distance, area, perimeter
– Graph-based: shortest path
– Shape-based and visibility
– …
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Granularity
Granularity
Elevation Example
Road Example
Local
Elevation
On_road?
Focal
Slope
Adjacent_to_road?
Zonal
Highest elevation in a
zone
Distance to nearest road
Mathematical Foundations – Topological Operations
• Topology
– 9-intersections using
• Interior
• boundary
• exterior
 ( Ao  B o ) ( Ao  B) ( Ao  B  ) 
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o

 (A  B ) (A  B) (A  B ) 
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 ( A  B o ) ( A  B) ( A  B  ) 
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Topological
Relationship
9-intersection
model
disjoint
meet
overlap
equal
 0 0 1
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 0 0 1
1 1 1 

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 0 0 1

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 0 11 
1 1 1 
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1 1 1
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1 1 1
1 1 1
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1 0 0 
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0 1 0
 0 0 1
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Q? Define 9-intersection for following operations: inside.
Spatial Autocorrelation (SA)
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First Law of Geography
– “All things are related, but nearby things are more related than distant things.
[Tobler, 1970]”
Pixel property with independent identical
distribution
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Vegetation Durability with SA
Spatial autocorrelation
– Nearby things are more similar than distant things
– Traditional i.i.d. assumption is not valid
– Measures: K-function, Moran’s I, Variogram, …
Location Prediction – Spatial Statistics vs. Classical Statistics!
Nest Locations
Water Depth
Vegetation
Distance to Open Water
Spatial Discontinuities may be anamolous
• Spatial Outliers
– Traffic Data in Twin Cities
– Abnormal Sensor Detections
– Spatial and Temporal Outliers
What is special about LBS?
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Introduction
What are LBS?
How are LBSs useful?
How does it work?
What’s special about it?
Where to go next?
Source: http://qcpages.qc.cuny.edu/career/Career/pictures/assessments/newRoadmap5.jpg
Where to go next?
• Books
• Courses at the U
• Web-sites
– www.spatial.cs.umn.edu
– www.geog.umn.edu/umucgis/
– www.opengis.org
Spatial Thinking Across Disciplines
Courses at U of M