Location Based Services: A Gentle Introduction

Presented to: Computer Science 1001

By Shashi ShekharComputer Sc. Faculty

University of Minnesota

May 2nd, 2007

Source: http://www.northwoodssurvival.com/content/navigation_class.jpg

Outline• Introduction• What are LBS? • How are LBS useful?• How does it work?• What’s special about it?• Where to go next?

Introduction

• Q? watched any of the following movies?– Batman, Mission Impossible, – Spy Kids 2: The Island of Lost Dreams– Minority Report– GPS – …

• Ex. What LBS are featured in these movies?

GPS – The MovieA 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• 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?• Cell-phone-centric definition

– a way to send custom advertising and other information to cell-phone subscribers based on their current location (Wikipedia)

• Generalized definition – Service customized to given locations– It begs 3 questions!

1. Which Location?– Individual’s current location

• 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• 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• Introduction• What are LBS? • How are LBS useful?• How does it work?• What’s special about it?• Where to go next?

Source:www.where2getit.com/products/Measuring motion and deformation of EarthSource: wwwrses.anu.edu.au/~anya/polenet/science_gps.htm

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

• 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 chipSources: www-research.ge.ucl.ac.uk/bear/htm/prtns/va.html ,

www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=360842

?Future?

Business Applications

• Business Questions– 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

• Sample Local Questions from Epidemiology [TerraSeer]– 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

Global Influence of El Nino during the Northern Hemisphere Winter(D: Dry, W: Warm, R: Rainfall)

Average Monthly Temperature

(Courtsey: NASA, Prof. V. Kumar)

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• 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?• How does GPS determine locations ?

• How does LBS software work ?

• What if need more sophisticated spatial reasoning ?

How does LBS Software work ?

• Buy or Build?– Reusable Libraries are becoming available– Open standards emerging

• Ex. Open Location Services – Core Services

1. Directory Service– online directory (e.g., Yellow Pages) to find the location of a specific or nearest

place, product or service.2. Gateway Service

– fetches the position of a known mobile terminal3. Location Utility Service provides

– Geocoder : place name coordinates• Example: Street address (latitude and longitude)

– Reverse Geo-coder: coordinates place name4. Presentation Service portrays a map

– a base map derived from any geospatial data – and a set of Abstract Data Types as overlays

5. Route Service – 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

• Simple APIs– 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?• 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

• Non-spatial Information– Same as data in traditional data mining– Numerical, categorical, ordinal, boolean, etc– e.g., city name, city population

• 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 CampusCourtesy: UMN

Vector Data for UMN CampusCourtesy: MapQuest

Spatial Relationships

• 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– …

• 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

Topological

Relationship

disjoint meet overlap equal

9-intersection

model

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Q? Define 9-intersection for following operations: inside.

Spatial Autocorrelation (SA)

• First Law of Geography– “All things are related, but nearby things are more related than distant things.

[Tobler, 1970]”

• 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, …

Pixel property with independent identical distribution

Vegetation Durability with SA

Location Prediction – Spatial Statistics vs. Classical Statistics!

Nest Locations Vegetation

Water Depth 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?• 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