10.1 Positioning
10.2 Car Navigation 10.3 Map Matching 10.4 Privacy
10.5 Summary
10 Location Based Services
• Location Based Services (LBS) are services,
– That are accessible with mobile devices through a mobile network
– Integrating a mobile device’s location with other
information so as to provide added value to the user
• Classification of LBS applications
– Person-oriented
• Person located can control the service
– Device-oriented
• Person or object located is not controlling the service
10 Location Based Services
https://www.acid21.com/
• Types of application design
– Pull Services
– Push Services
10 Location Based Services
Event Data transfer
Request Response
• Application examples
10 Location Based Services
Push Services Pull Services Person-
oriented
Communication A message is pushed to you asking whether you allow a friend to locate you
You request from a friend finder application who is near you
Information You get an alert that a terror alarm has been issued by the city you are in
You look for the nearest cinema in your area and navigation instructions to get there M-Commerce
and Advertising
A discount voucher is being sent to you from a restaurant in the area you are in
You look for events happening in the area you are in
Device- oriented
An alert is sent to you from an asset-tracking application that one of your shipments has just deviated from its foreseen route
You request information on where your truck fleet currently is located in the country
• Application areas
– Travel services
• Routing, city, hotel and restaurant guides
– Emergency
• Locating a person in need, warn persons in danger
– Fleet management – Phone tracker
• Child watch, anti-theft tracking
– Friend finder, blind dating – Mobile phone tariffs
10 Location Based Services
http://sourceforge.net/dbimage.php?id=132227
• Self-locating: User (his mobile device) locates himself
– Global Positioning System (GPS, GLONASS, Galileo) – Manual position input (not smart)
• External locating: Operator
locates the user’s mobile device
– Determining the current mobile network cell – Signal comparison between three adjacent cells
• Locating provided by third parties
– Location transponder – Peer-to-Peer locating
10.1 Positioning
http://www.nundenn.de/
• Global Positioning System (GPS)
– Enables three dimensional positioning near the earth – Measuring the runtime of signals between the satellite
and the GPS-receiver, from which the distance and the position can be deduced (trilateration)
– The transmitted signal describes a circular sphere centered at the
satellite on which surface the signal is received at the same
time → circular baseline of equal receiving times
on earth
10.1 Positioning
http://www.uni-giessen.de/ilr/frede/
lehrveranstaltungen/MP_51/2.6-GPS.pdf
– From the intersection of baselines of (at least) three satellites the position on the earths surface is deduced – Prerequisite is the temporal coordination of the
satellites and the receiver, otherwise the baseline of a fourth satellite is needed
10.1 GPS
http://www.uni-giessen.de/.../2.6-GPS.pdf [La13]
• Illustrating the equation for one
satellite
10.1 GPS
– Navigational Satellite Timing and Ranging - Global Positioning System (NAVSTAR-GPS)
• Currently the most important positioning and navigation system worldwide
• Operator: United States Air Force
• 1973: decision on development
• 1978-1985: launch of 11 block I-satellites
• March 1994: launch of the last block II-satellites
• July 1995: full operational capability
• 1.5.2000: enhanced accuracy for civilian users (from approx.
100m to 20m)
10.1 GPS
https://timeandnavigation.si.edu/
– Three major segments: space, control and user segment
– Between 24 and 32 satellites – Six orbits
• 55o inclination each
• 20200 km altitude
• 11 h 55 min orbital period
– From every point at earth at least 5 satellites are always visible
– 5 different types of satellites:
Block I, Block II, Block IIA, Block IIR, and Block IIF
Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 852
10.1 GPS
http://www.iww.forst.uni-goettingen.de/
– Block II satellites
• Weight: 1500 kg
• Span 5.1 m
• Durability 7.5 years
• 2 (IIR 3) rubidium and 2 cesium atomic clocks with a stability of at least 10 - 13 s
• Power source: solar panels 750 watt
• Radiated power 50 watt
• A hydrazine propulsion system for orbital correction
10.1 GPS
http://www.kowoma.de/
gps/Satelliten.htm
IIA IIR
http://www.irs.uni-stuttgart.de/
– Control segment
• Almost passive ground stations to track the flight paths of the satellites
4 monitoring stations operated by the U.S. air force
Since end of 2005 6 more stations operated by the NGA (National Geospatial-Intelligence Agency)
One "Master Control Station" for evaluation
• Every satellite can
always be received
by at least two ground stations
10.1 GPS
http://www.kowoma.de/gps/Bodenstationen.htm
– GPS-receiver
• Composed of an antenna, receiver-processors, and a highly- stable clock
• May also include a display for providing location and speed information
• Dedicated devices or integrated into cars, mobile phones,
watches, etc.
10.1 GPS
http://www.ecvv.com/
http://3.imimg.com/
– Message format
• Week and time within the week
• Position
10.1 GPS
every 6 seconds
http://imaging.utk.edu/publications/papers/dissertation/Anis_Pilot.pdf
• Health of the satellite
• Ephemeris
– In a spherical polar coordinate system – Updated every 2h
• Almanac
– Coarse orbit and status information for all satellites
– Data related to error correction
– Updated every 24h
10.1 GPS
http://www.uni-giessen.de/ilr/frede/
lehrveranstaltungen/MP_51/2.6-GPS.pdf
– Random errors: current local conditions at the location of the receiver
• Dense forests: signal damping
• Mountains, narrow valleys, street canyons: shadowing effects
• Large buildings: multipath effect
• Tall metal construction elements:
echo effect, signal distortion
• Strong transmitters and high-voltage power lines
– Best receiving conditions in the open country with small relief
10.1 GPS
http://www.kowoma.de/en/gps/errors.htm
– Clock errors
• Relativistic effects
– Time moves the faster the weaker the field of gravitation is – Time runs slower during very fast movements
• Inaccuracy of the time of the receiver clock
– Change of speed of propagation of radio waves in the atmosphere
• Ionosphere (80-900 km): electromagnetic waves are slowed down inversely proportional to the square of their frequency
• Troposphere (0-15 km): refraction due to different concentrations of
water vapour
10.1 GPS
http://www.kowoma.de/en/gps/errors.htm
• Differential GPS (DGPS)
10.1 GPS
base or reference station:
set up on a precisely known location calculates its position based on
satellite signals and compares this location to the known location
correction signal GPS receiver
calculates its position based on satellite signals and applies the difference
underlying premise: any two receivers that are relatively close together will experience similar atmospheric errors
• Cell of origin (COO)
– Every cell belongs to one base station
– Different frequencies are used in neighbouring cells
– Base stations know about mobile phones
within their cell
– Accuracy of the position
depends on the size of the cell
10.1 Positioning
http://www.cisco.com/c/dam/en/us/
http://emf2.bundesnetzagentur.de/karte.html
• Signal comparison
– Cell phone is in contact with several base stations – Either base station calculates the position
• Angle of arrival (AOA)
• Signal strength
• Time of arrival (TOA)
– Or cell phone calculates its position
• Signal running time difference
– Accuracy: approx. 50-200m
10.1 Positioning
http://etutorials.org/shared/
• Location transponder
– Mobile device gets location information from transponders (e.g. RFID)
– Advantages
• Quite precise: 1-5m
• May send additional information
• Suitable for indoor applications
– Disadvantages
• Mobile device needs additional software
• Transponders have to cover the whole area
• Synchronization of transponders and applications is necessary
10.1 Positioning
http://www.priority1design.com.au/
• Example: Balise (from French "baliser")
– Data is transmitted while a train passes over the Balise (transponder principle)
• Some Balises send always the same information
• Others are controlled by so-called Lineside Equipment Units (LEU)
– Receiver in the train: Balise Transmission Module (BTM)
– Components of the European Train Control System (ETCS)
10.1 Positioning
http://de.wikipedia.org/
– Technical data
• Messages consists of 1023 bits or 341 bits, payload: 830 respectively 210 bits
• Data transfer rate: 564.48 kBit/s
• It is possible to transmit a complete message up to a speed of 500 km/h
• FSK-modulated magnetic field, 3.951 MHz
equates to a logical 0 and 4.516 MHz to a logical 1
• Power supply by the BTM’s vertical magnetic field with a frequency of
27.095 MHz (electromagnetic induction)
10.1 Positioning
http://www.jd-signal.com/
– Transmitted data
• Position
• Gradient
• Speed-limit
• Next stop of the train
– Allows the on-board ETCS equipment to
• Control the compliance with speed limit and the correct direction
• Use emergency breaking in time
10.1 Positioning
https://upload.wikimedia.org/
• Peer-to-peer positioning
– Exchange of position information between mobile devices (C2C, C2X)
– Advantages
• Decentralized position information acquisition
• Position information
from specialized devices
– Disadvantages
• No standard established yet
• Chicken-and-egg problem
10.1 Positioning
https://www.car-2-car.org/
• In-car navigation systems support the driver by
– Showing the vehicle's current location on a map – Giving visual and audio information on how to
efficiently get
from one location to another
(route guidance)
10.2 Car Navigation
http://www.giga.de/apps/navigon/
• Components of a navigation system
10.2 Car Navigation
traffic reports
map section (current position)
communi- cation
sensor system mass storage
positioning map
matching
HMI routing
route guidance
digital map
traffic reports
measurements
screen speech
input keyboard
speech output
map data (off board)
> route segments
< rerouting
> operating instructions
< status
> route segments, route list
< chosen route
map section (start)
• GDF (Geographic Data Files)
– Standardized geometrical and topological model for road networks and other geographic data
– Interchange file format – Contains rules for
• Data capture
• Management
• Representation
– Nationwide GDF-data for Germany since 1995
– A GDF database (in the exchange format) will never be used as such
10.2 GDF
• Level 0: geometry and topology
– Nodes, edges and faces
• Level 1: features
– "Simple features" e.g. road segments, rivers, borders and road signs
– Features may have specific
attributes (e.g.
one way street,
roadway width,
number of lanes) and relations
10.2 GDF
http://www.ertico.com/download/misc/GDF/gdf_intro.pdf
• Level 2: complex features
– Aggregation of simple features
– Simplified representation (Generalization)
10.2 GDF
http://www.ertico.com/download/misc/GDF/gdf_intro.pdf
10.2 GDF
Junction
Road Element Level 1
Level 2
Inter- section
http://www.ikg.uni-bonn.de/vorlesungsarchiv/Gis_iv_SS_02/Vortraege/Becker.ppt
• Features are grouped into feature themes
10.2 GDF
http://www.ertico.com/download/misc/GDF/gdf_intro.pdf
• Feature Themes are divided into Feature Classes
– Example: Theme: Roads and ferries(Code 41)
Classes: 4110 RoadElement
4120 Junction
4130 FerryConnection
• Physical representation of GDF
– In ASCII files, ISO 8251-1
– A country consists of a collection of files
– A file contains several records, one for every GDF-element e.g.
a PointFeature is one (logical) record – Mediarecords of 80 signs each
– Data within one record is exactly defined by fields and length
10.2 GDF
10.2 GDF
52= Line Feature ID = 20001532 Feature Code = 4110=RoadElement Split = 0
#Edges = 1
20003220
#Faces = 0
#Attributes = 1 20002083 From 20001751 To 20001752 24 = Edge Feature
ID = 20003220 from 20002222 to 20002223 Face 20000611 Rightface 20003926 Status = 2
51 = Point Feature ID = 20001751 Feature Code = 4120 = junction
#Knots = 1
20002222
#Attributes = 0
51 = Point Feature ID = 20001752 Feature Code = 4120 = junction
#Knots = 1
20002223
#Attributes = 0 25 = New Node
ID = 20002222 XYZ-ID 20009835 Status = 2 (normal)
25 = New Node ID = 20002223 XYZ-ID 20009837 Status = 2 (normal)
44= Segm Attribute ID = 20002083
#Attributes = 6
ON Official Name 20001871 AN Alternate Name 20001872 FC Functional Road Class
1 8B Net 1 Class 3 FW Form of Way 4 Part of a roundabout DF Direction of Traffic 3 Closed in negative 41 = Name Record
ID = 20001871
GER//LANDWEHRKREISEL
41 = Name Record ID = 20001872
GERFRANKFURTER ALLEE
10.2 GDF
www.maps.google.de
• Attributes
– Simple Attributes: consists of one component
– Composite Attributes: consists of several components
→ so called Sub-Attributes
– Restrictive Sub-Attributes: restricts the validity of other attributes
→ may only be used within composite attributes
– Segmented Attributes: only valid for a part of a feature
→ position-from-, position-to-value
10.2 GDF
Feature:
Road Element
Attribut:
Speed Restriction 50 km/h
Restr.Sub-Attribute:
Validity Period 8.00 – 18.00 Uhr
10.2 GDF
http://www.ikg.uni-bonn.de/.../Becker.ppt
• Relations
– Not topological e.g. the relation ´is capital of´
between Paris and France
– Usually relations between two features
– N-nary relations also possible, e.g. a bridge leads a road over a river
10.2 GDF
http://www.ertico.com/download/misc/GDF/data_model.pdf
• Automotive navigation
– Pilotage, recognition of "landmarks"
– Dead reckoning
• Previously determined position
• Recordings of the wheel rotation and steering direction
– Inertial navigation systems (INS)
• Initially provided with the car’s position, orientation, and speed
• Recordings of motion and rotation sensors
– Radiolocation
• Measuring phase and runtime of radiowaves
• Terrestrial (e.g. UMTS) or satellite-based (GPS)
10.2 Car Navigation
www.ikg.uni-hannover.de
• Sensor system
– Wheel speed sensors
• Provide the speed of the vehicle and the covered distance
• Electronic tacho-signal
– Odometer
• Measuring the covered distance
• Change of direction can be calculated using two odometers, one each for the wheels on an axle (differential odometer)
– Electronic compass – Gyroscope
• Current sensors most often are built in micro- electro-mechanical systems technique (MEMS)
10.2 Car Navigation
http://vnc.thewpp.ca/
• Technology of very small devices
– Evolved from semiconductor device fabrication
– Materials are silicon, polymers, ceramics
• Main criterion is that there are elements having some
sort of mechanical functionality
• Microsensors convert a measured mechanical signal into an electrical signal
10.2 MEMS Sensors
http://www.fst.umac.mo/
• Kinds of sensors
– Accelerometer – Gyroscope
– Magnetometer – Thermal sensor – Pressure sensor
• Inertial sensor system:
Accelerometer + gyroscope
10.2 MEMS Sensors
http://britneyspears.ac/physics/
• Accelerometer
– Consists of a spring- mass system
– Often capacitance change due to acceleration force is used (relatively
insensitive to temperature)
10.2 MEMS Sensors
http://www.princeton.edu/
"half of a capacitor", mass, moving
"half of a capacitor", immobile spring
– Parameters
• Mass m
• Spring stiffness coefficient k
• Resonance frequency (5-22 kHz)
– Challenges
• ∆Capacity approx. 1 fF (10-15 F)
• Acceleration 1-50 g
• Application frequency < resonance frequency
– Applications
• INS, airbags
• Smart phones, hard disk head crash protection
Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 886
10.2 MEMS Sensors
http://www.conrad.de/
http://www.kfztech.de/
• Gyroscope
– Often realized as vibrating structure gyroscope – Depends on the Coriolis force
(deflecting a moving object within a rotating reference system)
– Typical device: tuning fork
• Contain a pair of masses that are driven to oscillate with equal amplitude but in opposite directions
• When rotated, the Coriolis force creates an orthogonal vibration that can be sensed
Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 887
10.2 MEMS Sensors
http://www.sandia.gov/
• Inertial navigation system
– Three gyroscopes and three accelerometers are combined in an inertial measurement unit (IMU)
– Current systems are highly integrated and cost about 5 €
(footprint: 3 mm x 4.5 mm, resolution: 0.98mg, 0.004°/s)
Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 888
10.2 MEMS Sensors
http://www.zess.uni-siegen.de/
http://www.electronicproducts.com/
• Problems
– Dead reckoning and INS: the errors are cumulative – GPS: in urban areas often
unavailable or degraded
• Goal
– Accuracy of odometer and gyroscope
– Long-term accuracy of GPS
• Solution: sensor fusion
– GPS + odometer: good but perhaps problems with turns in tunnels
– GPS + odometer + gyroscope
10.2 Car Navigation
http://gpsworld.com/wp-content/
• Sensor fusion
– Combining of data so that the resulting information is
"better" than when the
sources were used
individually
– Complex task
Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 890
10.2 Car Navigation
[MMG12]
– Odometer + steering direction position pDR – Accelerometers + gyroscopes position pINS – Satellite positioning system position pGPS
– Wanted:
position pEST = combination(pDR , pINS , pGPS)
10.2 Car Navigation
• Kalman filter
– Operates recursively on streams of noisy input data – Produces a statistically optimal estimate of the
underlying system state
(optimal filter for a linear model subject to Gaussian noise)
10.2 Car Navigation
http://www.swarthmore.edu/NatSci/
• Routing
– Search the best way in a weighted graph – Cost
• Distance
• Effective velocity
• Energy efficiency
– Algorithms (chap. 2.6)
• Dijkstra
• Bellman-Ford
• Floyd-Warshall
10.2 Car Navigation
[St12]
• Map matching
– Process of aligning a sequence of observed user positions with the road network on a digital map – Influencing factors
• Accuracy of the positioning
• Systematic error behavior of the used sensors
• Quality of the map
10.3 Map Matching
http://www.dieter.pfoser.org/
10.3 Map Matching
http://www.uni-stuttgart.de/iagb/forschung/messtechnik/projekte/mapmatching-Dateien/Cz_Internet_Strasse.pdf
– Simplified matching algorithm
10.3 Map Matching
measure position determine error region
determine possible roads
Chose "bes t"
matching does
calculated one?
region equals measured adjust position
yes no
• Point-to-Point Matching
– Match the measured position to the "closest" point (node) on the map
– Difficulties
• The position is usually not represented as node on the map it is one point on a line (street) instead
• Streets with more shape points are chosen with higher probability
10.3 Map Matching
• Point-to-Curve Matching
– Identify the road segment which is "closest" to the measured point
– Distance measures might be
• Minimum distance, mean distance, Hausdorff distance
• Let A denote the segment between a=(a1,a2) and b=(b1,b2).
The minimum distance between some point c=(c1,c2) and A is the minimum of:
with
– Shortcoming: No use of "historical" information
10.3 Map Matching
• Curve-to-Curve Matching
– A better way to proceed is to consider m positions simultaneously
10.3 Map Matching
http://ebus.informatik.uni-leipzig..../vt06-ve07-pdf.pdf
– Further criteria to evaluate the quality of a matching
• Angle between segments and the direction of movement
• Connectivity of segments
– Additional information that might help to improve the quality or reduce the
computation costs
• Allowed driving directions (one way streets, ban on turns, separated lanes)
• Driving speed e.g. helps to decide whether a car drives on a highway or a street parallel to it
10.3 Map Matching
• Threats to privacy
– Subsequent queries of a user’s location may be used to create a movement profile
– Tracking of persons possible (stalking) – Danger of a
"glassy citizen"
• Data privacy
protection necessary
10.4 Privacy
http://pixelbuy.com/Ebay/Import/GPS%20TK202/google+.jpg
• Legal aspects
– Directive on privacy and electronic communications of the European Parliament (2002/58/EC, 2009/136/EC)
10.4 Privacy
• Classification of system architectures
– Non-cooperative architecture
• Users depend only on their knowledge to preserve their location privacy
– Centralized trusted party architecture
• A centralized entity is responsible for gathering information and providing the required privacy for each user
– Peer-to-Peer cooperative architecture
• Users collaborate with each other without the interleaving of a centralized entity to provide customized privacy for each single user
10.4 Privacy
• Non-cooperative architecture
– Landmark objects
• Instead of reporting the exact location, report the location of a closest landmark
• The query answer will be based on the landmark
• Voronoi diagrams can be used to identify the closest landmark
– "False Dummies"
• A user sends m locations, only one of them is the true one while m-1 are false dummies
• The server replies with a service for each received location
• Only the user knows the true location, and hence the true answer
10.4 Privacy
http://mdm2007.uni-mannheim.de
• Centralized trusted party architecture
– Quadtree Spatial Cloaking
• Achieve k-anonymity, i.e., a user
is indistinguishable from other
k-1 users
• Recursively divide the space into quadrants until a quadrant has less than k users
• The previous quadrant, which still meet the k-anonymity constraint, is returned
10.4 Privacy
Goal: 5-Anonymity for
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
• Example
for a 9-anonymity
in a crowd of 70 people
10.4 Privacy
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
m (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
m (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
m (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
m (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
m (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Clique Cloak Algorithm
• Each user requests
– A level of k anonymity – A maximum cloaked area
• Build an undirected constraint graph
• Two nodes are neighbors,
if their maximum areas contain each other
• The cloaked region is the MBR that includes the user and neighboring nodes. All users within an MBR use that MBR as their cloaked region
10.4 Privacy
A (k=3)
C (k=2) B (k=4)
D (k=4) F (k=5)
H (k=4) E (k=3)
m (k=3)
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Nearest-Neighbor k-Anonymizing
• Determine a set S containing u and k - 1 u’s nearest neighbors
• Randomly select an element v from S
• Determine a set S’ containing v and v’s k - 1 nearest neighbors
• The MBR of all users in S’ and
u is taken as the u’s location
10.4 Privacy
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Nearest-Neighbor k-Anonymizing
• Determine a set S containing u and k - 1 u’s nearest neighbors
• Randomly select an element v from S
• Determine a set S’ containing v and v’s k - 1 nearest neighbors
• The MBR of all users in S’ and
u is taken as the u’s location
10.4 Privacy
S
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Nearest-Neighbor k-Anonymizing
• Determine a set S containing u and k - 1 u’s nearest neighbors
• Randomly select an element v from S
• Determine a set S’ containing v and v’s k - 1 nearest neighbors
• The MBR of all users in S’ and
u is taken as the u’s location
10.4 Privacy
S
S’
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Nearest-Neighbor k-Anonymizing
• Determine a set S containing u and k - 1 u’s nearest neighbors
• Randomly select an element v from S
• Determine a set S’ containing v and v’s k - 1 nearest neighbors
• The MBR of all users in S’ and
u is taken as the u’s location
10.4 Privacy
S
S’
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
– Basic Pyramid Structure
• The entire system area is represented as a complete pyramid structure
divided into grids at different levels of various resolution
• Each grid cell maintains the number of users in that cell
• To anonymize a user request, we traverse the pyramid structure from the bottom level to the top level
until a cell satisfying the user privacy
profile is found
10.4 Privacy
http://mdm2007.uni-mannheim.de/.../Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
• Peer-to-peer based systems
– Peer searching
• Broadcast a multi-hop request until at least k-1 peers are found
– Location adjustment – Spatial Cloaking
• Blur user location into
a region aligned to a
grid that cover the
k-1 nearest peers
10.4 Privacy
http://mdm2007.uni-mannheim.de/downloads/
Seminar_Mokbel_Aref_MDM_2007-05-09.ppt
• Positioning
– GPS
– Network-based locating – Location transponder
• Car Navigation
– GDF
– Sensor system
– Navigation systems – Routing
10.5 Summary
• Map Matching
• Privacy
– System architectures – Algorithms
10.5 Summary
10.5 Summary
GIS collect
manage
analyse
display
operations on
graphs
LBS
navigation systems
encryption of locations GDF
position
map matching
routing