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 Chapter 3. Navigation Systems A Spatial
Database Perspective
Choi Jae-Ho redcolor25_at_korea.ac.kr http//mobide.
korea.ac.kr Mobile Data Engineering Lab. Dept. of
Computer Science and Engineering, Korea
University
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Contents

• Introduction
• Navigation Systems
• Spatial Databases
• Services
• Gateway Service
• Location Utility Service
• Directory Service
• Route Determination Service
• Presentation Service
• Conclusion

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Introduction

• Navigation systems
• Guide objects moving from one place to another
• Have progressed recently with the rapid advances
  in positioning, communication, and spatial data
  storage and processing technologies
• The LBSs require a spatial DB (SDB)
• The core services of LBS
• Location utilities services
• Directory services
• Presentation service
• Gateway service
• Route determination service

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Navigation Systems

• A modern navigation system
• An integrated collection of position and
  orientation sensors and computing and
  communication hardware and software used to
  facilitate the movement of people, vehicles, and
  other moving object from one place to another
• The components can be broadly classified into
  four subsystems
• Spatial databases server
• GeoMobility server
• Communication systems
• Location-Aware clients

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Navigation Systems

• Architecture of a modern navigation system

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Navigation Systems

• Spatial database server
• An SDB server is an essential component for
  building efficient navigation system applications
• It provides conceptual, logical, and physical
  data modeling facilities

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Navigation Systems

• Open location services and GeoMobility server
• The OGC (i.e. international consortium for
  developing publicly available geoprocessing
  specifications) recently initiated an Open
  Location Services Initiative
• The purpose of the Initiative is to produce open
  specifications for interoperable location
  application services
• The GeoMobility server is an OpenLS platform
  through which content/service providers can
  deliver and service location-based applications

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Navigation Systems

• The core services
• Location utilities service
• The OpenLS utilities specification provides two
  services, geocoding and reverse geocoding
• Directory service
• The directory service provides a search
  capability for one or more points of interest
  (POI) or area of interest (AOI)
• where is the nearest Thai restaurant to the
  EE/CD department?
• Presentation service
• This service deals with visualization of the
  spatial information as a map, route, and/or
  textual information

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Navigation Systems

• Gateway service
• This service enables obtaining the position of a
  mobile terminal from the network
• Route determination service
• This service provides the ability to find a best
  route

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Navigation Systems

• Communication systems
• Telecommunications have undergone significant
  changes in the last 30 years
• LAN, WAN
• The most recent advance in telecommunications is
  wireless telephony, commonly know as cell phones
• Location-based services are dependent on both
  wired and wireless networks

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Navigation Systems

• Location-Aware Clients
• Three basic components
• A position and orientation module
• A computing module consisting of display and
  storage
• A communication module
• Each client-side module may not necessarily be
  equipped with all three modules but still can be
  part of a location-based application

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Spatial Databases

• Digital Road Maps
• Traditionally, digital road maps were available
  through governmental departments
• Due to commercial demand, several private-sector
  companies have begun to offer digital road maps
  with additional points of interest and areas of
  interest information
• Data quality refers to the relative accuracy and
  precision of a particular GIS database

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Spatial Databases

• Digital road map sources

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Spatial Databases

• Four components of data quality standards
• Lineage
• Refers to the narrative of source materials
  (e.g., USGS quad sheets) used and procedures
  (e.g., map projection, map generalization)
  applied to produce the product
• Positional accuracy
• Defines expected error in position of features
  (e.g., landmark points)
• Attribute accuracy
• Defines expected error in attributes (e.g., road
  name)
• Completeness
• Defines the fraction of real-world feature
  depicted on a map

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Spatial Databases

• A summary of claims from different sources
• TIGER mean error¼281 feet (90 m), Median
  error¼166 feet(50 m). 90th percentile from 110m
  to 440m across different sources
• Basemap 40 feet at 124,000 scale, 166 feet at
  1100,000 scale using NMAS
• NavTech 97 accuracy, percent error¼linear
  combination of 13 component errors
• Etak 40 feet at 124,000 scale (cover 70 of
  U.S. population), 166feet at 1100,000 scale
  (covers another 25 of U.S. population), using
  NMAS
• GDT In enhanced regions, 5m to 7m

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Spatial Databases

• Data Model of Digital Road Maps
• Database application is modeled using a three
  step design process
• Conceptual data model
• Logical modeling
• Physical design

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Spatial Databases

• Conceptual data model
• At the conceptual level, the focus is on the data
  types of application, their relationships, and
  their constraints
• The Entity Relationship (ER) model is one of the
  most widely used conceptual design tools
• But, it has long been recognized that it is
  difficult to capture spatial semantics with ER
  diagram
• Several researchers have proposed
  pictogram-enhanced ER (PEER)

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Spatial Databases

• A PEER diagram

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Spatial Databases

• Logical data model
• The logical modeling phase is related to the
  actual implementation of the conceptual data
  model in a commercial DBMS
• The actual mapping between a PEER model and OGIS
  (i.e. OpenGIS)/SQL3(i.e. recently standardized)

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Spatial Databases

• Physical data model
• In the physical data modeling phase, issues
  related to storage, indexing, and memory
  management are addressed
• Physical database design is critical to ensure
  reasonable performance for various queries
• No natural total order is defined on point in a
  multidimensional space
• Hashed and ordered file organization (e.g., B
  tree) cannot be used directly

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Spatial Databases

• A fundamental idea in spatial indexing is the use
  of approximations
• The prime example is the bounding box
• Well-known spatial indexing structures are R-tree

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Spatial Databases

• Several location-based services, especially,
  those that deal with network databases (e.g.,
  road network)
• Have to deal with efficient network computation
• Different representations of a graph

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Spatial Databases

• The directed graph representation
• Often used to speed up shortest path computation
• Query types for directory service

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Gateway Service

• Gateway service
• The interface between the Open Location Service
  Platform and Mobile Positioning Servers
• Obtains near real-time position data and
  orientation data
• Three types of positioning systems
• Stand-Alone
• Satellite-Based
• Radio-based

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Gateway Service

• Stand-Alone positioning systems
• Deduced reckoning (DR) is the typical stand-alone
  technique to determine current position with
  reference to a starting position
• DR incrementally integrates the distance and
  direction relative to the known start position

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Gateway Service

• Satellite-Based positioning systems
• That is widely used in modern vehicle navigation
• GPS consists of three parts
• The space segment (i.e. a constellation of 24
  operational satellites)
• The user segment (i.e. GPS receivers)
• The control segment (i.e. consisting of
  monitoring stations, ground antennas, and
  coordinating master control station)

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Gateway Service

• (Terrestrial) Radio-Based positioning system
• Radio-based positioning systems are designed for
  specific applications
• These systems are generally managed by government
  and military/naval agencies
• Indoor navigation systems generally use infrared
  and short-range radios (e.g. RFID)
• The mobile networking community uses a technique
  known as Cell Identification (Cell-ID)

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Location Utility Service

• The OpenLS utilities specification provides two
  services
• Geocoder and reverse geocoder
• Geocoding
• Geocoding is the process of assigning an x, y
  coordinate to a given address
• Incase of ambiguities, the approximate location
  can be computed as the centroid of the zip code

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Location Utility Service

• Reverse geocoding
• Reverse geocoding is exactly the opposite of
  geocoding
• Find the address given an x, y coordinate
• The coordinates predicted by the GPS receiver
  contain error
• Map matching
• We need identify the most likely segment of load
  network
• Map matching techniques can be classified as
  geometric, probabilistic, and fuzzy

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Location Utility Service

• Geometric
• Point to point matching
• The objective is to find the closest node ni to
  the measured point P
• Point to curve matching
• The objective is to find the closest curve from
  the measured point P
• Curve to curve matching
• More accurate geometric method, uses the
  piecewise linear curve

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Location Utility Service

• Probabilistic
• The probabilistic algorithms first compute a
  confidence region along the measured track (e.g.
  GPS track)
• If more than one road segment is found within
  estimated region, then the most probable road
  segment is estimated using various checks (e.g.
  road network topology, history)
• Fuzzy logic
• Expert rules (e.g. such as amount of distance
  traveled and directional changes in the heading
  of the vehicle) are assigned fuzzy membership
  functions

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Directory Service

• The directory service of LBS provides a search
  capacity for one or more POI

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Directory Service

• Nearest neighbor methods

Selected nearest neighbor
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Route Determination Service

• Route determination services address finding
  route and navigation information between
  locations
• That services should support two services
• Determination of new route, find best path
• Fastest, shortest, easiest etc
• Avoid location, highway, tollways, U-turns etc.
• Determination of alternate routes
• Have minimal overlap with existing route

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Route Determination Service

• Path-Query processing
• An important ingredient in spatial network
  applications
• Graph traversal algorithm
• Dijkstras algotithm
• Best-first A algorithm
• Heuristic search using semantic information about
  a domain
• It is faster than Dijkstra's algorithm.
• Cost(s, d) g(s, v) h(v, d)
• G(s,v) is the cost from s to v, h(v, d) is the
  estimated cost.
• widely used in games etc.

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Route Determination Service

• p is the point being checked
• g is the cost to get from the starting point to p
• h is the estimated distance to the goal from p
• f represents the estimated "goodness" of the
  point
• f(p) g(p) h(p)

• Best-first A algorithm
• 1. Let P the starting point
• 2. Assign f, g, h value to P.
• 3. Add P to the Open list. At this point, P is
  the only on the Open list.
• 4. Let B the best node from the Open list
• a. If B is the goal node, then quit (success)
• b. If the Open list is empty, the quit (fail)
• 5. Let C a valid node connected to B
• a. Assign f,g,h value to C
• Check whether C is on the Open or Closed list.
• If so, check whether the new path is more
  efficient( lower f-val)
• If so, update the path.
• Else, add C to the Open list.
• Repeat step 5 for all valid children of B.
• 6. Repeat from step 4.

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B
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E
D
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2
A
C
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Route Determination Service

• Memory bounded search algorithms
• Previously introduced algorithms assume that the
  system has unlimited memory that can hold all
  information used in these search algorithms
• Algorithms that are designed to work with modest
  memory requirements
• IDA (interative deepening)
• SMA(simplified memory-bounded)
• Hierarchical Strategies
• Decompose large spatial graph into a collection
  of fragment graph

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Route Determination Service

• Summary of path-finding results

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Presentation Service

• Presentation services display road maps and
  overlay routes, points of interest, object
  locations, and/or text information
• Currently, most presentation services are
  provided based on a visual interface framework
• However, in the future a voice-based interface
  will likely be adopted

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Presentation Service

• Route guidance
• Presentation service requires efficient
  route-guidance algorithms to dynamically process
  and present the guidance instructions
• The process that guides travelers along a route
• Use simple display icon for forthcoming action
• Two kinds of route guidance models
• Centralized model
• Route computation occues in center (Cellular
  phone navigation)
• Distributed model
• PDA, special navigation device, High computing
  power is required

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Conclusion

• Research needs