AUTOMOBILE NAVIGATION:
`
`WHERE IS IT GOING?
`
`Robert L. French
`Consultant
`Fort Worth, TX 76107
`
`Vehicular navigation systems, digital maps, and mobile
`communications equipment are interrelated product areas that
`have large potential markets because of their wide ap-
`plicability to consumer as well as business vehicles. In the
`United States, for example, there are approximately
`150,000,000 automobiles in use, and an additional
`10,000,000 are sold each year. U.S. business fleets include
`3,400,000 automobiles, 1,600,000 light trucks and vans,
`600,000 heavy trucks, and approximately 500,000 buses.
`Digital maps and mobile data communications combine
`synergistically with vehicular navigation to multiply its
`usefulness and effectiveness, and to enhance the potential
`market for both consumer and commercial applications.
`Table I lists system capabilities that may be realized by vehi-
`cle navigation alone, by navigation in conjunction with
`stored digital maps, and in combination with both digital
`maps and data communications. Clearly, the direction and
`pace of vehicular navigation system development and deploy-
`ment will be strongly influenced by the availability of com-
`prehensive digital map data bases and supporting data
`communications.
`
`Table I. Vehicular System Capabilities
`SYSTEM
`NAVI-
`WITH WITH
`FUNCTIONAL
`GATION MAP
`DATA
`CAPABILITIES
`ONLY
`DATA COMM.
`
`X
`
`X
`
`X X
`
`X
`
`X
`
`IEEE AES Magazine, May 1987
`
`Location Information
`In-Vehicle
`
`Central Dispatch
`Route Guidance
`Historical
`
`Dynamic
`
`ABSTRACT
`
`Automobile navigation systems based on dead reckoning,
`map matching, satellite positioning and other navigation
`technologies are under active development. “Map in-
`telligent” systems achieve high relative accuracy by
`matching dead-reckoned paths with road geometry encoded
`in a digital map data base that may also serve other func-
`tions such as vehicle routing and geocoding. Satellite-based
`navigation systems achieve high absolute accuracy but
`require dead reckoning augmentation because of signal aber-
`rations in the automotive environment. Future systems will
`probably include multiple navigation technologies. Issues in-
`fluencing the design of future systems include safety con-
`cerns regarding the driver interface, and the future availabili-
`ty of comprehensive map data bases, real-time traffic data,
`and mobile data communication links necessary for on-board
`generation of optimum routes.
`
`INTRODUCTION
`
`The capabilities and functions of automobile navigation
`systems in the 1990s will be shaped by important issues en-
`countered in the 1980s.
`
`0 Choosing Technology Paths
`0 Integrating Overall Systems
`0 Resolving Driver Interfaces
`0 Providing Map Data Bases
`0 Coordinating Mobile Communications
`
`This paper reviews each of these issues, and discusses possi-
`ble scenarios for the future based upon current directions
`here and abroad. It is a companion piece to an earlier paper
`which traces the history of automobile navigation and
`describes contemporary navigation technologies [1].
`
`Based on a presentation at PLANS ’86.
`0885-8985/87/0500-0006 $1.00 © 1987 IEEE
`
`6
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`Google Exhibit 1008
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`Page 1 of 7
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`

`
`xoooo
`
`_ CELESTIAL
`
`--.-- RADIO LOCATION
`
`A MAP MATCHING
`
`I000
`
`100
`
`‘O
`
`\
`- ~\
`
`ETAK
`
`IAVSTAR
`
`
`
`
`
`POSITIONACCURACY(meters)
`
`1940
`
`I960
`
`YEAR
`
`I960
`
`2000
`
`Figure 1. Improvements in Position Accuracy
`
`TECHNOLOGY PATHS
`
`The effectiveness of navigation technology is traditionally
`rated in terms of position accuracy. Figure 1 shows the im-
`provements in accuracy that have been achieved in recent
`decades with multi—purpose radio-location technologies as
`reported by Luse and Malla [2]. The accuracy of celestial
`navigation in 1940 [2], and the accuracy of recent map
`matching technologies reported by French and Lang [3] and
`by Honey and Zavoli [4] are included for comparison.
`
`Radio Location
`
`The exponential improvement in radio-location accuracy
`with time is striking, but it should be noted that the target
`date of 1988 for Navstar Global Positioning System (GPS)
`availability will not be met as a result of the presently
`diminished U.S. capacity for launching satellites. Loran is
`now gaining some popularity as a means of tracking land
`vehicle location from a central location [5,6], but its modest
`accuracy, along with the persisting lack of mid—continent
`coverage, limits its usefulness for automotive navigation.
`Although the absolute accuracy of Navstar GPS has great
`appeal for future automotive navigation,
`it is not the panacea
`inferred by reports following Chrysler’s introduction of the
`CLASS concept at the 1984 World Fair in New Orleans [7]
`and the investigation of satellite navigation by other
`automobile manufacturers [8]. GPS signal disruption by
`buildings, bridges, foliage, etc., may produce positioning
`discontinuities when GPS receivers are operated in
`automobiles. Auxiliary dead reckoning subsystems are thus
`
`IEEE AES Magazine, May 1987
`
`Page 2 of 7
`
`required for effective automotive navigation using GPS.
`Other future satellite systems may also offer vehicle
`navigation as well as mobile data communication services
`[9]. In addition, there is potential for new radio-trilateration
`approaches using subcarrier signals from cellular radio
`transmitters [10].
`
`Dead Reckoning
`Dead reckoning is the process of determining a vehicle’s
`location relative to an initial position by integrating measured
`increments and directions of travel. Most dead reckoning
`technologies used in automobile navigation systems were
`developed long before the automobile itself [1]. These in-
`clude the odometer, the differential odometer, and the
`
`magnetic compass. The gyro compass, developed in 1906,
`has seen only limited use in automobile systems, and inertial
`systems are presently expensive and ill—suited for the harsh
`automotive environment.
`
`Dead reckoning accuracy is difficult to quantize because it
`continuously decreases with time and/or the distance a vehi-
`cle is driven. For example, the vehicular odograph, a WW-
`II military navigation system based on the odometer and
`compass, accumulated 1 mile of error per 50 to 150 miles
`driven [11]. Even the most precise dead reckoning naviga-
`tion systems require periodic reinitialization.
`
`Map Matching
`Artificial intelligence concepts may be applied to match
`dead—reckoned vehicle paths with road maps which are
`digitized and stored in computer memory. With map
`matching, sensed mathematical features of the vehicle path
`are continuously associated with those encoded in a map data
`base, just as a driver associates observed landmarks and road
`features with those depicted on a paper map to recognize
`position. Thus a vehicle’s dead—reckoned location may be
`automatically reinitialized at every turn to prevent accumula-
`tion of dead reckoning error.
`The first vehicular application of map matching technology
`was in the Automatic Route Control System (ARCS) which
`used a differential odometer for dead reckoning [3]. ARCS
`had an average location accuracy of 1.15 meters (see Figure
`1) relative to predetermined routes that were initially digi-
`tized by direct fleld measurements using the ARCS equip-
`ment. Since the digital route map data were from replicable
`field measurements, the 1. l5—meter location accuracy is
`more a measure of the effectiveness of the map matching
`algorithm rather than the accuracy of the dead reckoning
`technique or of the map data being matched.
`The more recent Etak map—matching system uses a solid
`state flux-gate compass as well as the differential odometer
`to dead reckon paths for matching with digitized maps com-
`piled from Census Bureau GBF/DIME files, U.S. Geological
`Survey topographical maps, and aerial photographs [4]. As
`shown in Figure 1, the Etak system exhibits an accuracy of
`approximately 16 meters relative to the digitized maps. The
`Etak map data base is within 16 meters of ground truth, and
`has a relative accuracy of 5 meters on each map according
`to Dial [12].
`
`Interestingly, neither the source nor the magnitude of dead
`reckoning and map data errors need be overriding concerns‘
`
`7
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`Page 2 of 7
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`

`
`when map matching is used. As long as the street and road
`connectivity is accurately defined, the map matching process
`identifies position relative to the road network as visually
`perceived by the vehicle driver. The information actually
`needed by the driver may thus be presented in a customary
`frame of reference. After all, vehicle location coordinates
`
`are of little value to a driver unless used in conjunction with
`a map [13].
`Even relatively crude dead reckoning is sufficiently robust
`to support map matching when operating on a defined road
`network. However, good dead—reckoning accuracy is re-
`quired to achieve reinitialization through map matching upon
`returning to the road network after off—road operation such
`as in a parking lot.
`
`DISTANCE
`SENSOR
`
`HEADING
`SENSOR
`
`LOCATION
`SEX son
`
`MAP DATA
`
`5‘ 55
`
`NAVIGATION
`
`COMPUTER
`
`DATA
`TRAN SCEI VER
`
`OUTPUT
`
`DESTINATION
`I "PUT
`
`VISUAL
`
`AUDIO
`OUTPUT
`
`Proximity Beacon
`
`Figure 2. Future System Configuration
`
`This approach uses strategically located short—range
`transmitters, and the very reception of their location-coded
`signals infers the receiving vehicle’s instantaneous location.
`Several variations of the proximity approach, some involving
`two-way communications with equipped vehicles, have been
`investigated for interactive route guidance [14]. Typically,
`the driver enters a destination code on the vehicle panel for
`automatic transmission to a roadside unit as the vehicle ap-
`proaches an instrumented intersection. The roadside unit,
`which may be networked with a traffic management system,
`analyzes the destination code and instantly transmits route in-
`structions for display on the vehicle’s panel. Alternatively,
`the roadside unit may only transmit its location to the vehicle
`where an on—board computer, using stored road network
`data, generates the route instructions from the identified
`location.
`
`The proximity beacon approach, inactive in the U.S. since
`Congress mandated termination of the ERGS project in 1970
`[15], has been the subject of further development and testing
`in Japan [16] and West Germany [17] where the task of in-
`strumenting the road networks is less formidable. For exam-
`ple, the ALI-SCOUT proximity beacon system, which uses
`dead reckoning and map matching techniques between
`beacons which download updated map and traffic data, is
`nearing testing in West Berlin [18].
`
`FUTURE INTEGRATED SYSTEMS
`
`What configurations will prevail in automobile navigation
`systems of the future? Patterns already set in the design of
`other automotive systems, as well as computer and entertain-
`ment systems, suggest commonality and modularity as likely
`system characteristics.
`
`Figure 2 isone concept for the type of general purpose
`systems likely to appear in the next 15 years. It represents a
`composite of state-of—the-art developments, provides the
`modularity necessary for adaptation to specific applications,
`and leaves room for vendor differentiation.
`
`Distance and heading sensing will be included even if
`precise location sensing, such as Navstar GPS,
`is available.
`Distance and heading sensing may be accomplished by dif-
`ferential odometry using input signals from existing antilock
`braking systems, or in combination with software compen-
`sated flux-gate magnetic compasses. The fibre optics
`
`8
`
`Page 3 of 7
`
`gyroscope [19] also shows potential as an inexpensive and
`rugged means for accurately sensing heading changes.
`Digitized maps are as essential to the automotive naviga-
`tion systems of the future as paper maps and charts were to
`the professional maritime navigators of the past. Large
`capacity storage is required for useful amounts of map data.
`Cooke estimates that 60 percent of the U.S. population lives
`on about one million streets represented in the Census
`Bureau’s GBF/DIME files [20]. Assuming 120 to 150 bytes
`per street, simple extrapolation allowing for rural areas sug-
`gests that a nationwide digital map would fit on one 500
`MByte CD—ROM disk.
`
`Map matching systems based upon dead reckoning alone
`can become confused if digital maps are not current, or from
`extensive driving off the defined road network. Thus ab-
`solute location sensors, such as satellite positioning or prox-
`imity beacons, will be required if occasional manual
`reinitialization is to be avoided.
`Data communications will also be a feature of future
`
`systems in countries that integrate traffic management with
`in—vehicle route guidance to enhance the benefits. One-way
`communication from the infrastructure to the vehicle is the
`
`most useful link. However, additional system benefits would
`be provided by vehicle—to-infrastructure data communica-
`tions. This could provide destination information to central
`traffic management systems for planning optimal traffic flow
`or, as in the case of the ALI-SCOUT [18], eliminate the
`need for traffic sensors by reporting recent travel experience
`to the central traffic management system.
`The lower three blocks of Figure 2 comprise the driver in-
`terface, an important and controversial topic which is
`discussed separately.
`
`DRIVER INTERFACES
`
`The approach to the interface between an on—board naviga-
`tion system and the vehicle operator must take into account
`ergonomics and safety considerations as well as functional
`requirements. Most systems proposed or developed to date
`use detailed map displays or some combination of symbolic
`graphics, alphanumeric messages, and audio signals.
`
`IEEE AES Magazine, May 1987
`
`Page 3 of 7
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`

`
`There is considerable information available to automotive
`
`systems design engineers on display and control surface loca-
`tion, display brightness, contrast, color, font type, character
`density, analog vs digital representation, and many other
`signal properties have been well defined as a result of many
`years of intensive aerospace research. Good sources of data
`are also available that specifically relate to automobile and
`traffic control device designs. However, considerably less in-
`formation is available on when to present information to
`motorists; priorities for presentation of different types of in-
`formation; temporal, spatial, and modal redundancy; and
`resolution of apparent conflicts in information derived from
`outside and inside the vehicle [21].
`Insights on the driver interface issue may be gained by
`reviewing approaches that have been tried or proposed here
`and abroad.
`
`United States
`Some of the most serious research on driver interfaces was
`
`in connection with the ERGS project of the late 1960’s [22].
`The ERGS vehicle unit back-illuminated various combina-
`
`tions of arrows and words on a guidance panel. Tests were
`also conducted with “heads up” displays which projected
`simple combinations of arrows and words on the windshield
`so that the driver did not have to remove his eyes from the
`
`,
`road [23].
`Safety concerns about automotive use of CRT displays and
`elaborate control panels more typical of aircraft are
`exemplified by those of Zwahlen [24]. He points out the
`potential for visual overload leading to impairment of lateral
`steering control.
`In the early 1970s, ARCS, an automatic route control
`system developed for operation over programmed newspaper
`routes, used prerecorded audio route guidance instructions
`during extensive operational tests [3]. This approach worked
`well, but tape recorded audio instructions were awkward to
`prepare and control, and systhesized speech was not yet
`available. Therefore, an improved version used a plasma
`display panel to give route guidance in the form of shaped
`arrows along with street names, etc. [25]. Subsequent
`research reported by Streeter [26] established that drivers
`who listened to directions drove to destinations in fewer
`
`miles, less time, and with about 70 percent fewer errors than
`drivers using customized route maps.
`The next generation of systems development in the United
`States used CRT displays for the driver interface. These in-
`clude satellite—based navigation systems demonstrated by
`Ford [27], General Motors [28], and Chrysler [7], all of
`which displayed detailed map images. The Etak Navigator,
`the only advanced automotive navigation system actually on
`the market in the U.S., carries the trend a step further by
`displaying a map that rotates to match vehicle heading [4].
`
`Europe
`
`European automobile navigation system designs seldom use
`elaborate visual displays for the driver interface. The prin-
`cipal exception is the Philips CARIN system [29] which in-
`cludes a color CRT map display for showing vehicle location
`relative to the surroundings. CARIN includes synthetic voice
`
`IEEE AES Magazine, May 1987
`
`Page 4 of 7
`
`for conveying instructions to the driver when operating in
`the route guidance mode.
`The earliest example of a route guidance system incor-
`porating automatic route generation using on—board digital
`maps was “Micropilot” developed in England in 1981 [30].
`This system used an audio interface in the form of digitized
`voice — not speech synthesis — with a vocabulary of twenty
`six words.
`
`West German designs invariably use simplified visual
`displays, sometimes in combination with audio messages, for
`conveying route instructions to the driver. Virtually all West
`German systems to date use some combination of short
`visual messages, symbolic graphics, and/or voice.
`One example is the route guidance system described by
`Haeussermann in a 1984 paper [31]. When on highway net-
`works, this system uses a 2—line LCD display with 16
`characters per line to give the next route point and remain-
`ing distance. When on city streets, an alternate LCD display
`with a pointer indicates the direction of the destination, and
`shows numerals to indicate the remaining distance.
`The first generation EVA system developed by Bosch-
`Blaupunkt also uses simplified graphics to convey route in-
`structions [32]. The original prototype includes differential
`odometer, map data base with map matching, and route
`search software to generate explicit route guidance instruc-
`tions. The main display includes a vertical LCD panel for
`graphics and a small horizontal LCD strip for character
`display. Voice capability is included, and is used to confirm
`destination entries. Turns at complicated intersections, lane
`changes, etc., are specified to the driver in the form of
`simplified diagrams which show lane boundries and use ar-
`rows to indicate the path to be taken.
`Bosch-Blaupunkt also provides the interface equipment for
`the ALI-SCOUT system, a joint project of the West German
`Government, Siemens, Volkswagen, Blaupunkt and others.
`ALI-SCOUT is also a route guidance system, but rather than
`being autonomous, it depends upon the reception of area
`road network data and recommended route data broadcast
`
`from strategically located IR beacons [18]. Driving directions
`are presented much the same way as in EVA, but with an
`additional feature similar to the “Wolfsburg wave” [33].
`The Wolfsburg wave is essentially a bar graph that, in this
`application, gives a “count down” to the exact point where
`the vehicle is to turn, thus clearly delineating among closely
`spaced turns.
`
`Destination input, as well as system control, for the next
`generation of ALI-SCOUT (which will be subjected to large
`scale user tests in West Berlin starting next year) .will be via
`a hand held wireless remote control unit with shift keys for
`alphanumeric information. Thus initializing the system for a
`trip will be much like remotely programming a VCR, and
`may be done by anyone in the automobile.
`
`Japan
`Current driver interface approaches for Japanese
`automobile navigation systems seem to align more with those
`of the U.S. than with Europe. However, Japan’s first major
`step toward route guidance was the CACS (Comprehensive
`Automobile Traffic Control System) project [16] of the
`1970s which was patterned after the U.S. ERGS (Electronic
`
`9
`
`Page 4 of 7
`
`

`
`Route Guidance System) project of the late 1960s [22]. Like
`ERGS, CACS used simple combinations of direction in-
`dicators and descriptors to indicate routes to be taken.
`Autonomous navigation systems started appearing in Japan
`in the early 1980s. The Nissan Driver Guide System [34]
`displayed information in a simplified graphical form “in
`order to make the bearings and distance to the destination
`easily viewable while driving.” Directional arrows showed
`the direction to the destination, and a bar graph indicated the
`fractional distance remaining.
`Appearing about the same time was the Honda “Electro
`Gyro-Cator” navigation system [35] which used a CRT
`display to show a plot of the vehicle’s path. Location could
`be established by using a transparent map overlay.
`Subsequent systems shown in Japan incorporate color CRT
`map displays. These include systems displayed by several
`automobile manufacturers at the October 1985 Tokyo Auto
`Show [36]. Another example of current directions is a
`Loran—based Nissan delivery truck system which also uses a
`color CRT map display [37].
`A new integrated systems approach currently under joint
`development by Japanese industry and government groups
`potentially includes an on-board computer, CRT display,
`compact disk with road network data, dead reckoning sen-
`sors, roadside electronic signposts for location confirmation
`as equipped cars pass within range, and map matching to
`augment dead reckoning between signposts [36].
`
`MAP DATA BASES
`
`“Not since cartographer Gerardus Mercator started map-
`ping the world as round instead of flat in the 16th century
`has the science of map making been as stirred up.” Thus
`observed the Wall Street Journal in an April 18, 1985 article
`on the impact of digital maps on cartography. Indeed, the in-
`troduction of the computer to map making is being hailed as
`a revolution that might be comparable to the development of
`the printing press. The market for computer mapping
`systems is expected to grow from $250 million to $1 billion
`during the last half of this decade [38].
`Irrespective of the progress being made in preparing and
`using maps in digital form, a major barrier to widespread
`implementation of vehicular navigation systems will be the
`lack of comprehensive map data bases to support advanced
`navigation functions such as route guidance. Developing and
`maintaining the large amounts of map data required are cost-
`ly tasks that are difficult to justify commercially until enough
`map data is available for realistic feedback on the demand
`[13].
`The most extensive body of vector—encoded map data is
`the GBF/DIME (Geographic Base File/Dual Independent
`Map Encoding) System developed by U.S. Census Bureau
`for virtually all Standard Metropolitan Statistical Areas
`(SMSA). GBF/DIME includes street names and address
`ranges_between nodes, as well as a variety of information
`not relevant to vehicle navigation. This map data base has
`numerous errors and represents the street network as of 1977
`[20]. Nonetheless, it is a highly useful resource as it pro-
`vides an established map encodingapproach which is ap-
`
`10
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`Page 5 of 7
`
`plicable to digital maps for use with vehicular navigation
`systems.
`
`In particular, graph theory is used as a conceptual
`framework for mathematically defining the location of all in-
`tersections and the interconnecting streets or roads, thus
`reducing conventional road map information to computer
`files. Road geometry is modeled in terms of nodes and
`segments with nodes representing the location of intersec-
`tions, turns, etc., and connecting segments representing in-
`crements of road.
`
`In order to discuss map data requirements for vehicular
`navigation systems it is necessary to consider the functions
`to be performed [13]. The driver presumably needs a user
`friendly road map for trip planning, vehicle location, orienta-
`tion, etc. Digitized map data is also needed for map match-
`ing regardless of what location technique is used. A third
`use of digital map data is for automatic routing, an especial-
`ly demanding application which requires that the map data
`base include information on traffic directions, turn restric-
`
`tions and other ephemeral data. Other digital map uses
`relating to vehicle navigation include geocoding (what is the
`location of a specific address?) and location directory (where
`is the nearest garage?).
`Standards for digital map data bases are not yet available
`although the newly organized Automotive Navigational Aids
`Subcommittee of the Society of Automotive Engineers (SAE)
`has formed a task group to address the need for map data
`base standards. Nonetheless, one automobile navigation
`systems company, Etak, Inc., has undertaken development of
`a proprietary digital map data base for the entire U.S. [4].
`The Etak map data base will support navigation systems
`which display vehicle location, destination, etc., relative to
`the road network, as does Etak’s own system and the version
`being developed under license by General Motors for in-
`troduction in 1989. Systems which automatically generate an
`appropriate route to an input destination will require a map
`data base containing additional attributes as described above.
`
`MOBILE DATA COMMUNICATIONS
`
`Major potential roles for data communications in future
`automobile navigation systems will be to provide current up-
`dates (road additions, closures, detours, etc.) for on-board
`map data bases, and to provide real—time information on traf-
`fic conditions for systems that include on-board route genera-
`tion. Mobile data communications offer additional advantages
`for commercial vehicles using navigation systems, including
`centralized vehicle location monitoring and dispatch control.
`Mobile cellular radio offers great potential for two-way
`data communications with vehicles equipped with navigation
`systems. As the public adopts the idea of the “mobile of-
`fice”, there will be considerable demand for cellular radio
`
`for the transmission of data as well as voice. The necessary
`modems are already beginning to appear on the market [39].
`For one—way data communications with vehicle navigation
`units, an alternative area broadcast approach such as the
`Radio Data System (RDS) proposed by the European Broad-
`casting Union [40] may be advantageous. This enables digital
`information to be superimposed on the normal broadcasts of
`FM radio stations by means of sub—carrier modulation.
`
`IEEE AES Magazine, May 1987
`
`Page 5 of 7
`
`

`
`Although appropriate technologies may be available for
`communicating updated map and traffic data to vehicular
`systems, there are numerous institutional barriers to the im-
`plementation of supporting data communications. Standards
`are not only required for the frequency, modulation tech-
`niques, communications mode, error detection and correction
`techniques, etc., but the data content of transmissions should
`follow a standard structure. Some progress has been made
`on these issues in vehicular navigation in Europe [40], but
`efforts to address these requirements in the U.S. have not
`yet been initiated.
`A critical prerequisite for dynamic route guidance is coor-
`dination among traffic authorities at the local, regional, state
`and national levels for the uniform collection and dissemina-
`tion of traffic information for communication to vehicular
`
`systems. Without initiative on the part of the federal govern-
`ment, there does not appear to be a viable mechanism for
`bringing about the necessary coordination in the U.S.
`
`CONCLUSIONS
`
`The various technologies required for future automobile
`navigation and route guidance systems that will relieve
`drivers from the tedium of planning routes and finding the
`way over them have already been developed, or are within
`reach. The main developments yet to come are in the infor-
`mation and institutional areas. In particular, large private
`sector investments will be required for the development and
`maintenance of comprehensive digital map data bases, and
`coordination among public sector organizations will be re-
`quired for collecting, standardizing, and communicating real-
`time information on traffic and road conditions.
`
`REFERENCES
`
`1. R. L. French, “Historical Overview of Automobile Navigation
`Technology,” Proceedings of the 36th IEEE Vehicular Technology Con-
`ference, 350-358, Dallas, Texas, May 20-22, 1986.
`
`2. James D. Luse and Rajendra Malla, “Geodesy from ASTROLABE to
`GPS — A Navigator’s View,” Navigation, Vol. 32, No. 2, 101-113
`(Summer 1986).
`
`3. R. L. French and G. M. Lang, “Automatic Route Control System,”
`IEEE Transactions on Vehicular Technology, Vol. VT-22, 36-41
`(1973).
`
`4. S. K. Honey and W. B. Zavoli, “A Novel Approach to Automotive
`Navigation and Map Display,” RIN Conference Proceedings “Land
`Navigation and Location for Mobile Applications," York, England
`(1985).
`
`5. R. V. Janc, “Consideration of the Various Error Sources in a Practical
`Automatic Vehicle Location System, " 34th IEEE Vehicular Technology
`Conference Record, 277-284 (1984).
`
`6. R. Bronson, W. Sears and L. Cortland, “II Morrow’s Loran C Based
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`Navigation and Location for Mobile Applications, ” York, England
`(1985).
`
`7. M. Lemonick, “Now: Driving by Satellite," Science Digest, 92, 34
`(1984).
`
`8. D. Gable, “Automobile Navigation: Science.Fiction Moves Closer to
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`IEEE AES Magazine, May 1987
`
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`
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