CHAPTER14ECDISANDTHEINTEGRATEDBRIDGEINTRODUCTION1400.OperatingConceptCollisionAvoidanceBridge watch officershavethree main duties:.Watchofficers evaluatethe contactsituation and cal-culate the closest points of approach (CPA's) forNavigationvarious contacts..Watchofficers maneuver in accordancewiththeRules.Watchofficersprocessnavigation informationfromofthe Roadto avoid close CPA'sand collisionsseveral different sources.They take fix positionsfrom satellite and hyperbolic receivers. They mea-Ship Managementsure bearing lines and radar ranges to suitableNAVAIDS.Theythenplotthis informationonapa-.Watch officers conduct evolutions that are part ofanper chart.individual ship's routine.Afterplottingthe information ona chart, watchof-ficers evaluate the navigation picture. TheyThe integrated bridge is designed to reduce the timedetermine if the ship's present position is a safe onespent on navigation by eliminating manual data processingand providing the navigator with a display which aids himTheyprojectthe ship's position ahead and plan forinquickly evaluating the navigationpicture.future contingencies.The evaluation step isthemostimportant step inthenavigationprocess.ProperlyPreliminary studies seem to indicate that time spent onexecuting this step is a function ofthewatch officnavigation as a percentageof total watch officer dutieser's skill and how well the ship's actual navigationdrops significantly when using the integrated bridge.Thissituation is represented on the chart.That represen-does not necessarilylowerthe overall watchofficer work-tationinturn.isafunctionofbothplotterandsensoload, but it does increase the percentage of time he canaccuracy.devoteto ship management and collision avoidanceTHEINTEGRATEDBRIDGE1401.SystemComponentsofficer.Thesystem'scomputernetworkprocessestheposi-tioning information and controls the integrated bridgeThe term"integrated bridge"encompasses several pos-System's display and control functions.sible combinations of equipment and software designed.Chart Data Base: At the heart of any integrated bridgespecifically for each individual vessel's needs.Therefore,each integrated bridge system is different.This section in-system lies an electronic chart.An electronic chart systemtroduces, in general terms, the major equipment likely to bemeetingInternationalMaritimeOrganization(IMO)specifi-found in an integrated bridge systemcationsfor complying with chartcarrying requirements is anElectronicChartDisplay and Information System (EC-.Computer Processor and Network:This subsystemDIS).All other electronic charts areknown as ElectronicChart Systems (ECS).Following sections discuss the dif-controlstheprocessingof informationfromtheship'snavi-ferences betweenthesetwotypesofelectronicchartsgation sensors and theflowof information betweenvarioussystem components. It takes inputs from the vessel's naviga-An integrated bridge system may receive electroniction sensors.Electronic positioning information,contactchart datafrom the system manufacturerorfromtheappro-informationfromradar,andgyrocompassoutputs,forex-priategovernment agency.Themariner can also digitize anample,can be integrated withtheelectronic charttopresentexistingpaperchart if thesystem manufacturerprovidesathe complete navigation and tactical picturetotheconningdigitizer.Electronic charts can differentiate between and219
219 CHAPTER 14 ECDIS AND THE INTEGRATED BRIDGE INTRODUCTION 1400. Operating Concept Bridge watch officers have three main duties: Navigation • Watch officers process navigation information from several different sources. They take fix positions from satellite and hyperbolic receivers. They measure bearing lines and radar ranges to suitable NAVAIDS. They then plot this information on a paper chart. • After plotting the information on a chart, watch officers evaluate the navigation picture. They determine if the ship’s present position is a safe one. They project the ship’s position ahead and plan for future contingencies. The evaluation step is the most important step in the navigation process. Properly executing this step is a function of the watch officer’s skill and how well the ship’s actual navigation situation is represented on the chart. That representation, in turn, is a function of both plotter and sensor accuracy. Collision Avoidance • Watch officers evaluate the contact situation and calculate the closest points of approach (CPA’s) for various contacts. • Watch officers maneuver in accordance with the Rules of the Road to avoid close CPA’s and collisions. Ship Management • Watch officers conduct evolutions that are part of an individual ship’s routine. The integrated bridge is designed to reduce the time spent on navigation by eliminating manual data processing and providing the navigator with a display which aids him in quickly evaluating the navigation picture. Preliminary studies seem to indicate that time spent on navigation as a percentage of total watch officer duties drops significantly when using the integrated bridge. This does not necessarily lower the overall watch officer workload, but it does increase the percentage of time he can devote to ship management and collision avoidance. THE INTEGRATED BRIDGE 1401. System Components The term “integrated bridge” encompasses several possible combinations of equipment and software designed specifically for each individual vessel’s needs. Therefore, each integrated bridge system is different. This section introduces, in general terms, the major equipment likely to be found in an integrated bridge system. • Computer Processor and Network: This subsystem controls the processing of information from the ship’s navigation sensors and the flow of information between various system components. It takes inputs from the vessel’s navigation sensors. Electronic positioning information, contact information from radar, and gyro compass outputs, for example, can be integrated with the electronic chart to present the complete navigation and tactical picture to the conning officer. The system’s computer network processes the positioning information and controls the integrated bridge system’s display and control functions. • Chart Data Base: At the heart of any integrated bridge system lies an electronic chart. An electronic chart system meeting International Maritime Organization (IMO) specifications for complying with chart carrying requirements is an Electronic Chart Display and Information System (ECDIS). All other electronic charts are known as Electronic Chart Systems (ECS). Following sections discuss the differences between these two types of electronic charts. An integrated bridge system may receive electronic chart data from the system manufacturer or from the appropriate government agency. The mariner can also digitize an existing paper chart if the system manufacturer provides a digitizer. Electronic charts can differentiate between and
220ECDIS ANDTHEINTEGRATEDBRIDGEdisplay different types of data far better than conventionaloperatorcan select the course-up display as well.Eachtimecharts.Paper charts areusuallylimited tofour colors,andthe ship approaches the edge of the display, the screen willthey display all their data continuously.An electronic chartre-draw withthe ship centered or at the oppositeedge.can display several colors, and it can display onlythe dataAseparatemonitor,ora windowinthenavigationthe user needs.If theelectronicchart is partof an ECDISmonitor,can beusedfordisplay ofalpha-numericdata suchhowever, it mustalways display the minmum data requiredas course, speed, and cross-track error.It can also be usedbyIMO/IHO.Thedatabaseforatypical civilianelectronictodisplaysmall scalecharts of the areabeingnavigated,orchartcontainslayersconsistingofhydrography,aidstonav-to look at other areas while the main displayshows theigationobstructions,port facilities,shoreline,regulatoryship's current situation.boundaries and certaintopographicfeatures.Other layerssuch as communication networks,power grids,detailed: Planning Station: The navigator does his voyage plan-bathymetry,and radarreflectivity can alsobemadeavail-ning at this station.He calculates great circle coursesable.This allows theuserto customize his chart accordingplanned tracks, and waypoints.The navigator digitizes histohisparticular needs,something a paper chartcannotdo.charts, if required, at this planning station..Control System:Some integratedbridgesprovidea system.System Display: This unit displays the ship's position onthatautomaticallyadjusts course and speedtofollowaplannedanelectronic chartandprovides information onsensor statustrack.If the system is equipped with this feature, the navigationand ship's control systems.It displaysheading data andprocess isreducedto monitoring systemresponse and providingship's speed.Itprovides a station where the operator can in-operatoraction when requiredby eitherachangingtactical situ-put warning parameters such as minimum depth under theationorasystemcasualtykeelormaximumcrosstrackerror.Itplotstheship'spositionand itsposition inrelationtoapredetermined track:Radar:Radar for navigation and collision avoidance is in-There are two possible modes ofdisplay, relative andcluded in the integrated bridge.Since both thechartandtheradartrue. In the relative mode the ship remains fixed in the cen-process their data digitally,data transferbetween the two is pos-ter of the screen and the chart moves past it.This requires asible.The“picture"fromeitheronecanbe imposedontopofthelot ofcomputerpower,as all thescreendatamustbeupdat-ed and re-drawn at each fix.In truemode,the chartremainspicture of the other.This allows the navigatorto see an integrat-fixedandtheshipmovesacross it.Theoperatoralwayshased navigation and tactical displayand to avoid both navigationthe choice ofthe north-up display.On some equipment, thehazards and interfering contacts.ELECTRONICCHARTDISPLAYANDINFORMATIONSYSTEMThe unqualified use of the electronic chart in the inte-the chart since they are not separated in the data file.Rastergrated bridgedepends on the legal status of the electronicdata files tend to belarge,since a datapoint mustbe enteredchart system in use.TheIMOhas defined the Electronicforeverypictureelement (pixel)onthechartChart Display and Information System as the integratedVector chart data is organized into many separate files.It contains graphics programs to produce certain symbols,bridge system that complieswiththeup-to-date chartcarry-ing requirements of international law.TheElectroniclines,area colors,and otherchartelements.Theprogram-Nautical Chart (ENC) is the ship's electronic chart datamer can change individual elements in the file and tagbaseused inanECDIS system.TheENC is a subsetoftheelements withadditional data.Vectorfiles are smaller andElectronicChartDatabase(ECDB),the digital chart data-more versatile than raster files of the same area.The navi-base maintainedbythe national hydrographic authoritygator can selectively display vector data,adjusting theECDIS standards are still under development.Thisdisplayaccordingto hisneeds.CurrentIMO/IHO standardssection will discuss somebasicECDIS design criteriaforECDIS recognizeonlythevectorformatasadequate.Whether a digital chart system uses a raster or vector1402.DigitalChartData Formatsdata base, any change to that data base must come onlyfromthehydrographic office(HO)thatproduced theENCOne question in the development of ECDIS has beenCorrections from other sources affecting the data basewhether the nautical chart should be digitized in raster orshould be applied only as an overlay to the official datavectorformat.base.This protects the integrity of the official data base.Raster chartdata is a digitized"picture"ofa chart.All1403.DigitalChartDataTransferdata is in one layer and oneformat.The video displaysim-plyreproduces the picture from its digitized data file.WithThe IMO, in its performance standards for ECDIS, hasraster data, it is difficult to change individual elements of
220 ECDIS AND THE INTEGRATED BRIDGE display different types of data far better than conventional charts. Paper charts are usually limited to four colors, and they display all their data continuously. An electronic chart can display several colors, and it can display only the data the user needs. If the electronic chart is part of an ECDIS, however, it must always display the minmum data required by IMO/IHO. The database for a typical civilian electronic chart contains layers consisting of hydrography, aids to navigation, obstructions, port facilities, shoreline, regulatory boundaries and certain topographic features. Other layers such as communication networks, power grids, detailed bathymetry, and radar reflectivity can also be made available. This allows the user to customize his chart according to his particular needs, something a paper chart cannot do. • System Display: This unit displays the ship’s position on an electronic chart and provides information on sensor status and ship’s control systems. It displays heading data and ship’s speed. It provides a station where the operator can input warning parameters such as minimum depth under the keel or maximum cross track error. It plots the ship’s position and its position in relation to a predetermined track. There are two possible modes of display, relative and true. In the relative mode the ship remains fixed in the center of the screen and the chart moves past it. This requires a lot of computer power, as all the screen data must be updated and re-drawn at each fix. In true mode, the chart remains fixed and the ship moves across it. The operator always has the choice of the north-up display. On some equipment, the operator can select the course-up display as well. Each time the ship approaches the edge of the display, the screen will re-draw with the ship centered or at the opposite edge. A separate monitor, or a window in the navigation monitor, can be used for display of alpha-numeric data such as course, speed, and cross-track error. It can also be used to display small scale charts of the area being navigated, or to look at other areas while the main display shows the ship’s current situation. • Planning Station: The navigator does his voyage planning at this station. He calculates great circle courses, planned tracks, and waypoints. The navigator digitizes his charts, if required, at this planning station. • Control System: Some integrated bridges provide a system that automatically adjusts course and speed to follow a planned track. If the system is equipped with this feature, the navigation process is reduced to monitoring system response and providing operator action when required by either a changing tactical situation or a system casualty. • Radar: Radar for navigation and collision avoidance is included in the integrated bridge. Since both the chart and the radar process their data digitally, data transfer between the two is possible. The “picture” from either one can be imposed on top of the picture of the other. This allows the navigator to see an integrated navigation and tactical display and to avoid both navigation hazards and interfering contacts. ELECTRONIC CHART DISPLAY AND INFORMATION SYSTEM The unqualified use of the electronic chart in the integrated bridge depends on the legal status of the electronic chart system in use. The IMO has defined the Electronic Chart Display and Information System as the integrated bridge system that complies with the up-to-date chart carrying requirements of international law. The Electronic Nautical Chart (ENC) is the ship’s electronic chart data base used in an ECDIS system. The ENC is a subset of the Electronic Chart Database (ECDB), the digital chart database maintained by the national hydrographic authority. ECDIS standards are still under development. This section will discuss some basic ECDIS design criteria. 1402. Digital Chart Data Formats One question in the development of ECDIS has been whether the nautical chart should be digitized in raster or vector format. Raster chart data is a digitized “picture” of a chart. All data is in one layer and one format. The video display simply reproduces the picture from its digitized data file. With raster data, it is difficult to change individual elements of the chart since they are not separated in the data file. Raster data files tend to be large, since a data point must be entered for every picture element (pixel) on the chart. Vector chart data is organized into many separate files. It contains graphics programs to produce certain symbols, lines, area colors, and other chart elements. The programmer can change individual elements in the file and tag elements with additional data. Vector files are smaller and more versatile than raster files of the same area. The navigator can selectively display vector data, adjusting the display according to his needs. Current IMO/IHO standards for ECDIS recognize only the vector format as adequate. Whether a digital chart system uses a raster or vector data base, any change to that data base must come only from the hydrographic office (HO) that produced the ENC. Corrections from other sources affecting the data base should be applied only as an overlay to the official data base. This protects the integrity of the official data base. 1403. Digital Chart Data Transfer The IMO, in its performance standards for ECDIS, has
221ECDISANDTHEINTEGRATEDBRIDGEmandated that individual national hydrographic offices will:timedoesnotallowforanimmediateconversionofsupplyofficial ENC dataforECDIS use.Apreliminarythe English units to their metric equivalents.datatransfer standard,known asDX90, has beenproposedwithin theIHO,IHO is debating the utilityof this standard.Height: Meters (preferred) or feet.Regardless of the transfer standard recommended, each na-tional hydrographic office that produces a data base will·Distance: Nautical miles and decimal miles, ordecidewhattransferstandarditwillusemeters.To ensure the reliability of the data, the ECDIS mustnotallowdatafrom an unofficial source to erase,overwrite,. Speed: Knots and decimal knots.ormodifyHO supplied data.1406.ECDISPriorityLayers1404.ECDIS Warnings And AlarmsECDIS requires data layers to establish a priority ofSince the ECDIS is a “"smart" system which combinesdata displayed.The minimum number of information cate-several different functions into one computerized system, it isgories required and their relative priority from the highestpossibleto program itto sound alarmsordisplay warningsto lowest priority,are listed below:when certain parameters are met or exceeded. This helps thenavigator to monitor close navigation hazards.IMO standards·ECDIS Warnings and Messages.require that certain alarms be available on theECDIS.Amongthese are::Hydrographic Office Data.1.Deviating from a planned route·Notice to Mariners Information.2.Chartonadifferentgeodetic datumfromtheposi-tioning system.Hydrographic Office Cautions.Approach to waypoints and other critical points.3.4.Exceeding cross-track limits..Hydrographic Office Color-Fill Area Data.5.Chart data displayed overscale (larger scale thanoriginally digitized)..Hydrographic Office On Demand Data.Larger scale chart available6.Failureofthepositioningsystem:Radar Information8.Vessel crossingsafetycontour.. User's Data9.System malfunction or failure.: Manufacturer's DataAlarms consist of audible and visible warnings.The nav-igator may determine some setpoints.For example, he may·User'sColor-Fill Area Datadesignatea safetydepthcontour orsetamaximumallowedcross-track error.Operational details varyfromonesystemtoanother,but all ECDIS will havethebasic alarm capabilities·Manufacturer's Color-Fill Area Data.noted.Thenavigator isresponsibleforbecomingfamiliar withthe system aboard his own ship and using it effectivelyIMO standards for ECDIS will require that the operatorbeabletodeselect theradarpicturefromthe chart withmin-1405.ECDISUnitsimum operator action for fast“uncluttering"of the chartpresentation.Thefollowing units ofmeasure will appear on the EC-DIS chart display:1407.ECDISCalculationRequirements.Position: Latitude and Longitude will be shown inAsaminimum,anECDISsystemmustbeabletoper-degrees,minutes,and decimal minutes, normalform thefollowing calculations:lybased onWGS-84datum.Geographical coordinates todisplay coordinates,and.Depth:Depth will be indicated in meters and decidisplay coordinatestogeographical coordinates.meters.Fathoms and feet may be used as aninterimmeasureonly::Transformationfromlocal datumtoWGS-84. when existing chart udata is held in those units only,.when there is an urgent need for an ENC of the.True distance and azimuth between two geographicalapplicablearea,andpositions
ECDIS AND THE INTEGRATED BRIDGE 221 mandated that individual national hydrographic offices will supply official ENC data for ECDIS use. A preliminary data transfer standard, known as DX 90, has been proposed within the IHO; IHO is debating the utility of this standard. Regardless of the transfer standard recommended, each national hydrographic office that produces a data base will decide what transfer standard it will use. To ensure the reliability of the data, the ECDIS must not allow data from an unofficial source to erase, overwrite, or modify HO supplied data. 1404. ECDIS Warnings And Alarms Since the ECDIS is a “smart” system which combines several different functions into one computerized system, it is possible to program it to sound alarms or display warnings when certain parameters are met or exceeded. This helps the navigator to monitor close navigation hazards. IMO standards require that certain alarms be available on the ECDIS. Among these are: 1. Deviating from a planned route. 2. Chart on a different geodetic datum from the positioning system. 3. Approach to waypoints and other critical points. 4. Exceeding cross-track limits. 5. Chart data displayed overscale (larger scale than originally digitized). 6. Larger scale chart available. 7. Failure of the positioning system. 8. Vessel crossing safety contour. 9. System malfunction or failure. Alarms consist of audible and visible warnings. The navigator may determine some setpoints. For example, he may designate a safety depth contour or set a maximum allowed cross-track error. Operational details vary from one system to another, but all ECDIS will have the basic alarm capabilities noted. The navigator is responsible for becoming familiar with the system aboard his own ship and using it effectively. 1405. ECDIS Units The following units of measure will appear on the ECDIS chart display: • Position: Latitude and Longitude will be shown in degrees, minutes, and decimal minutes, normally based on WGS-84 datum. • Depth: Depth will be indicated in meters and decimeters. Fathoms and feet may be used as an interim measure only: • when existing chart udata is held in those units only, • when there is an urgent need for an ENC of the applicable area, and • time does not allow for an immediate conversion of the English units to their metric equivalents. • Height: Meters (preferred) or feet. • Distance: Nautical miles and decimal miles, or meters. • Speed: Knots and decimal knots. 1406. ECDIS Priority Layers ECDIS requires data layers to establish a priority of data displayed. The minimum number of information categories required and their relative priority from the highest to lowest priority, are listed below: • ECDIS Warnings and Messages. • Hydrographic Office Data. • Notice to Mariners Information. • Hydrographic Office Cautions. • Hydrographic Office Color-Fill Area Data. • Hydrographic Office On Demand Data. • Radar Information. • User’s Data. • Manufacturer’s Data. • User’s Color-Fill Area Data. • Manufacturer’s Color-Fill Area Data. IMO standards for ECDIS will require that the operator be able to deselect the radar picture from the chart with minimum operator action for fast “uncluttering” of the chart presentation. 1407. ECDIS Calculation Requirements As a minimum, an ECDIS system must be able to perform the following calculations: • Geographical coordinates to display coordinates, and display coordinates to geographical coordinates. • Transformation from local datum to WGS-84. • True distance and azimuth between two geographical positions
222ECDIS AND THEINTEGRATEDBRIDGE·Projection calculations such as great circle and:Geographic position from a known position givendistance and azimuth.rhumblinecoursesanddistancesELECTRONICCHARTSYSTEMS1408.ECSAndECDISand control systems to create afully integrated bridgeThe uncertainty surrounding the final ECDIS standardElectronicChart Systems (ECS)arethosedigital charthasnotlessenedthemarinecommunity'sdemandtoexploitdisplaysystemsthatdonotmeettheIMOrequirementsforthepotential of this revolutionarytechnology.ECDIS.Until an ECDIS standard is approved and a particu-Oneconsequenceofthisdemandhasbeenthatsomelar ECSmeets that standard, noECS can be classified as annational hydrographic offices areproducing official digitalECDIS.The practical consequence ofthis distinction is thatraster charts for use in electronic charting systems.In addi-anECScannotbeused toreplaceapapercharttion, a number of commercial companies have beenLegal requirements notwithstanding,several companieslicensed to digitizethepaper charts of various national hy-drographic offices. However, these are not the data basesareproducing verysophisticated integrated bridge systemsbased on electronic chart systems.Theseintegrated bridgesenvisioned bytheIMO standardRemember that ECDIS is a system. The electroniccombine accurate electronic positioning sensors withelec-tronic chartpresentations to producea videorepresentationchart data base is only a subset of this system. Thereforeof a chart which displays and updates the ship's charted po-even thoughelectronic charts come from a national hydro-sition atfrequent intervals.Electronic charts can also displaygraphic office orfrom official charts,the integrated bridgesystem in which the chart is used maynot meet the ECDIStracklines,cross-trackerror,and otheroperationaldataThesesystemshavethe potential to integrate radar systemssystem requirements.NAVIGATIONSENSORSYSTEMINTERFACE(NAVSSI)1409.SystemDescriptioncome from GPS, Loran, inertial navigation systems, gyrocompass,and speedlog.ThebridgedisplayconsistsofaDMA'sVectorProductFormat(VPF)DigitalNauticalmonitor and control panel, while the RTS is mounted belowCharts (DNC's)are used in conjunction with theNavy'sdecks.ENC's are contained in the Display and Controlversion of the integrated bridge:the Navigation SensorSubsystem(DCS)typicallymounted inthechartroomwithSystem Interface (NAVSSI).NAVSSI is being developeda monitor on the bridge.This is unlike many current com-tofulfill three important functions:mercial systems whichhaveall hardwareand software in asingleunitonthebridge.AseparateNAVSSIsoftware.Navigation Safety:NAVsSI distributes real timepackage supports operator interface,waypointcapability,navigation data to the navigation team members tocollision and grounding avoidance features, and other as-pectsofanECDISensurenavigationsafetyFigure 1410 illustrates a basic block diagram of the.Weapons System Support: NAVSSI provides guid-NAVSSI system.TheRTStakes inputsfromthe inertialnavigators (WSN-5's), the GPS PPS (WRN-6), the gyroance initializationfor usebyweapons systems.compass,theEMLog,and theSRN-25.TheSRN-25out-.Battlegroup Planning: NAVSSI provides a work-puts GPS sPS, Transit SATNAV, and Omega positions.sation forbattlegroup planningThe RTS distributes navigation information to thevarioustactical applications requiring navigation input, and itThenavigationfunction ofNAVSSI,therefore,isonlycommunicatesviaafiberoptic networkwiththeDCSThe DCS exchanges information with the Navigator'soneof severalfunctions accomplished by the system.Thenavigational portionof NAVSSI is being designedtocom-Workstation.plywiththeIMO/IHOECDIS standardsforcontentand1410.TheDigital NauticalChartfunctionThe heart of NAVSSI is the Real Time SubsystemNAVSSI uses the Digital Nautical Chart(DNC)as its(RTS).TheRTSreceives,processes anddistributesnavigational datatothenavigation display,weapons systems,andchart database.TheDNC is inVectorProductFormat andothernetworked vessels.This ensures that all elements ofais based on the contentsof thetraditionalpaperharbor,ap-proach,and coastal charts producedbyDMA and NOS.battle group have the same navigational picture.Inputs
222 ECDIS AND THE INTEGRATED BRIDGE • Geographic position from a known position given distance and azimuth. • Projection calculations such as great circle and rhumb line courses and distances. ELECTRONIC CHART SYSTEMS 1408. ECS And ECDIS Electronic Chart Systems (ECS) are those digital chart display systems that do not meet the IMO requirements for ECDIS. Until an ECDIS standard is approved and a particular ECS meets that standard, no ECS can be classified as an ECDIS. The practical consequence of this distinction is that an ECS cannot be used to replace a paper chart. Legal requirements notwithstanding, several companies are producing very sophisticated integrated bridge systems based on electronic chart systems. These integrated bridges combine accurate electronic positioning sensors with electronic chart presentations to produce a video representation of a chart which displays and updates the ship’s charted position at frequent intervals. Electronic charts can also display tracklines, cross-track error, and other operational data. These systems have the potential to integrate radar systems and control systems to create a fully integrated bridge. The uncertainty surrounding the final ECDIS standard has not lessened the marine community’s demand to exploit the potential of this revolutionary technology. One consequence of this demand has been that some national hydrographic offices are producing official digital raster charts for use in electronic charting systems. In addition, a number of commercial companies have been licensed to digitize the paper charts of various national hydrographic offices. However, these are not the data bases envisioned by the IMO standard. Remember that ECDIS is a system. The electronic chart data base is only a subset of this system. Therefore, even though electronic charts come from a national hydrographic office or from official charts, the integrated bridge system in which the chart is used may not meet the ECDIS system requirements. NAVIGATION SENSOR SYSTEM INTERFACE (NAVSSI) 1409. System Description DMA’s Vector Product Format (VPF) Digital Nautical Charts (DNC’s) are used in conjunction with the Navy’s version of the integrated bridge: the Navigation Sensor System Interface (NAVSSI). NAVSSI is being developed to fulfill three important functions: • Navigation Safety: NAVSSI distributes real time navigation data to the navigation team members to ensure navigation safety. • Weapons System Support: NAVSSI provides guidance initialization for use by weapons systems. • Battlegroup Planning: NAVSSI provides a worksation for battlegroup planning. The navigation function of NAVSSI, therefore, is only one of several functions accomplished by the system. The navigational portion of NAVSSI is being designed to comply with the IMO/IHO ECDIS standards for content and function. The heart of NAVSSI is the Real Time Subsystem (RTS). The RTS receives, processes and distributes navigational data to the navigation display, weapons systems, and other networked vessels. This ensures that all elements of a battle group have the same navigational picture. Inputs come from GPS, Loran, inertial navigation systems, gyrocompass, and speed log. The bridge display consists of a monitor and control panel, while the RTS is mounted below decks. ENC’s are contained in the Display and Control Subsystem (DCS) typically mounted in the chartroom with a monitor on the bridge. This is unlike many current commercial systems which have all hardware and software in a single unit on the bridge. A separate NAVSSI software package supports operator interface, waypoint capability, collision and grounding avoidance features, and other aspects of an ECDIS. Figure 1410 illustrates a basic block diagram of the NAVSSI system. The RTS takes inputs from the inertial navigators (WSN-5’s), the GPS PPS (WRN-6), the gyro compass, the EM Log, and the SRN-25. The SRN-25 outputs GPS SPS, Transit SATNAV, and Omega positions. The RTS distributes navigation information to the various tactical applications requiring navigation input, and it communicates via a fiber optic network with the DCS. The DCS exchanges information with the Navigator’s Workstation. 1410. The Digital Nautical Chart NAVSSI uses the Digital Nautical Chart (DNC) as its chart database. The DNC is in Vector Product Format and is based on the contents of the traditional paper harbor, approach, and coastal charts produced by DMA and NOS
223ECDISANDTHEINTEGRATEDBRIDGEAN/WRN-6#2#1GyroEMLogAN/SRN-25AN/WSN-5AN/WSN-5Display andETHERNETReal Time SubsystemControlSubsystem(DCS)(I/OProcessor)(DTC-2Computer)--NAVSSISystemNavigator'sWorkstation (NWS)1OutboardJOTSTomahawkFigure 1410. Block diagram ofNAVSSI.Horizontal datum is WGS 84 (NAD 83 in the U. S. ischarts,and 3oX 3ofor general charts.The data now con-tained on as many as 4000 conventional charts willequivalent).There are three vertical datums.Topographicfeatures are referenced to Mean Sea Level, and the shoreeventuallybecontained onasfewas30CD's.line is referenced to Mean High Water. Hydrography is ref-1411.Correcting The Digital Nautical Charterenced to a low water level suitable for the region. Allmeasurementsaremetric.DNC data is layered together into 12 related feature classes:There are currentlythree proposed methodsfor cor-recting the DNC data base: Interactive Entry, Semi-Cultural LandmarksAutomatic Entry,andFullyAutomatic Entry.:Earth Cover:InlandWaterwaysInteractive Entry: This method requires the interac-·Relieftive application of the textual Notice to Mariners.The: Landcoveroperator determines the corectionsfrom theNotice.Port FacilitiesThen, using a toolkit, he selects the symbol appropriate:Aids to Navigationtothe correction required,identifies the locationof the.Obstructionssymbol,andadds theappropriatetextual information·Hydrographyidentifying the nature ofthecorrection.This method of:Environmentcorrection is labor intensiveand subjectto operator er-. Maritime Limiting Lines (channels, demarcationror.It also clutters the screen display because it can belines,anchorages,etc.)applied only as an overlay to the ENC data..Data QualitySemi-Automatic Entry:This method requires the op-Content is generally the same as on a paper chart. Theerator to enter the correction data furnished in correctdata is stored in libraries; each library represents a differ-digital format by the originating hydrographic officeent level of detail.The libraries are then stored on CDintothe systemviaelectronic medium(amodemorROM and organized as tiles accordingto theWorld Geofloppy disc,for example).TheECDIS thenprocessesdetic Reference System(GEOREF)tiling scheme.Tilethese corrections automaticallyand displays an updat-sizesare15'X15'forharborcharts,30'X30'forapproached chartwiththe changed data indistinguishablefrom
ECDIS AND THE INTEGRATED BRIDGE 223 Horizontal datum is WGS 84 (NAD 83 in the U. S. is equivalent). There are three vertical datums. Topographic features are referenced to Mean Sea Level, and the shore line is referenced to Mean High Water. Hydrography is referenced to a low water level suitable for the region. All measurements are metric. DNC data is layered together into 12 related feature classes: • Cultural Landmarks • Earth Cover • Inland Waterways • Relief • Landcover • Port Facilities • Aids to Navigation • Obstructions • Hydrography • Environment • Maritime Limiting Lines (channels, demarcation lines, anchorages, etc.) • Data Quality Content is generally the same as on a paper chart. The data is stored in libraries; each library represents a different level of detail. The libraries are then stored on CDROM and organized as tiles according to the World Geodetic Reference System (GEOREF) tiling scheme. Tile sizes are 15' X 15' for harbor charts, 30' X 30' for approach charts, and 3° X 3° for general charts. The data now contained on as many as 4000 conventional charts will eventually be contained on as few as 30 CD’s. 1411. Correcting The Digital Nautical Chart There are currently three proposed methods for correcting the DNC data base: Interactive Entry, SemiAutomatic Entry, and Fully Automatic Entry. Interactive Entry: This method requires the interactive application of the textual Notice to Mariners. The operator determines the corrections from the Notice. Then, using a toolkit, he selects the symbol appropriate to the correction required, identifies the location of the symbol, and adds the appropriate textual information identifying the nature of the correction. This method of correction is labor intensive and subject to operator error. It also clutters the screen display because it can be applied only as an overlay to the ENC data. Semi-Automatic Entry: This method requires the operator to enter the correction data furnished in correct digital format by the originating hydrographic office into the system via electronic medium (a modem or floppy disc, for example). The ECDIS then processes these corrections automatically and displays an updated chart with the changed data indistinguishable from Figure 1410. Block diagram of NAVSSI
224ECDISANDTHEINTEGRATEDBRIDGElink to receive the official digital update and input it intotheremainingoriginal databasethe ECDIS.This process is completely independent ofFully Automatic Entry:The fully automatic method ofany operator interface. Internal ECDIS processing is thecorrectionentryallowsforadirecttelecommunicationssameasthatforsemi-automaticupdatingofthedatabaseCONCLUSIONThe emergenceof extremelyaccurateelectronicposi-some legal, somebureaucratic,and sometechnical.Untiltioning systems coupled with the technology to produce anthose hurdles are overcome,electronic charting will be in aelectronic chart is effecting a revolution in navigation.transitional state, useful as a backup to traditional tech-When fully mature, this technology will replace the paperniques, but insufficientto replacethem.Howthis transitioncharts andplottinginstruments usedby navigators sincetheperiod will play out and the final form of the internationallybeginning of sea exploration. There are several hurdles torecognized ECDIS system are subjects for the next editionovercomeintheprocessoffull replacementofpapercharts,ofTheAmericanPracticalNavigator
224 ECDIS AND THE INTEGRATED BRIDGE the remaining original data base. Fully Automatic Entry: The fully automatic method of correction entry allows for a direct telecommunications link to receive the official digital update and input it into the ECDIS. This process is completely independent of any operator interface. Internal ECDIS processing is the same as that for semi-automatic updating of the data base. CONCLUSION The emergence of extremely accurate electronic positioning systems coupled with the technology to produce an electronic chart is effecting a revolution in navigation. When fully mature, this technology will replace the paper charts and plotting instruments used by navigators since the beginning of sea exploration. There are several hurdles to overcome in the process of full replacement of paper charts, some legal, some bureaucratic, and some technical. Until those hurdles are overcome, electronic charting will be in a transitional state, useful as a backup to traditional techniques, but insufficient to replace them. How this transition period will play out and the final form of the internationally recognized ECDIS system are subjects for the next edition of The American Practical Navigator