GPS导航系统在工程机械中的应用.docx
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GPS导航系统在工程机械中的应用.docx
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GPS导航系统在工程机械中的应用
AdvancesinBuildingTechnology,Volume2
M.Anson,J.M.KoandE.S.S.Lam(Eds.)
©2002ElsevierScienceLtd.Allrightsreserved
GPSNAVIGATIONANDGUIDANCESYSTEMSFOR
CONSTRUCTIONINDUSTRY
GuntherRetscherandEsmondMok
ABSTRACT
NewapplicationsfortheuseofGPShaveemergedespeciallyinconstructionindustryinrecentyears.Theapplicationsarerangingfromnavigationoftrucksinfleetmanagement,theguidanceofconstructionmachinestoprecisesurveying,settingoutandmonitoringofengineeringstructures.TherebyGPScanbeemployedinmanydifferentmodeswherethesuitablemethodisselecteddependingontheaccuracyrequirementsforpositiondetermination.Mostoftheseapplicationsrequirealsothepossibilityforcontinuouspositiondeterminationinreal-time.Ifthisisthecase,nowadaysmodernreal-timekinematicGPS(RTK-GPS)canbeemployed.Theuseofthesemodernsurveyingandpositioningtechniquesfacilitatesalsothedevelopmentofnewmachineryandsystemprocessesinconstructionindustry.Especiallyfortheguidanceofconstructionmachines,systemshavebeendevelopedtoincreasetheproductivityofconstructionworks.Commercialsystemsareavailablenowadaysfromseveralcompanies,e.g.fortheguidanceofgraders,dozersandcaterpillars.Ingeneral,thesystemsuse3-Dsurveyingsystemsforpositiondeterminationmostlyincombinationwithothersensors.
Followingabriefdescriptionofsatellitepositioningmodes,theirmajorapplicationsinconstructionindustrywillbehighlightedandcommonfeaturesofmodern3-DmachineguidancesystemsbasedonRTK-GPSwillbeoutlinedinthispaper.Finallythe3-Dmachineguidancesystemsarecomparedwithcommonconventionalsystemsandtheiradvantagessummarized.
KEYWORDS
GPS,SatellitePositioning,Navigation,FleetManagement,MachineGuidance,ConstructionMachines,3-DMachineGuidanceSystems.
1INTRODUCTION
Whetherthegivenapplicationisingeneralconstruction,earthmovingorcivilengineering,nowadaysadvancedsurveyingtechniquesusinglasers,totalstationsandGPSpositioningsolutionsandsoftwareareavailablethatcanprovidemorecontroloverthejobtaskandsite.Forsitepreparation,powerfulsoftwarefordesignandestimatingtakeoffaswellasacompletelineofmachinecontrolsystemsforthesmallestskidsteertothelargestbulldozercanbeemployed.Therebymodernmachinecontrolsystemsuseavarietyoftechnologies,eitherincombinationoralone,includinglaser,GPSsystems,totalstation,sonicorlasertracersandsoftware.Usingadvancedmachinecontrolsystemsoperatorshavetheinformationtheyneedinthecab,allowingthemtosignificantlyincreaseproductivity,reducematerialoveragesandworkwithgreaterprecision.Startingfromashortdescriptionoftheprincipleofoperationofmodernsatellitepositioningandnavigationmethods,theuseofGPSinconstructionindustryandmachineguidancewillbedescribedmoreindetailinthispaper.
2GPSPOSITIONINGANDNAVIGATION
Satellitepositioningsystemshavebeendevelopedtoprovidethepossibilityforcontinuouspositiondeterminationworldwide.Newsystemsarecurrentlyunderdevelopmentoratthestageoflaunchingtheirsatellitesintoorbit.Allofthemhaveincommon,thattheyweredevelopedfollowingtheconceptofthesuccessfulU.S.NAVSTAR-GPS(NavigationSystemwithTimeandRanging-GlobalPositioningSystem).Thedevelopmentofthissystemstartedalreadyinthe1970'sbytheDepartmentofDefence(DoD)oftheU.S.A.Thereforethesystemwasprimarilyinstalledformilitarynavigation.BesidestheU.S.A.,alsotheformerSovietUnionStatesdevelopedasimilarsystem,theso-calledGLONASS(Russian'sGlobalNavigationSatelliteSystem).Inthe90's,theintegrationofGPSandGLONASSwasonesteptowardsafutureGlobalNavigationSatelliteSystems(GNSS).StrategicgoalsoftheGNSSweretocreateasystemthatisindependentfromanymilitaryornationalcontrol,toguaranteethecontinuityofserviceoveracertaintimeperiod,andtoofferanimprovedservicecomparedtoGPSwhichisaffordable.MainlybecauseofmilitaryreasonsandthedisagreementoftheU.S.governmenttoallowinternationalcontrolforGPS,theEuropeancommunityalsostartedtodevelopanownglobalsatellitenavigationsystemattheendof'lastcentury.ThissystemiscalledGALILEOandshouldbefullyoperableattheendof2008.
2.1BasicConceptofSatellitePositioning
Astheconceptofsatellitepositioningsystemsisverysimilaritwillbeeasytounderstandtheconceptofotherswiththeknowledgeoftheconceptofonesystem.Thedesignconceptofasatellitepositioningsystemhastofulfilthefollowingrequirements:
Thesystemmustguarantee3-Dpositioningdeterminationanywhereintheworld,atanytimeandduringanyweatherconditionwiththespecifiedpositioningaccuracy.Inadditiontopositiondetermination,formanyapplicationsalsothedeterminationofthevelocityandaccelerationofthemovingreceivermustbepossible.
Ingeneral,thesatellitepositioningsystemsconsistsofthreesegments,i.e.,thespacesegment(satellitesinorbit),thegroundcontrolsegment(monitoringstationsandmastercontrolstation)andtheusersegment(receiverandantenna).Foridentificationanddistancemeasurements,thesatellitesbroadcastcodesequenceswhicharemodulatedoncarrierphasesignals.InthecaseofGPS,twosinusoidalcarrierphasesignals,L1andL2
andtwoPRN(pseudo-randomnoise)codes,thepreciseP-codeandtheC/A-code
,arebroadcasted.ForthefuturegenerationofGPSsatellites,itisplannedtoaddathirdcivilianandanothermilitaryfrequency.Thesatelliteorbitsaredeterminedbyanetworkofmonitorstationsaroundtheworld.Theseso-calledbroadcastephemerisarethentransferredtotheuserfromthesatellitesinthenavigationmessagetoobtainreal-timepositiondetermination.Theusersegmentcanbebroadlyclassifiedintousersformilitaryandcivilianapplications.TherearevarioustypesofGPSreceiversavailableonthemarkettosuitdifferentapplicationssuchassurveyingandmapping,vehiclenavigationandrecreation.Furtherinformationabouttheirprinciplecanbefoundinbooksaboutsatellitepositioning,e.g.(Hofrnann-Wellenhofet.al,1992;Leick,1995;Wells,1986;Seeber,1993;Mok&Retscher,2000).
2.2ObservationTypesandPositioningModes
Positiondeterminationisdonebydistanceorrangemeasurements.Dependingonthetypeofobservationused,pseudorangemeasurementswiththecodephases(P-codeorC/A-code)orcarrierphasemeasurements(signalLlor/andL2)canbecarriedout.Therebypositioningaccuraciesintherangeof0.3to40mcanbeobtainedusingcodeobservations.Higheraccuracypositiondeterminationuptothecentimetrelevel,however,canonlybeachievedusingcarrierphasemeasurements.TheaccuracyspectrumofdifferentmethodsiscomparedgraphicallyinFig.1.Ascanbeseen,differentsatellitepositioningtechniquesofferawiderangeofpositioningaccuracies.Afterdistinguishingbetweencodeandphaseobservations,themethodscanbecategorisedintoabsoluteandrelativepositioningtechniques.Thetermabsoluteorsingle-pointpositioningisusedtodescribepositioningtechniquesusingonlyonereceiverinstand-alonemode.Thistechniqueisusuallyappliedfornavigation.Forrelativepositioning,however,atleasttworeceiversarerequired.Duetotheuseofdifferencingtechniques,thepositioningaccuracycanbeincreasedforsimultaneousobservationsoftworeceiverstoatleastfoursatellites.Thesetechniquesareusuallyappliedinsurveying,formappingapplicationsandalsoforprecisenavigation.
ThesignalsLlandL2areelectromagneticwavesintheL-bandwithfrequenciesof1575.42MHzand1227.60MHz.
P-codestandsforPrecisecodeandC/A-codeforCoarse/Acquisitioncode.ThePRNcodeisarandomsignalof‘+l’and‘-1’codesequences.
SPSstandsforStandardPositioningServiceusingtheC/ACodeandPPSforPrecisePositioningServicewiththeP-code.
2.3GPSPositioningModesforSurveying
Positioningmethodsusedinsurveyingareusuallyrelativepositioningtechniqueswithcarrierphaseobservationstoachieveahighlevelofprecision.Ingeneral,itcanbedistinguishedbetweenstaticpositioning,rapid(orfast)staticpositioning,stop-and-go,reoccupationandkinematicpositioning.Themodesdiffermainlyintheirobservationtimeandwhetherthereceiversarestaticormovingthroughouttheentireobservationperiod.Thehighestpositioningaccuracycanbeobtainedusingthestaticpositioningtechnique.Inthiscase,bothreceiversarestationaryontheirpointsoveracertainperiodoftime.Thelengthoftheobservationperioddependsonthenumberofsatellites,theprecisionrequirements,thelengthoftheline,thetypeofreceiver(singleLlordualfrequencyreceiverLlandL2),andtheatmosphericconditions.Staticobservationsaretakenoveratimespanof30minutesuptoseveralhoursandrapidstaticobservationswithinafewminutesupto20minutes.Ifmorethantworeceiversareused,thestaticmethodcanbeemployedformanysurveyapplications,especiallyfortheestablishmentofcontrolnetworksveryeconomically.Satellitepositioningtechniqueshavethereforenearlyreplacedconventionalsurveyingtechniquesforthistypeofapplication.Thesurveyworkisveryeasyandtheprocessingoftheresultsisusuallydoneinpostmission.Thesetechniqueisemployede.g.fortheestablishmentofcontrolpointsforengineeringprojects(constructionofatunnelorbridge).Fortherapidstaticorstop-and-goobservations,thelimitedfactoristheshortobservationtimeofafewminutesoronlyseconds.Duetorecentde
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