摄影测量和激光扫描的比较测绘专业英语翻译英doc.docx

摄影测量和激光扫描的比较测绘专业英语翻译英doc.docx

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摄影测量和激光扫描的比较测绘专业英语翻译英doc

Acomparisonbetweenphotogrammetryandlaserscanning

EmmanuelP.Baltsavias

InstituteofGeodesyandPhotogrammetry,SwissFederalInstituteofTechnology,ETH-Hoenggerberg,CH-8093Zurich,Switzerland

Received22October1998;accepted17March1999

Abstract

Acomparisonbetweendataacquisitionandprocessingfrompassiveopticalsensorsandairbornelaserscanningispresented.Ashortoverviewandthemajordifferencesbetweenthetwotechnologiesareoutlined.Advantagesanddisadvantageswithrespecttovariousaspectsarediscussed,likesensors,platforms,flightplanning,dataacquisitionconditions,imaging,objectreflectance,automation,accuracy,flexibilityandmaturity,productiontimeandcosts.AmoredetailedcomparisonispresentedwithrespecttoDTMandDSMgeneration.Strengthsoflaserscanningwithrespecttocertainapplicationsareoutlined.Althoughairbornelaserscanningcompetestoacertainextentwithphotogrammetryandwillreplaceitincertaincases,thetwotechnologiesarefairlycomplementaryandtheirintegrationcanleadtomoreaccurateandcompleteproducts,andopenupnewareasofapplication.q1999ElsevierScienceB.V.Allrightsreserved.

Keywords:

digitalandanalyticalphotogrammetry;airbornelaserscanning;comparison;DTMgeneration;applications

1.Introduction

Thecomparisonbelowwillberestrictedtoairbornesystems,andranginglasersystemsonly,i.e.,excludingairborne-basedprobinglidarthatisusedmainlyforenvironmentalandotherthematicapplica-tions.Differentexperimentalsystems（seeBalt-savias,1999b）,developedmainlybyNASA,aswellasALSsystemswithdualfrequenciesforbathymetric/hydrographicapplications,willnotbetreatedhere.Thefirstgroupshowssomeinterestingtechnologicaldevelopmentsandnewareasofapplication,whiletheapplicationdomainofthesecondgroupcaninprinciplenotbetreatedbyotheropticalsensors.Inphotogrammetry,bothanalogueanddigitalsensors,andanalyticalaswellasdigitalphotogrammetricsystemswillbeincluded.

1.1.Shortoverview

Photogrammetryisbasedonprocessingofimages,withmainproducts:

DTMs,DSMs,orthoimages,2Dand3Dreconstructionandclassificationofobjectsformappingorthematicapplications,andvisualisation（maps,3Dviews,animationandsimulation）.Processingoffilmsisusuallymadebyana-lyticalplotters（inuseforabout20years）,whiledigitaldataareprocessedbyDigitalPhotogrammetricSystems（DPS）.whichareinuseforabout7–9years.Theprocessingalgorithmsarebeingcontinuouslydeveloped.Photogrammetrictheoriescancountonalonghistoryofdevelopmentsforoveracentury.Intensiveresearchhasbeenconductedforthelast20yearsfortheautomationofinformationextractionfromdigitalimages,basedonimageanalysismethods.

Laser,oneofthemostimportanttechnologicaldevelopmentsofthiscentury,wasintroducedinourcommunitymainlythroughtheresearchactivitiesoftheInstituteofPhotogrammetry（Prof.F.Acker-mann）,UniversityofStuttgart,in1988.Duringthelast2–3years,theinterestinairbornelaserscanning（ALS）hasstronglyincreased.Currently,aboutfivecompaniessell（orplantosellshortly）ALSsystems,whileworldwideabout35companiesofferservices,andabouthalfofthemwithcustom-madesystems.AlmostallsystemsmakeuseofGPSandINSforsensororientation.Thelaserfrequencyisinthe500–1500nmrange,withtypicalvaluesof1040–1060nm.Airbornelaserrangingsystemstypicallyuseopticallypumped（oftenwithlaserdiodes）solid-statelaserswithshortpulses（ca.10ns）ofmediumtohighpowerandabeamdivergenceofca.1mrad.Somesystemsallowtherecordingofmultipleechoesfromonelaserpulse,e.g.,firstandlast,orevenadditionalonesinregularintervalsin-between.Someofthesystemsdelivernotjustrangebutalsointensityinformation,wherebythelatterhasbeenusedverylittleuptonow.Manysystemsprovideadditionalon-boardstandardvideoordigitalcameras;theseare,however,usuallyonlylooselyintegratedwiththeALSandGPS/INSsystems.Integrationwithphotogrammetriccameras,multispectralsensors,SAR,etc.hasremaineduptonowonalimitedlevel.ALScanbeperformedfromhelicopters,fixed-wingaircraftsorboth.Flyingheightscanvaryfrom20to6000m,whiletypicalvaluesareintherangeof200–1000m.Theprocessingoftherawdataisusuallydonebytheservicefirmswithpartlyunknownalgorithmsandprocedures,especiallyforthemorecomplicatedandlaterprocessinginvolvingpointfilteringandclassification,whiletherearesomecommercialpackagesthatallowGPS/INSprocessing,geodetictransformations,visualisation,andDTMinterpolation.ALSisarelativelynewtechnology,withobviousinfluencesoncosts,systemintegrationandprocessingmethodsmaturity,numberofproviders,etc.

1.2.Majordifferences

ThemajordifferencesbetweenphotogrammetryandALSare:

passivevs.active,high-power,collimatedandmonochromaticsensing;generallyframeorlinearsensorswithperspectivegeometryvs.generallypointsensorswithpolargeometry;fullareacoveragevs.pointwisesampling;indirectvs.directacquisitionorencodingof3Dcoordinates;geometricallyandradiometricallyhighqualityimageswithmultispectralcapabilitiesvs.noimagingormonochromaticimagesofinferiorquality;andabilityforALSto‘see’objectsmuchsmallerthanthefootprint（smallopeningsbelowvegetation,powerlines,etc.）.Allotherdifferencesareaconsequenceoftheabovementionedones.Additionaldifferencesexistwithrespecttotechnologymaturityandpotentialforfurtherdevelopment.Fromaproductpointofview,ALSiscurrentlyavailableonlybyserviceproviders,whilephotogrammetricsystemscanbefoundonprivatedesktopsallovertheworldwhereuserscangeneratetheirowndata.

1.3.Commonaspects

CommonaspectsbetweenphotogrammetryandALSinclude:

（i）useofGPS,andwithdigitalphotogrammetricsensors,especiallylinearones,GPSrINS;（ii）methodsforprocessingofrawdata,likefilteringoflargeerrors,removalofnon-DTMobjectslikebuildings,datareduction（thin-out）andcompression,anddetectionofbreaklines,aresharedbetweenALSandimagematchingforDSM/DTMgeneration;（iii）furthermore,whenlaserdataareregularlyinterpolated,theycanbetreatedasimagesandvariousimageanalysis/processingtechniquescanbeappliedtothem.

Thus,sensorintegrationandimage（ordigitalsignal）processingandanalysisaretwoimportanttopicsthatunifythetwotechnologies.

2.Comparison

Themaincommonapplication,andcompetitionfield,betweenphotogrammetryandALSisthe3Dmeasurementofsurfacesandsingleobjects.ThereasonisthatclassificationandidentificationofobjectswithALS,withoutuseofadditionalopticalsensors,isverydifficulttoimpossible.Beforemakingacomparisonbetweenthetwotechnologies,onemainideawillbelaidout.Measurementwithoutinterpretationissometimesverydifficultorimpossible.Asanexample,tomeasurebuildingsamongmillionsofothermeasurementsonotherobjects,first,themeasurementsonbuildingsmustbedetected（thisinvolvesclassificationofmeasurements）andthenthebuildingsmustbemodelledbasedonthedetectedmeasurementsandotherapplicationdomainknowledge.Sinceinterpretationbasedsolelyonrange/heightdataisdifficult,thismakesclearthatimageswhicharespatially,andformultitemporalanalysisalsotimewise,co-registeredwiththelasermeasurements,areoftenanecessarysupplementforinterpretation,andthusmeasurement.Aninterpretationisoftennecessaryalsoforsurfaces/objectsmoregeneralorspecificthanbuildings,sinceeachcustomerusuallyhasconcreterequirementsonwhathastobemeasured.

2.1.Availablesensors

Thevariabilityofpassiveopticalsensors（POS）isimpressive.Dependingontheapplicationrequirements,therearesensorsofdifferentgeometry（2D,linear,multiplelineones,pointdetectors）,differentformat,geometric,radiometricandspectralresolu-tion（includingnumber,centralwavelengthandwidthofspectralbands）,geometricaccuracy（metric,semi-metric,non-metric）,storagemedium_analogue,digital.,weight,powerconsumption,cost,etc.ALSsystemsoffermuchlessvariabilityandflexibility.Digitalsensorswithpanchromatic,multispectralorhyperspectralpropertiesbasedonlinearorareaCCDsanddetectors（insomehyperspectralsystems）areusedinacontinuouslyincreasingdegree.Typicaldigitalsensorsincludestandardvideo,stillvideo（B/W,colour,IR）,custom-madeonesusinglargeareaCCDs（usuallyonlyB/W）,andlinearCCDs（oneormoreforalongtrackstereo,andspectralsensing）.

ThemaincomparisonofALSwithpassiveopticalsensorsiswithphotogrammetricfilmcameras,theexpecteddigitalphotogrammetriccameras（one3-lineCCDbasedsystemannouncedforsummer2000）,andlesswithlargeformatareaCCDbasedsensors（currently,sensorswith20002–40002pixelsareused）.Photogrammetricfilmcamerasofferalargeformat,atypicalresolutionwithFMCofca.60lp/mm,lensesofvariousfocallengthsandverysmalldistortion,largestoragecapacity（ca.500imagesperrollfilm,correspondingto200GBofdataforB/Wfilmat12mmscanpixelsize）;also,theyareveryrobust,stableandwellcalibrated.Furthermore,condensationandhightemperature,thelatterbeingcausedbytheverylowefficiencyoflasersandthetransformationofthelostpumpedenergyinheat,canimpairlaserperformanceandshouldbecontrolledmuchtighter.PowerrequirementsforALSarealsohigher,whilesomesystemscannotbemountedinstandardaircraftholes.POSsensors,andphotogrammetriccamerasinparticular,provideaneasier,lesscomplexandmo