Real time 3D display of hydrographic data for QA a

Realtime3DdisplayofhydrographicdataforQAandQC.RolandArsenaultCenterforCoastalandOceanMapping&[e-mail]dingsystem(RTG)isbeingdevelopedtoenablerealtimequalitycontrolduringmultibeamsonarsurveys.RTGdisplaysgeoreferenced,griddeddataasitiscollectedfromthemulti-beamsonar.Thesystemiscapableofintegratinghistoricdata,suchascharts,DTM'sandsidescansonarimages,whilebuildingasurfacethatgrowsasthenewdataisbeingcollected,allinageoreferenced3Denvironment.Otherdata,suchaspositionandattitudeoftheshiportowedvehiclecanalsobedisplayedinrealtimeinordertogivetheuserafullpictureofthecompletedataacquisitionprocessasitishappening.Therealtimedisplayofgeo-referencedsoundingdataisaninvaluabletoolforidentifyingbothsystematicartifactsandoutliers.ThetechnologythatFigure1–DatacollectedfromaSimradEM1002intheGulfofMexico.Themainwindowshowsanoverviewofrecentdatacollected,whilethesubwindowshowsaclose-upviewofadiagramrepresentingtheshipanditsattitude.enablesRTGconsistsofadynamicallygrowingsurfacethatisgriddedon-the-flyandrealtimedisplayusingvariableresolutiontomaintaininteractivitywiththesystem.Anumberofdisplaymodeshavebeenimplemented,includingdisplayingofallsoundings,displayingthemediansurfaceorshoal-biasedsurface.BoththederivedDTMandtheunderlyingsoundingscanbedisplayedsimultaneouslyrevealingtherelationshipbetweenthesoundingsandtheDTM.IntroductionInacomplexsystemsuchasamultibeamsonarsurveysystem,itisverydifficulttoeliminateallsourcesoferrors.Someoftheseerrorscanbecorrectedifdiscoveredearlyenough.Itisthereforecrucialtopinpointandcorrectasmanyerrorsaspossible,asearlyaspossibletoincreasedataquality,andreducetheamountoferrorcorrectionnecessaryinpostprocessing.Thisproblemcametomyattentiononmyfirstmultibeamsurveycruise,amultibeamsurveyofthePinnaclesareaintheGulfofMexico[Gardneretal].Duringthatsurvey,valuabletimewasspentdebuggingtheinstallationofthesurveyequipment.Timewasalsospentreprocessingdatatocorrecterrorsdiscoveredlaterinthesurvey.Withmylimitedknowledgeofmultibeamsurveysystems,Idevelopedaprototypesystemtovisualizethegeo-referenceddataasitwascollected,alongwiththepositionandattitudeofship,soIcouldbetterunderstandtheproblemsencountered.Itquicklybecameobviousthatsuchasystemcouldbeveryusefultomultibeamsurveyoperators.OnamorerecentsurveyofPortsmouthharbor,inNewHampshirebyNOAA,itwasobservedthatdeterminingifthepropercoveragewasachievedsometimestookasmuch24hoursasdatafromtheday'ssurveywasprocessedatnight.Immediatefeedbackofareaeffectivelycoveredwasnotavailable.Itwaspossibletoknowwhichareasforwhichsoundingswereavailable,butwithoutpostprocessing,thequalityofthedatawasnotknown,andtheeffectivecoveragecouldnotbeeasilydetermined.Tohelpinidentifyingpossibleerrors,andhelpincoverageassessment,arealtimegriddingsystemisbeingdeveloped.Therealtimegridallowsasurfacetogrowassoundingsareadded.Thesystemisalsocapableofdisplayingtheship'spositionandattitude.Thisisusefulinfindingconfigurationerrors,suchasincorrectpitchorrollcorrection,bymatchingattitudewithartifactsinthesoundingsandresultingsurface.Thesystemcanhelpincoverageassessmentnotonlybydeterminingwhatareasarecoveredbypings,butbyimmediatelydisplayingasurface,lowqualitypingsmightbebetteridentified,andareasofinterestcanalsobeidentifiedandextrapassescanbeaccomplishedrightaway,ifsodesired.Variousmethodsofintegratingnewsoundingsinthesurfacemaybeused.Thesystemcanusesimpleaveragingormedianfilters,orcouldincorporatemoresophisticatedalgorithmstoproduceasurface.Thefollowingsectionswilldescribethetechnologydevelopedtoenablesuchasystem.TechnologyToday'smultibeamsonarcollectsmoredatathatcanbedisplayina3dinteractivemanner.Onemethodofshowingapictureofdensehydrographicdataistobinthesoundings,thenusingstatisticaltechniquesselectasinglevaluetorepresentthatbin.Withthiscollectionofrepresentativevalues,laidoutinaregulargrid,itispossibletodisplayinteractive3dsurfacesoftheareacoveredbythosesoundings.Thefollowingmethodwasdevelopedtoallowthedatatobeassignedtobins,andsurfacestobecreatedinaninteractivemannerwhilethedataisbeingcollected.RequirementsThecollectionofdataandrealtimedisplayofasurfaceintroducesmanyrequirementsonadatastructuretoholdthisdata.Thedatastructuremustallowefficientaccesstoarandombininwhichtodeposittheincominggeo-referenceddata.Thedatastructuremustalsoalloworderlyaccesstothebinvaluestoconstructthedisplayedsurface.Itisalsoimportant,toachieveacceptablerenderingspeed,tokeepthebinvaluesinmemory,ratherthanswaptodisk.Anotherusefulfeatureistohaveastructurethatcangrowwithoutpriorknowledgeoftheboundsoftheincomingdata.Thiseliminatestheneedtoestablishboundsbeforedataiscollected,andallowstheflexibilitytocollectdatainareasthatmightnothavepreviouslybeendefinedtobewithintheboundsofthecurrentsurvey.DesignAdatastructurehasbeendesignedwiththoserequirementsinmind.Thestructureisbasedonaquadtree,withalinkedlistconnectingitsnodeintorowsandcolumns.Aquadtreeisastructurewithtwoindices,onerepresentingthexvalueofanx,ypair,andthesecondrepresentingtheyvalue.Thetoplevelofaquadtr