Data. Visualization process. Segmented, adapted, chosen data. Sampled or simulated (original) data. Display Data (geometry information)

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1 Waltz{AnExploratoryVisualizationtoolforVolumeData, usingmultiformabstractdisplays ComputingLaboratory,UniversityofKent,Canterbury,Kent,England,UK JonathanC.Roberts simplifying(orabstracting)thestructureoftheviewedinformation;andlinkingobjectsandviewstogether(allowing toaidauserinterpretdatacorrectly.theseare:displayingthedataindierentforms(multiformvisualization); Although,visualizationisnowwidelyused,misinterpretationsstilloccur.Therearethreeprimarysolutionsintended ABSTRACT correspondingobjectstobejointlymanipulatedandinterrogated). andrene'visualizationcycle. endofalongvisualizationprocess.ourvisualizationsystem,basedonanadaptedvisualizationmodel,allowsa displaymethodtobeusedthroughoutthevisualizationprocess,inwhichtheuseroperatesa`display(correlate) howeverthatcurrentvisualizationsystemsdonoteectivelyutilisethedisplay,forexample,oftenplacingitatthe Thesewell-knownvisualizationtechniques,provideanemphasistowardsthevisualizationdisplay.Webelieve Keywords:Visualization,Visualizationsystem,Multiform,Manipulation,Abstraction befurtherdisplayed,manipulatedandltered. manipulated;asetof`portionsofinterest'canbeselectedtogenerateaspecializeddataset.thismaysubsequently Thisdisplayintegrationprovidesausefulexplorationenvironment,whereobjectsandviewsmaybedirectly ifthepictureisincorrect:byalgorithmicerrors,accumulatedduringtransformations,orinherentinthealgorithm atacertainresolution?then,theusermaymisinterpretormisunderstandtheunderlyinginformation. Theadage\apictureisworthathousandwords"providesapowerfulincentiveforvisualizingdata.However,what 1.INTRODUCTION scientistwantingtodiscoverfacts,auserinvestigatingandclarifyingthescientistsworkoraresearcherpresenting results,theaimsarethesame:toperceiveandgaininsightoftheunderlyingdatabyinvestigatingrelationships, dependenciesandproportionsintheinformation. Understandingphenomenafromtheunderlyingdataisthemainreasonfordoingvisualization.Whether,itisa information.westate:explorationtechniquesfocusingoninteractionmethodsandthevisualizationdisplayare thevisualrepresentationstheusergainsabetter,andhopefullymoreaccurateunderstandingoftheunderlying usefulfor`correctinformationdissemination'. Scienticinvestigationandexplorationisconsequentlyimportant:as,bymanipulatingandexperimentingwith allowtheusertoquicklydisplayarepresentationofthedata,andthenfurtherrenethevisualization. Ourvisualizationsystemprovidesa`display,rene,display'cycleasaseriesofmini-dataowpipelines,which Inreal-life,anexplorer,wishingtonavigatefromCityAtoTownB,wouldusemapsatdierentscales.First,they representationshowingtheminorroads.thelargescalemapprovidescontextinformationforthedetailedmap. wouldlookatamapshowinganoverviewofthemajorroadconnections;thentheywouldlookatadetailedmap 2.THECONCEPTS understandthedetailedinformation. details.thistwo-levelapproachprovidesstructuredinformationtotheuser,whoisthen,inabetterpositionto Likewise,inscienticexploration,itisbesttounderstandtheinformationasawholeentity,thenlookatspecic allowcomplexanddiverseoperations,butdonotprovidetoolsthatencouragetheusertousethisconcept.moreover, Fromthisexample,weproposethatvisualizationsystemsneedtoadoptthistwo-levelpolicy,currentsystemsdo Otherauthorinformation:

2 Filter Map Display Data Segmented, adapted, chosen data Display Data (geometry information) Sampled or simulated (original) data Visualization process Figure1.Thetraditionalvisualizationprocess:Filter,Map,Display toachievethisstyleofexplorationonscienticdata,asklinkermentioned,1imagingtoolsneedtoprovideinteractive mechanisms,allowingtheusertointerrogateandunderstandrelationshipsanddependencieswithintheinformation. Webelievethattherearethreeprimary(andpowerful)visualizationtechniquesthataidtheusertoexplore andgenerateacorrectinterpretationoftheunderlyinginformation.first,displaythedataindierentforms{ Multiformvisualization.Second,displaytheinformationinsimpliedAbstractviews.Third,provideahighdegree ofinteractionanddirectmanipulation. Multiformvisualizationistheprocessofdisplayingthesameinformationinmultipleways.2Thisenablestheuser tounderstandtheinformationfromdierentperspectives,helpingtoovercomeconfusionandmisinterpretation frombelievingtheresultfromasingularvisualizationmethod.thishasbeensuccessfullyusedtodisplay multivariatedata,asexempliedbythexmdvtool,3andwe,likeyageletal,4advocatetechniquesthat utilisedierentrenderingschemestouncoverdierentaspectsinthedata. Abstractviewsrepresentsimplied,augmentedorstructuralrealizationsoftheinformation.5Thistechnique generatesmultiformviews,asabove.however,theseviewsaregeneratedbythesamealgorithmwithdierent simplicationcriteria.forexample,asurfacealgorithmmaybegeneratedatahighresolutionwithmany surface-trianglesoralowresolutionwithfewertriangle-elements,thelatterwouldberenderedfasterand providesasimpliedversionoftheinformation.thissimplicationisusefulfor`fastinteractive'navigation, asusedbythevolvissystem,6forexample. Infacttheabstractionmayoccurateitherthedataortheimagelevel.Atthedatalevel,theinformationcontent maybereduced(simplied)bysamplingorgroupinglikeobjectstogether;forexample,silver7segmentsthe dataintogroupsnamedobjects,thatmaybetrackedastheyevolveandmovethroughoutthedata.8at theimagelevel,thevariableorattributesbeingmappedontothedisplaymaybealtered.forexample,the trianglesmakinguptheisosurfacemaybeexchangedtolinesorpoints;thiswouldallowotherwiseoccluded objectstobeseen.alternatively,thepositionoftheobjectsmaybeaugmentedtofacilitatetheunderstanding ofthedata.forexample,sheelaghetal9usethistechniquetoprovidea`clearlineofsight'toobscuredan concealedsectionsofthedata. Theabstractviewsmayallowobjectsthatarenormallyoccludedtobeseen,orgenerateastructuralviewof thewholedata.theyprovidetheuserwithadditionalinformationaboutthestructureofthedata:usefulfor a`correctdissemination'oftheinformation. DirectManipulationallowsobjectswithinthedisplaytobedirectlyinterrogated,scaledandpositioned.This interrogationisalsopropagatedtorelatedviewsofthesamedata,toprovidejointinteractivedataprobing andobjectmanipulation.thisissimilartothebrushingtechniqueofward,3thatallowselementsinoneview tobebrushedbythemouse,coincidentallyhighlightingcorrespondingelementsinrelatedviews;andsimilar tothemanipulationlinkingtechniqueusedintelecollaboration1orbyothersystems.10{12 3.THEWALTZEXPLORATIONMETHOD TheMultiform,AbstractandManipulationmethodsarewell-knownvisualizationtechniquesandtheiremphasisis towardsthedisplayedimage.userswishingtoexplorethevisualizationneedtoconcentrateonthevisualoutput andnotthevisualizationprocess.however,webelievethatcurrentvisualizationsystemsdonoteectivelyintegrate

3 Traditional connected dataflow pipeline A Data Filter Map Display Filter Map Display Dataflow connected using the display filter method B Data Filter Map Display Filter Map Display thedisplayintothevisualizationprocess,oftenplacingitattheendofalongsequenceofcommands.thislong visualizationprocessisverypowerful,comprehensiveandextensible,andisoftendescribedbythedataowmodel. Figure2.Thedisplayactingasalter,thatmaybefurtherdisplayedandltered data display filter an additional filter specialization operation included visualizationsystemsarebasedonthismodel.14{18 displayed,figure1.thisworkisoftenaccreditedtohaberandmcnabb13andupsonetal14andmanyexisting Where,thedataisltered,tocreateasubsetofthedata,whichisthenmappedintoarepresentationwhichcanbe Thedataowmodeldescribesthevisualizationprocessasaseriesofthreeprocesses:lter,mapanddisplay. thevisualizationtasks,byprovidinganintelligentuserinterface.forexample,woodetal19mentionthethesisof Stead,andtheVISTAsystem20providesaseriesofrulesthatappropriatelydisplaythevisualization.Suchsystems pretation.onesolutionistoshortenthevisualizationcycle.thismaybeachievedbyautomatingsomeorallof donotemphasiseexplorationtechniques.analternativemethodmayconsequentlybegeneratedbyintegratingthe Webelievethislengthyvisualizationcyclemaycausefrustrationandconfusion,leadingtoinformationmisinter- thenbefurtherlteredanddisplayed. displayintothevisualizationpipeline,byallowingthedisplaytoactastheinformationlter.theltereddatamay informationhasbeenspecialized.thisnewdatasetmaybefurtherlteredanddisplayed.thediagram,figure2b, operation,figure2b.thus,thedatahasbeenrenedthroughthisdisplay-lter,andanewdatasetisformedby makingasubsetfromaselectionoftheinitialdataelements.wenamethisnewdatasetadataspecialization,asthe alsoshowsthattheorderoftheprocesseshasbeenalteredtomap,displayandlter.thisallowssomelterprocess Thislteroperation,namedadisplaylter,21allowstheoutputfromonedisplaytobeinputtoanotherlter tobeomitted,enablingtheselectedobjectstobedisplayedwithoutbeingrened.moreover,thespecializeddata maybeadditionallylteredbythereceivingmini-pipeline.obviously,multipledisplay-lteroperationswillgenerate aseriesofchilddata-specializations,whichmayformadata-hierarchyofsubdatasets,figure3. Filter Map Display Filter Map Display Figure3.Ahierarchyofdataselectionsmaybegenerated Filter Map Display Filter Map Display Filter Map Display

4 Thedatawithinanyofthedata-specializationsmaybedisplayedinmultipleforms,consequentlygeneratinga groupofrenderers.4anothervisualizationmethodmaybeaddedtothisdisplay-groupbysimplyrequestingthe appropriatemethod. Themanipulationofelementsisalsoscopedbytherender-group.Thisallowsthesameobjects,butindierent views,tobejointlymanipulated.forexample,objectswithinasurfaceandaskeleton-displayofthesameinformation maybejointlymanipulated:scaled,rotatedortranslated.ourmanipulationoperationsjointlytransformtheviewing projection(inthreedimensions)orhighlightandtransformindividualelements.additionally,wegrouptogetherthe mapping-attributes,sothehue,colourortransparency(ofthemappedobjects)maybecoincidentlyaltered. Thisstyleoflinked-manipulationissimilarlyimplementedinsystems,suchas,Klinker1inAVS,KBVision,10 LinkWinds11andSciAn,12but,ratherthanallowtheusertojoinappropriatelinks,ourdisplay-groupmethod allowsthelinkingtobeautomaticallyprovidedbythesystem.thelinksareautomaticallyaddedtotherelevant displayswhenanewdisplayisaddedtothelist,thussimplifyingtheuserinteraction. Theuserinterfaceisfurthersimpliedbycoercingtheprocessesofthemini-visualization-pipelineintoonemodule. Thisonemoduleallows,throughmenuselections,thelter,mappinganddisplayoperationstobeperformed.Thus, tocreateanewmoduletheuserselectstheexportmenu,thatautomaticallygeneratesanothermodule.thistechnique couldbedescribedasbeingamixtureofamodulebuildingenvironmentandamenu-basedvisualizationsystem; becauseoftheuser-controllablenetwork,withmenu-basedcommands. Further,wehavedevelopedamodule-manager,thatautomaticallypositionsthemodulesontheworkarea,taking theresponsibilityfromtheuser.anewwindowisgeneratedforeachdisplay,sothemanagerlabelseachwindow withauniquereferencenumber,relatingtheseparatewindowstothework-area.themultiformdisplayspersist throughoutavisualizationsession,enablingthedisplaystoprovidea`history'ofpreviousexperimentations. Oursystemincorporatesthedisplayasarst-class-citizen,byincludingthedisplayoperationasanintegralpart ofthevisualizationprocess.thisencouragesandsupportstheuserto,rst,displaythesamedata,andaspectsof thedata,usingdierentrenderingschemes.second,providedirectmanipulationoftheviewsandobjectswithin resultantvisualizations,toallowtheusertodirectlyselectobjectswithinthedatatoenablethedatatobeltered. Third,toautomaticallylinkcorrespondingfeaturesbetweenvisualizations,allowingobjectsandviewstobejointly manipulated.thevisualizationprocessthenbecomes:aprocessof`display(correlate)andrene'operations. 4.EXAMPLES{AUSER'SVIEW TheWaltzsystemhasbeendevelopedforvolumedata.Webelievethemethodologycouldbeeasilyextendedto otherdata-types,alongwiththehigh-leveluser-interfaceimplementation.however,thelow-leveldatastructure wouldneedtobegeneralizedtosupportotherdatatypes. Todescribetheoperationandcontrolofthesystem,wewillworkthroughtwoexamplesessions.Therstexample usesatestdatasetcontainingconcentricthree-dimensionallayers. Onstartup,acleancanvasispresentedtotheuser.Arstmoduleisautomaticallyplacedonthecanvaswhen thedataisloaded.thisrstmoduledisplaysthele-name,holdstheimporteddataandactsastherootnodeon theworkarea.subsequent`children'modulesarealwaysofthedisplay-grouptype.thelteroperationontherst display-groupmoduleisusedtoprocessthedataelementsintoobjects.currently,onlyonealgorithmisprovided, thatclustersthe(individual)dataelementsintosetsofsimilarvalue.thealgorithmusesaoodingtechniqueto thresholdandconnectthedata.initially,noimagesaredisplayed,butadditionalrealizationsareadded(anddeleted) byselectingtheappropriatedisplay-groupmenu.initiallyweaddasurfacerendering;however,asthewholedataset isanobjectitself,athree-dimensionalcubeisrendered,andtheinternalstructureremainsunseen.therefore,we addaslice-display,enablingtheinternalstructuretobeviewed,figure4. Throughourexplorationwerealizethattherearemultiplepartstothedataset;wecaneitherre-evaluatethedatasegmentationinthismoduleoraddanothermodule:asachildofthedata-lemodule.Infact,whenthesegmentation isre-evaluated,eachdisplaymethod(withinadisplay-group)automaticallydisplaysthenewinformation. Weaddanothermodule,Figure5,thistimeweprocessthedataintotwogroups:theinteresting-featureand thesurroundingair.thefeatureisselected,consequentlyhighlightedbythesystem,andafurtherdisplay-module isgeneratedholdingonlythisfeature,towhichweaddasurface-displayandalist-display,figure6.thelistmoduledisplaysthreegroups:theobjectandtwopaddinggroups(alltheelementsoutsidethisandtheprevious specialization).

5 displaywindow) Figure4.TheWaltzworkarea,showingthedata-lemodule,agrouped-displaymodule(withasliceandsurface- Figure5.Twonewgrouped-displaymodules,evaluatedintotwointeresting-feature,shownbytheslice-display intoafourthgroup-displaymodule,andasurface-displayisaddedtothismodule.bymethodssimilartothisthe aslice-display,figure7.thensomeoftheelements,specically3,4,5,6,7asseenfromthelist-display,areexported usercanexploreandfocusonspecicpartsoftheinformation. Finally,were-evaluatethegrouped-featuresonthisthird-moduleandincludeabounding-boxabstractionand wishtobothdisplaythemainsurfaceandinvestigatethepressureswithinthedata. isbombardedwithasmallerpieceofmaterial.thedatasetdescribesthepressureintheblock.fromthisdata,we Initially,wedividethedatasetintotwointerestingfeatures:theblockandair,Figure8.Boththesliceand Thesecondsessionvisualizesthedatafromaspacedustimpactsimulation;whereastationaryblockofmaterial grouped-displaymodule.thissecondmoduleisusedtodisplaytheblocksurface. surface-displayareusedtorealizethefeatures.theblockisthenselectedandexportedtogeneratedthenext objectspecializationinthethirdmoduletogeneratemultipleobjects.towhich,weaddsurface,bounding-boxand network-displays,seefigure9. Insimilaroperationtogeneratingthesecondmodule,wecreateathirdmodule.Were-segmentthesingle- Userinterrogationmaybeperformedonthedata.Forexample,theobjectsmayberotated,Figure10or

6 Figure6.TheWaltzworkarea,showingthedata-lemodule,agrouped-displaymodule(withtwoabstractions: theslice-displayandasurface-display) transformedfigure11.theinteractionisautomaticallydirectedtotherelevantobjectsofeachrendererina Bounding-box,Surface,listandslicedisplays. Figure7.Thedatainthethirdmoduleisrenedfromtheone-groupintosixgroups,andrealizedusingthe particulardisplay-group. ThenameWaltziscoinedfromthemusictermofthreepartsinfour,fromtheMultiform,AbstractandManipulation processeswithinagraphicaluser-interface. WaltzhasbeendesignedinC++withclassesrepresentingthedata,groupingsofthedataandabstractions, 5.IMPLEMENTATION andisimplementedoverxandxlibusingthemotifwidgetset,inventor22andopengl23libraries.foradetailed descriptionoftheimplementation,see.5

7 exported.thesecondmoduledisplaysthesurfaceoftheblock. Figure8.Therstmoduleisusedtosegmentthedataintotwofeatures;theimpact-blockisthenselectedand Sowhenanewmoduleiscreatedthemanagerpositionsthewidgetsinthedesiredposition.Likewise,asnew Themodule-managercontrolsthepositionsofthemodulesandiscontrolledusingtheXcallbackmechanism. Figure9.TheWaltzworkareashowingonedata-lemodulewiththreegroup-displaymodules. display-abstractionsareaddedtothedisplay-groupthemodule-manageriscalledtoupdateworkarea. hascontrol-structuresallowingupanddowntree-traversal. ulators.threedimensionalmanipulators(jacks)areappliedtotheobjectsintheinventorscene-graph.togenerate ThemanipulationwithinthedisplaysiscontrolledusingboththeXcallbackmechanismandtheInventormanip- Themodule-managerstoresthemodulehierarchyinformationinatreedata-structure.Forconveniencethetree thelinkedmanipulationwithinthegrouped-displaymodule,thecodereferencesoneinventor-manipulator,thatis placedineachdisplay-method'sscenegraph.infact,individualmanipulatorscanbeswitchedintothegraph,to allowspecicmanipulation.thisswitchiscontrolledbyaradio-buttonselectiononamotif-basedform. to24),withalistofthegroupsandtheiradjacencyinformation. data.relevantpartsofthedataarecopiedandexportedfromonemoduletothenext.thisexportoperationis controlledexplicitlybythesystemuser.eachdatashadowholdsthegroupingsdataasanarrayofslices(similar ThedataisstoredinaDataShadowclass,thatholdsinformationaboutthegroupingsandspecializationsofthe

8 Figure10.Thewholeviewmaybedirectlymanipulated.Thecontrolislinkedbetweenviewswithin thesamedisplay-group.theimagesshowthreeviewsbeingrotated. Figure11.Individualdataelementsmaybedirectlytransformed.Thecontrolislinkedbetween viewswithinthesamedisplay-group.theimagesdepictonegroupbeingtranslated.

9 Wehavepresentedasystemthatprovidesexplorationtechniques,especiallyforthe`correctdissemination'ofinformation.Weacknowledgethatexplorationisonlyonemethodtosuppressmisinterpretation.Butwebelieveittobe 6.DISCUSSIONANDFUTURERESEARCH animportantone!furtherworkisrequiredinthis`correctdissemination'area. ItistruethattheModulevisualizationenvironments(AVS,IRISExploreretc,25)allowmultipleviews,butinour experiencethesetendtobeexpensive:usingtime,processingandmemoryresources.thus,therearesomeadvantages inhavingmultiplelightweightrenderingwindows,suchasprovidedbywaltz. Oursystemprovidesmethodsthatencouragestheusertoperformmultipledisplaysofthesameinformation. ofpreviousexperimentations.infactwebelievethatabstracttechniquesareuseful,becausetheyprovidesimpler anddiverseinterpretationsoftheunderlyinginformation.althoughsomeabstracttechniquesaremeaninglessin occludedelements,forexample,tobeselectedandmanipulateddirectly. isolation(suchasthelist-display)theycanactascontrol-abstractions,andwhenlinkedwithotherviewstheyallow Themultiformdisplayspersistthroughoutavisualizationsession,enablingthedisplaystoprovidea`history' features,andtomanagethecontrolofthelinked-interactionandtheplacementofthemodules.othersystems,such asthetelecollaborativeenvironmentdescribedbyklinker1orthevisualizationinputpipeline26provideextensible webelievethatitisusefultoallowtheusertolterthedatathroughthedisplay,bysegmentingtheinformationinto interactivevisualizationsystemsbutdonotmanageeitherthelinked-interactionorthemodule-layout. OthersystemssuchasSciAn12andLinkWinds11providemultipleviewsofthedatainalinkedenvironment,but, neatlayout!problemswiththislayoutwouldoccurinalongsession.currently,modulesmaybedeletedandthe together,andreducestheirsize,toallowlargernetworkstobevisualizedonthework-area. workareascrolled.butitwouldbebenecialtoapplyamorecomplicatedalgorithm,that(say)groupsthemodules byreducingtheneedforadditionalpipesorlinksandstopstheuserfrom`wastingtime'movingthemodulesintoa Webelievethat,bymanagingthemodule-layout,theuserreceivesadditionalinformation,simpliesthenetwork example,thevistasystem20,27operatesbygeneratinganappropriaterealizationfromalistofordered,anduser preferencedvariables.thistechnique,maybeusefulfornaiveandinfrequentusersbutexpertusersmaywishfor morecontroloverthegeneratedvisualization.indeed,misinterpretationsgeneratedthroughthewrong-useofthe visualizationprocesswouldbesignicantlyreducedusinganintelligentsystemapproach. Theintelligentvisualizationsystemstakethesystemandinformation-managementtechniquetotheextreme.For ltertechnique.thedisplay-ltermethodprovidesanintuitivelteringmethod,albeithardertoimplementand technique,withsixdisplaymethods.othertechniqueshavebeenproposed,butareleftforfuturework.moreover, lessdiversethantraditionaltechniques.infact,thecurrentimplementationonlyprovidesonedata-segmentation theabstractiontechniquecouldbeappliedmorevigorouslytothecurrent(andfuture)displaymethods.thecode, However,anintelligentapproachdoesnotallowsomuchuser-exploration;suchasprovidedthroughadisplaytechniqueanewsub-classisrequired,andthesystemre-compiled. wasdesignedtobeextensibleespeciallytheuserinterface,butinpractice,foreachnewsegmentationordisplay informationinterpretation. displayedrealizations.comparativevisualizationtechniques28mayprovideadditionalinformation,aidingacorrect Themultiformlinkeddisplaysprovideausefulexplorationenvironment,however,theusermanuallycomparesthe fromitsoriginalpositionandautomaticallyreplaceditwhentheuserreleasedcontrol. intocompoundoperations,forexample,anoperationmaybedesignedto`lookandsee',thatmovedafeatureaway niquescouldbeimplemented.currentresearchistakingplaceinthisarea.someofthemechanismscouldbemade Waltzcurrentlyimplementsselectionandtransformationstylesoflinking.Furtherbrushing3andlinking1tech- WehavepresentedavisualizationsystemincorporatingMultiform,AbstractandManipulationtechniques,forthe correctdisseminationofscienticinformation.wehaveadvocatedtheuseofexplorationtechniques,andacknowledge thatexplorationisonlyonemethodtosuppressthismisinterpretation. 7.CONCLUSION visualizationandcorrectdisseminationinauserextensibleframework. WeproposetodevelopandextendtheWaltzsystem,toincorporateandprovidemechanismsforexploratory

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