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1 AnArchitectureforMotionCaptureBasedAnimation FernandoWagnerSerpaVieiradaSilva1;2 LuizVelho1 PauloRomaCavalcanti2 JonasdeMirandaGomes1 1IMPA{InstitutodeMatematicaPuraeAplicada EstradaDonaCastorina,110, 22460RiodeJaneiro,RJ,Brazil 2LCG-LaboratoriodeComputac~aoGraca,COPPE-Sistemas/UFRJ ,RiodeJaneiro,RJ,Brazil,CaixaPostal68511 Abstract. Thispaperproposesanarchitectureformotioncapturebasedanimationsystems, thatworkswithseveraldataformatsandusesthebuildingblockparadigmformotionprocessing operations.also,auserinterfaceisproposedtoperformanintuitivevisualizationoftheanimation mainelements.aprototypesystemhasbeenimplemented,basedonthepresentedconcepts,and itsoperationisdiscussed. keywords:motioncapture,computeranimation,motioncontrol,animationsystems,gui paradigm. 1Introduction Recently,thecrescentdemandforpowerfulandintuitiveanimationsystemshasledtothedevelopment ofnewtechniques,givingtheanimatormoreversatilitytobuildcomplexanimations. TheMotionCapturetechniqueprovidestools forreal-timeanimation,withmorerealisticresults thantraditionalanimationtechniques.thewidespreaduseofmotioncapturetechniquesisinpart duetothelowcostofmoderncapturingsystemsand alsotothedemandofdierentapplicationareassuch asspecialeectsandhomeentertainment. Althoughithasbeenstudiedsincethebeginning ofthe80's[1][2],thepresentutilizationofmotion captureisrestrictedtoadirectmappingofanimation parameters.inotherwords,themovementscaptured fromlivesubjectsaremappeddirectlyonavirtual actor,andthentheanimationisdisplayed.inspite ofitsvalue,thisuseisverylimitedanddonotexploit allthepotentialofthemotioncaptureprocess. Lately,however,toolsforanalysis,manipulation andreuseofcaptureddatahavebeenproposed.this makesmotionlibrariesmorevaluableforawideclass ofanimators. Theapplicationofthesetechniquesareunlimited,fromthedevelopmentofcomputergames[4] totheproductionofcomputer-generatedchoreographies. Inthiswork1,weproposeanarchitecturefor motioncapturebasedanimationsystems.ourgoal istoembodyasetoftoolsforanalysis,manipulation andreuseofmotioncaptureddata,overcomingsome limitationsinherenttotheprocess. Thearchitecturewasdesignedtoserveasatest bedfornewtechniques,andalsoworkasarobust converterbetweenthemostpopularmotioncapture dataformats. Section2ofthispaperdiscussessometechnologicalaspectsofmotioncapturesystems,pointing outsomelimitationsoftheprocess.insection3, wepresentamethodfor3deulerangleextraction, thatisusedtogeneraterelativeangles.section4 discussesaclassicationformotionoperations.in section5,wepresentthearchitecture,togetherwith thedescriptionofauserinterfaceforthesystem. Section6presentsaprototypeimplementation,developedunderthemethodologyofourarchitecture. Finally,conclusionsandfutureworkaregiveninsection7. 2Background Thereisalargediversityofmotioncapturehardware availablenowadays,fromsimplemechanicdevicesto sophisticatedopticalsystems. 1Additionalinfoavailableat 1

2 AnArchitectureforMotionCaptureBasedAnimation 2 Mechanicalsystems[5]arecomposedofpotentiometers(orsliders)thatmeasurethepositionor orientationofjointsinanobject.itssimilaritywith conventionalstop-motiontechniques,thatarewidely usedinmovieproduction,allowsanaturalmigration oftraditionalanimators,thusincreasingthepopularityofthistechnique.however,therealismofmechanicallycapturedmotionsstilldepends,ingreat part,ontheabilityandpatienceoftheanimator. Systemsbasedonmagnetictechnologyareprobablythemostpopularones.Bothpositionalandangulardataofthejointsofarealsubjectarecaptured, usingasetofsensorsthatmeasurethemagneticeld generatedbyasource.theirmainadvantageisthe possibilityofreal-timeanimationofvirtualcharacters,thusoeringtothetvindustrynewpossibilitiesintheeldofvirtualsets[6]. Somedrawbacksofthistechnologyarethesensitivitytometalsinthecapturingarea-whichintroducessomenoiseintothenaldata;thehighlevel ofencumbrance-duetothegreatnumberofcables attachedtotheactor;andthesamplingrate-too lowforfastsportmotions. Opticalsystemsarebasedonhighcontrastvideo imagingofretro-reectivemarkers,thatareplaced onobjectswhosemotionisbeingrecorded.this techniqueprovideshighsamplingrates,buttherecordedmotiondatamustbepost-processedusing computervisiontrackingtechniques[7]. Inthetrackingprocess,thecentroidsofmarkersarematchedinimagesfrompairsofcameras,usingatriangulationtocomputethepositionaldataof thesemarkersin3dspace.thisprocessintroduces artifacts(osets)intothenaldata.somedisadvantagesoftheopticalprocessaretheocclusionofoneor moremarkersduringthecapturingsession,thelack ofangulardata,andthesensitivitytobackground lightandreectiveobjects. Hybridsystems[8],thatcombinebothmagnetic andopticaltechnologiesarebeingdeveloped,but arenotyetcommerciallyavailable.aninteresting comparisonbetweenmotioncapturesystemscanbe foundin[9]and[10]. Finally,aproblemthatarisesfromthegreatdiversityofmotioncapturehardwareandtechnologies isthegreatnumberofmotiondataformats,which reducessignicantlythecompatibilityofanimation systems. 3AMethodfor3DEulerAngleExtraction Asdiscussedbefore,oneofthemaindisadvantages ofopticalsystemsisthattheycaptureonlypositionaldataofjoints.angulardataisextremelyimportantbecauseitcanbemappedontoa\positionindependent"skeletonhierarchy,givingmorefreedomtotheanimator. Inananimationsystemwithmotioncapturefacilities,eachjointmayhavebasicallytwotypesof angulardata:absoluteanglesandrelativeangles. Thersttypeisusefultoexecuteadirectvisualizationofthecapturedmotion,butpositionaldatais stillnecessaryforplacingthejointsinspace,ateach frameoftheanimation. Relativeanglesareusefultocreatecomplexanimations,allowinganeasiermodicationofmotion parameters.thepositionalinformationoftherst frameisusedtoplacethejointsinthecorrectpositioninspace(andalsotoestimatethelengthof thelimbs),andthentheanimationisdrivenonly bythejointangles.forexample,arotationappliedtotheshoulderjointwillpropagatetoalljoints ofitssub-tree,i.e.,theelbowandthewrist.the entireskeletonstructurecanbemovedinspaceusingthepositionalinformationofthehips,forexample.besides,techniqueslikekeyframingandinverse kinematicscanalsobeincorporatedasnewfeatures, sincetheycanbeadaptedtoworkinamotioncaptureenvironment. Tocalculatetheseangles,wedevelopedanalgorithmbasedongeometry.Traversingthetopological structureoftheskeleton,ouralgorithmcalculates bothabsoluteandrelativeangles,foreachjointof thestructure. Absoluteanglesareobtainedbyprojectingthe linksoverthecoordinateplaneslyingontheproximal2joint.foreachplane,theprojectedvectoris thennormalizedanditsanglewithrespecttothe currentaxisiscalculated(seegure1). Figure1:absoluteanglecalculation Relativeanglesarealsoretrievedbyprojectingthelinkedstructureoverthecoordinateplanes (gure2).foreachlinkwecalculateaunitvector 2Thetermsproximalanddistalwillbeusedtodescribe positionsas\near"and\distant"fromthepointoforigin.

3 3 F.W.S.V.daSilva,L.Velho,P.R.Cavalcanti,J.deM.Gomes formedbytheproximalanddistaljoints.toavoid ambiguity,weestablishedthatlinksarerelatedin aclockwisemanner.usingthisrule,theprojected linkedstructureingure3willhavetheappropriate angles,asshowningure4. Figure2:linkedbranchprojectionoverthecoordinateplanes Figure3:ruletoavoidambiguityinrelativeangle calculation Usingthepreviouslycalculatedvectorsofthe links,groupedinpairs,wecancalculatetheangle betweenthemusing=cos 1(! AiAi 1N! AiAi+1N) (seegure4). A i-1 A i A i+1 alpha Figure4:groupedvectorsdispositionandangleextraction However,insomecases,thedesiredangleisnot,but=360 (ingure3,anglenumber3). Thiscaseisexpectedandoccurswhenthelinkangle isgreaterthan180.tosolvethisproblem,weusea simpleandfastcriteriatoknowwhetherapointison theleftsideofanorientedsegmentornot.ifapoint cisontheleftofthesegmentdeterminedby(a;b), thetriple(a;b;c)formsacounterclockwisecircuit (gure5).thenanareabasedalgorithm[11]returns thesignedareadeterminedbya;bandc,i.e.,positive ifcounterclockwise,andnegativeifclockwise. a b c Figure5:pointcisontheleftofthesegmentabif (a;b;c)formsacounterclockwisecircuit Usingthis\leftness"criteriaweareabletocalculatethecorrectanglesofthelinkedstructure:if thetriple(ai 1;Ai;Ai+1)hasanegativearea,then wetake=360,andtheprocesscontinues, foreachtripleuntilreachingtheend-eector3ofthe linkedbranch. Finally,thedimensionsofactor'slimbsarealso estimated,measuringthe3ddistancebetweenthe proximalanddistaljointsofeachlink. Thisprocedureisusedasapre-processformotioncaptureddatafromopticalsystems. 4AClassicationforMotionOperations Wecanmakeananalogybetweenoursystemand acsgmodelingsystem,wherebasicprimitives(in ourcase,themotions)arecombinedthroughoperationslikeunion,intersectionanddierence.inour paradigm,however,the(motion)operationsareltering,blendingandconcatenation.theycanbe classiedinthreetypes:unary,binaryandn-ary. Unaryoperationshaveonemotionasoperand, andareusefultomodifyspecialparametersof themotion(e.g.,alteringoperationoverselected joints)oreventomodifytheentiremotion(e.g., warpingthemotioncurves[17]). 3Thetermend-eectorisoftenusedinrobotics,referring tothelastjointofanarticulatedchain.

4 AnArchitectureforMotionCaptureBasedAnimation 4 Binaryoperationshavetwooperands,andits mainpurposeistojoinorgroupdierentmotions, creatingalongerone.examplesofbinaryoperations areconcatenation,cyclication[18]andtransition. Notethatalthoughconcatenationmaybeappliedto severalmotionsinsequence,itcanbecarriedout locallyasanoperationbetweentwomotions. Binaryoperationshavemanyinterestingapplications,fromcomputerghtgamestovirtualreality cooperativeenvironments[19]. Thelasttypeofmotionoperations,n-ary,deals withtwoormoreoperands.motionscanbetotallyorpartiallyblended,generatingnewinteresting typesofmovements.inthecaseofpartialblending oftwomotions,onecanchoosetoapplyawalkmotiontothelegsandhipsofaskeleton,whileletting thetorsoandarmsexecuteadancemotion. Wecanalsogrouptheexistingmotionoperationsinthreetypes,accordingtothemethodofmodicationand/orcombinationtheyperformintheir operands.theyare: Filtering Filteringoperationscanbeappliedtothejoint curvesofamotiontoreducenoise,producing smootherresults. In[12],Williamsuseamultiresolutionlteringmethodtodecomposethemotionintofrequency bands.heshowedthathigh-frequenciescontainthe detailsofthemotion,whereaslow-frequenciescontaingeneral,grossmotionpatterns.inapractical exampleawalkmotionwasprocessed,extractinga basic\walking"factoranda\qualitative"factor,like briskitseemsthatmostdigitallteringtechniques aresuitabletousewithcapturedmotiondata. Concatenation Concatenationoperationscanbeusedtocreatelongeranimations.Smoothchangesbetweendifferentmotionsareachievedthroughinterpolationof endoftherstmotionwiththebeginningofthesecondmotion. Directconcatenationcanbeusedaswell,butfor non-cyclic4motionsitwillgenerateadiscontinuity atthetransition. Transitionsbetweenmotionsaremadeinterpolatingthejointcurvesparametersoveraninterpolationinterval.In[18],anapproachusingspacetime constraintsandinversekinematicswasused,generatingseamlessanddynamicallyplausibletransitions betweenmotionsegments. 4Perfectcyclicmotionsarealmostimpossibleincaptured motions,duetomeasurementerrorsandnormalhumanvariationinthecaptureprocess. Blending Blendingoperationsarenormallyusedtocombinespecialcharacteristicsofdierentmotions.For example,twokindsofwalkmotionmaybecombined toproduceanewone,blendingthejointcurvesof bothmotions.usingthisapproach,itispossibleto createawholefamilyofdierentmotions,justvaryingtheblendfactorbetweenthecurves. Inblendingoperations,theremustbespecialattentiontomotionsynchronizationandreparametrization.Synchronizationbetweenmotionscanbe achievedusingtime-markers,whichactaskinematicconstraints,matchingimportanteventsin bothmotionsthatwillbecombinedandperformingreparametrizationswhenneeded.withoutthese tools,motionblendingisuseless. Notethatconcatenationcanbeinterpretedas aparticularcaseofblendingwherelittleornooverlappingoccurs. 5TheProposedArchitecture Themotivationoftheproposedarchitectureincludes threemainobjectives: toprovideasetoftoolsformotionmanipulation andanalysis. toallowtheproductionofhigh-qualitycomplex animations,usingreusablemotionlibraries. tocompensatetechnologicallimitationsofmotioncapturehardware. Theframeworkiscomposedofbasicmodules: input,processingandoutput,eachoneresponsible foraspecicsetoftasks(gure6).thesemodules aresupportedbyagraphicaluserinterface. User Interface Input Module Processing Module Output Module Data Structures Figure6:frameworkofthearchitecture Thedatastructuresofthearchitecturerepresentstwoentities:anactorandmotions.

5 5isrepresentedbyagraphformedbyjointsandlinks. Theactoristreatedasaskeleton.Itstopology F.W.S.V.daSilva,L.Velho,P.R.Cavalcanti,J.deM.Gomes Itsgeometryisrepresentedbyseriesofconnected limbs.thisdescriptionisadequatetobeusedin amotioncaptureanimationsystem,sinceitreects sentedusingamodiedversionofzeltzer'sapj(ax- ispositionjoint)structure[13],adaptedtowork withmotioncaptureddata. Attheprogramminglevel,theactorisrepre- performer(therealactor). quisition,markersareattachedatthejointsofalive thestructureofanarticulatedgure.fordataacsitionaland/orangularvariation,sampledbythe capturehardwareduringthenumberofframesrequiredtocompletetheactor'sperformance.this Motionsarebestrepresentedascurvesintime. Normally,thecaptureddataconsistsofmarker'spo- descriptionisusedforeachdegreeoffreedom(dof) oftheactor. terpretationandpre-processingofmotiondata. 5.1InputModule Thismodulefocusesonproblemsconcerningtheinable,theremustbeawaytodenedierentskeletons,eachoneappropriatedtoreceivethedatafrom Therststepbeforeloadingamotionleis Figure7:inputmoduleframework mapped.becausethereareseveralleformatsavail- tospecifytheskeletonwherethemotionwillbe aspecicmotioncaptureleformat. denitionles(sdf),thatrelatesdierentleformatswiththeinternaldefaultskeletondenitionvidedinthearchitecturechangeitsstate,according Inotherwords,thedefaultskeletondescriptionpro- Tomaintaincompatibility,wecreatedskeletonsible,asshowningure8. motionprocessingtechniques,thereforebeingexten- modulewasdesignedtoallowtheintegrationofnew totheincomingmotiondataformat. can\llthehole",butthebestapproachistouse duetoocclusion.inthiscase,linearinterpolation whenthecamerascannottrackoneormoremarkers formation.thisusuallyhappensinopticalsystems, Sometimes,theinputdatawillhavemissingin- 5.2ProcessingModule computethejointbehaviorinthe\hole"region. predictionlters5,withbiomechanicalconstraints,to Thismodulecomprisesthesetoftoolsformotion describedinsection4. theoriginalcaptureddata,generatingnewclasses analysis,manipulationandreuse.thesetoolswere ofmotionsthatinheritthealivenessandcomplexitytypicaltothecaptureprocess.moreover,this Thegoalistoprovideecientwaystomodify5.3OutputModule Figure8:processingmoduleframework puter, Personalcommunication,LanceWilliams,AppleCom-greateort,sincetheyusethesametechnology. production. Asoutlinedbefore,motioncaptureddataportability However,therearedataformatswithdierentmark- isimportanttoimprovetheexibilityofanimation Mostdataformatscanbeconvertedwithout Motion Definition Positional Data Only? Angle Calculation Map to 3D Model Skeleton Description Internal Format yes Conversor Drop in Motion ScratchPad Motion ScratchPad no user selection Motion Operations Filtering Concatenation Blending Output composition

6 AnArchitectureforMotionCaptureBasedAnimation 6 ersarrangementornumber.inthiscase,skeleton conversionsareplausible,yetnotalwayspossible. Onealternativeistospecifyauniversaldata formatthatacceptsmostexistingfeaturesofprofessionalsystems.inthatway,motionlibrariesare easiertobemaintained.theycanbeimprovedwith newdierentmotions,comingfromvarioussources. Itisalsonecessarythattheprocessedanimation couldberenderedframebyframeusingthesystem, orevenpipedtoprofessionalrenderingsystems,like RenderMan[21]andPovRay[14]. Composition Saving Motion Curves Binary Format to disk Figure9:outputmoduleframework 5.4InterfaceModule Onemajorproblemonmostanimationsystemsis thattheydonotprovideaconcisedescriptionof basicentities,operationsandconcepts.thefunctionalityofourarchitecturewouldbelimitedbya conventionaluserinterface. Tocompletethearchitecturedescription,weintroduceaninterfacethatrepresentsthebasicstructurepresentedintheprevioussub-sections.Thisinterfaceispartoftheprototypesystem,thatwillbe describedinsection6. Wedecidedtoadoptaninterfaceparadigmused inpost-productionvideoworkstations[15].motions arerepresentedbyahorizontalbar,usingaframe rulerassociatedwithit.thisvisualdescription givesaprecisespatialandtemporalperceptionof themovement. Theuserinterfaceiscomposedofvariousgraphicalobjectsthatareorganizedinpanelsandrepresent higherleveloperations.foramoredetaileddescriptionoftheinterfaceparadigmusedintheprototype system,pleasereferto[3]. 6ThePrototypeSystem Inthissectionwepresentaprototypesystem,implementedaccordingtotheproposedarchitecture. Thissystemworkswithmotioncaptureddata, usingtheprocessingmoduletocreatenewmotions, expandingtheexistinglibrary. Specialattentionwasgiventothesystem'sGUI, whichusesadynamicapproach,withseveralwindowssharinginformationatdierentlevels.the programiscontrolledbyaloopthatchangetheinterfacecontentsaccordingtouserinteraction. Inthissystem,workwithmotionsisstraightforward:theusercanselectseveralmotionsfroma existinglibrary,andputtheminascratchpad.with afewcommands,theuserisabletoapplydierentmotionoperations,withallnecessaryinformationavailablewithinhisvisualeld. Initially,thesetofoperationsconsistsofltering,concatenation,blendingandtransition.Oneof themainobjectivesofthesystemistocontinuously integratenewmotiontools,expandingtheanimator'spossibilitiesandcreatingnewmotionswiththe existingtools.inthatway,motionselection,cropping,cutandotherhigherleveloperationscanbe addedtotheinitialset. Figure10showsasnapshotofatypicalsystemusage.Notetheinterfaceobjectsthatrepresent themotioncurvesasasampledsignal(1),andthe skeletongraphdescription(2). Window3showstheMotionScratchPad,a graphicalobjectcreatedtohelpuserinteraction withthesystem.actingasamotionorganizer,the ScratchPadprovidesusefulinformationandaglobal perceptionofthemotionsplacedonit. Motionoperationsalsohavetheirowngraphical objects.forexample,window4showsaconcatenationoperationbetweenseveralmotions. Theplaybackofanimationsisexecutedinwindow5.Acontrolpanelisintegratedwithit,providingcontrolsforinteractiveplaybackasusedinvideo recorders. 6.1ImplementationIssues Thearchitectureandprototypesystempresentedin thisworkwereimplementedintheprogramminglanguagec,usingasgiindigo2graphicworkstationas thebaseplatform.weemployedopenglforrenderingandxforms[20]forthebasicguigeneration. TheadvancedGUIobjectsweredesignedandimplementedseparately,andthenaddedtotheforms library. DuetoOpenGL'srenderingfacilitiesandto thedynamicinterfacecontrolusedinthesystem, areal-timeframerateisachievedduringtheplaybackofanimations(about15frames/secinasgi Indigo2).Theprototypesystemwasalsotestedin

7 7 F.W.S.V.daSilva,L.Velho,P.R.Cavalcanti,J.deM.Gomes framerates. thelinuxandrisc6000platforms,alsowithgood Figure10:Snapshotoftheprototypesystem. turebasedanimationsystems.usingthebuilding blockparadigm,motionscanbecombinedormodi- 7ConclusionsandFutureWork Thispaperpresentedanarchitectureformotioncap- thebehavioralfunctionscouldcontrolthepro- guideforproceduralobjects.inthesecondcase, therstcase,capturedmotionscouldactasa variousanimationtools.also,aguiwasproposed edtocreatenewmotionsandlongeranimations. problemsinherenttothecaptureprocess,providing tooeraconceptuallycorrectvisualizationofthe animationelements. Thearchitecturedealswithsometechnological combinemotioncapturewithsound.inthis cessingmodule,combiningandmodifyingcap- turedmotionstoimprovethevisualqualityof theanimation. sultsthatencourageustoimproveit. posedarchitectureandinterface,withpromisingre- Aprototypesystemwasbuilt,basedonthepro- implementationofotheradvancedmotionoperations([12],[18],[17]),comparingtheirresults thetemporaldescriptionofthesound. chronizethekeymomentsinthemotionwith case,thetime-markerscouldbeusefultosyntureworkinclude: Weplantoexpandtheexibilityoroursystem.Fu- 7.1FutureWork 8Acknowledgements andextractingconclusionsandsuggestionsfor combinemotioncapturewithproceduralanimation[22]andbehavioralanimation[23][25].in modules,improvingsystem'sexibility. capturedata,andtothebraziliancouncilforscienabs,inc.andbiovision,inc.foraccesstomotion insertionofkeyframingandinversekinematicstheauthorswouldliketothankviewpointdatal- improvementsand/ornewtechniques. atlcg/ufrj,aspartofthemasterprogrameeof inthelaboratoryofvisgrafprojectatimpaand therstauthor.thisprojectissponsoredbycnpq, ticandtechnologicaldevelopment(cnpq)forthe nancialsupport.thisresearchhasbeendeveloped

8 AnArchitectureforMotionCaptureBasedAnimation 8 FAPERJ,FINEPandIBMBrasil.Alsothanksare duetothereviewersfortheirvaluablecomments. 9References [1]Ginsberg,C.M.,HumanBodyMotionasInputtoanAnimatedGraphicalDisplay,Master Thesis,MassachusettsInstituteofTechnology, May1983. [2]Maxwell,D.R.,GraphicalMarionette:A ModerndayPinocchio,MasterThesis,MassachusettsInstituteofTechnology,June1983. [3]Silva,F.,Velho,L.,Cavalcanti,P.and Gomes,J.,ANewInterfaceParadigmforMotionCaptureBasedAnimationSystems.InProceedingsofthe8thEUROGRAPHICSWorkshoponComputerAnimationandSimulation -CAS'97. [4]FXFighter-MotionCapturevs.Keyframing Page. [5]Dyer,S.,Martin,J.,Zulauf,J.,Motion CaptureWhitePaper.TechnicalReport.SiliconGraphics,December12,1995. [6]VirtualSets.SiliconStudioFeatures.December [7]Azarbayerjani,A.,Wren,C.,Real-Time 3DTrackingoftheHumanBody.InProceedingsofIMAGE'COM96,Bordeaux,France, May1996. [8]CharacterMotionSystems. InComputer Graphics(SIGGRAPH'94),Courseno.9. [9]Mulder,S.,HumanMovementTrackingTechnology.HandCenteredStudiesofHumanMovementProject,SimonFraserUniversity.TechnicalReport94-1,July1994. [10]Silva,F,MovimentoCapturado-Introduc~ao atecnologia.relatoriointerno-laboratorio VISGRAF,IMPA,Abrilde1997. [11]O'Rourke,J.,ComputationalGeometryinC. CambridgeUniversityPress,1994. [12]Williams,L.,Brudelin,A.,MotionSignal Processing.InComputerGraphics(SIGGRA- PH'95Proceedings)(August1995),pp [13]Zeltzer,D.andSims,F.,AFigureEditor andgaitcontrollerfortasklevelanimation. InComputerGraphics(SIGGRAPH'88),CourseNotes,no.4, [14]PersistenceofVisionRay-Tracer. [15]TurboCube-User'sGuide.IMIXCompany. [16]Silva,F.,Cavalcanti,P.,Animac~oesem TempoRealUtilizandoMovimentosCapturados.InProceedingsofSIBGRAPI'96,IXBrazilianSymposiumofComputerGraphicsandImageProcessing,pp ,1996. [17]Witkin,A.andPopovic,Z.,MotionWarping.InComputerGraphics(SIGGRAPH'95 Proceedings)(August1995),pp [18]Cohen,M.,Rose,C.,Guenter,B.andBodenheimer,B.,EcientGenerationofMotion TransitionsUsingSpacetimeConstraints.In ComputerGraphics(SIGGRAPH'96Proceedings)(August1996),pp [19]OZVirtual. [20]XformsHomePage, [21]Pixar'sRenderman, [22]Perlin,K.,RealtimeResponsiveAnimation withpersonality.inieeetransactionsonvisualizationandcomputergraphics,vol1,no.1, March1995. [23]Terzopoulos,D.etal.,ArticialFishes withautonomouslocomotion,perception,behaviorandlearning,inaphysicalworld.in ProceedingsoftheArticialLifeIVWorkshop, MITPress(1994). [24]Witkin,A.andKass,M.,Spacetime Constraints. InComputerGraphics(SIG- GRAPH'88Proceedings)(August1988),pp [25]Costa,M.andFeijo,B.,AnArchitecturefor ConcurrentReactiveAgentsinReal-TimeAnimation.InProceedingsofSIBGRAPI'96,IX BrazilianSymposiumofComputerGraphicsand ImageProcessing,pp [26]Amaya,K.,Brudelin,A.,Calvert,T., EmotionfromMotion.InProceedingsofComputerAnimation(CA'96),1996.