Spatial Keyframing for Performance-driven Animation

Transcription

1 Eurographs/ACSIGGRAPH Symposum o Computer Amato (25) K. Ajyo, P. Faloutsos (Edtors) Spatal Keyframg for Performae-drve Amato T. Igarash,3, T. osovh 2, ad J. F. Hughes 2 The Uversty of Tokyo 2 Brow Uversty 3 PRESTO, JST Abstrat Ths paper trodues spatal keyframg, a tehque for performae-drve harater amato. I tradtoal temporal keyframg, key poses are defed at spef pots tme:.e., we defe a map from a set of key tmes to the ofgurato spae of the harater ad the exted ths map to the etre tmele by terpolato. By otrast, spatal keyframg key poses are defed at spef key postos a 3D spae where the harater lves; the mappg from the 3D spae to the ofgurato spae s aga defed by terpolato. The user otrols a harater by adjustg the posto of a otrol ursor the 3D spae; the pose of the harater s gve as a bled of earby key poses. The user thus a make expressve moto real tme ad the resultg moto a be reorded ad terpreted as a amato sequee. Although smlar deas are preset prevous systems, our system s uque that the desger a qukly desg a ew set of keyframes from srath, ad make a amato wthout moto apture data or speal put deves. Our tehque s espeally useful for magary haraters other tha huma fgures beause we do ot rely o moto-apture data. We also trodue several applatos of the bas dea ad gve examples showg the expressveess of the approah.. Itroduto The most popular approah to harater amato s keyframg, where the desger maually spefes the pose of a harater as a dsrete set of frames (keyframes) ad the omputer sytheszes the poses the remag frames. However, ove users have dffulty reatg flud moto usg ths approah ad t s very labor-tesve work. Other approahes suh as moto apture ad physally based smulato are avalable, but they are expesve to use ad are ot sutable for desgg expressve magary motos. Furthermore, moto apture s maly desged for huma fgures ad s ot dretly applable to magary haraters. We desrbe here a method that lets ove users reate lvely amatos for arbtrary 3D haraters qukly ad easly usg a stadard put deve suh as a mouse. The bas dea s to dretly reord the user's performae or atos, that s, the user's dret mapulato of the harater. We beleve that ths s muh faster ad more tutve tha tradtoal temporal keyframg, beause the user eed ot metally traslate stat keyframes to temporal moto durg desg. I performae-drve amato, what you perform ad see o the sree durg reordg s what you obta as the fal result. Fgure : Spatal keyframg wth sx key poses (top) ad a example amato sequee usg t (bottom). The user assoates eah pose wth a loato spae (yellow markers) a preparato phase. Durg performae, the user moves the otrol ursor (red sphere) ad the system sytheszes a amato sequee by bledg earby poses. The Eurographs Assoato 25

2 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato The problem s that t s dffult to otrol omplated moto of a harater real tme usg stadard put deves. A harater may have may degrees of freedom (DOFs), ludg posto, oretato, ad agles at may jots, whle a typal put deve has oly two DOFs. To otrol may DOFs real tme wth put deves wth lmted DOFs, our system takes several predefed key poses ad bleds them real tme durg performae. I a preparato phase, the user reates several key poses ad assoates them wth spef postos the 3D spae (whh we all spatal keyframes). Durg performae, the user moves a otrol ursor the 3D spae ad the system sytheszes a orrespodg pose by bledg earby spatal keyframes (Fgure ). Sytheszg ew poses by bledg predefed poses s already ommo prate, ad makg amatos from real-tme performae s ot ew. The ma otrbuto of ths paper s to ombe these methods a pratal system for makg lvely harater amatos from srath wthout moto-apture data or speal put deves. Ths paper also desrbes spef methods for bledg poses to obta reasoable results wth very sparse key poses, as well as several extesos to the bas dea. We hope that ths paper eourages the use of performae-drve approahes for harater amato. The resultg amatos are very dfferet from those reated usg tradtoal methods, as they make apparet the amator's atural sese of tmg. It s also muh easer ad more fu to reate amatos ths way. 2. Related work Performae-drve amato ad puppeteerg usually rely o a spealzed put deve or a moto-apture system [Stu98]. The dret mappg they assg betwee the harater's DOFs ad the deve's DOFs requres a sgfat amout of trag ad expertse to otrol fluetly. Sh et al. [SG] trodued methods for retargetg a moto-aptured performer's full body moto to haraters of dfferet szes. Dotheva et al. [DYP3] proposed layered atg, where the user desgs omplated motos by multple atg passes. Our goal s to make performae-drve amato more aessble to asual users who lak expesve deves. Sytheszg ew poses by bledg predefed poses s already doe may amato systems, but most of them are desged for large amouts of moto-apture data. Wley ad Hah [WH97] assoated key poses obtaed by moto apture to a dese grd of pots spae ad learly terpolated them. Rose et al. [RBC98] terpolated moto-apture sequees usg radal bass futos to express the harater's emotos. Kovar ad Gleher's system [KG4] automatally ostruts a parameterzed spae of motos by aalyzg large amouts of moto data ad sytheszes a ew pose by weghed terpolato of earby poses. Our system s desged to work wth very few key poses ad does ot requre a large moto data set. Oe work losely related to ours s the artst-dreted verse kemats of Rose et al. [RSC]. They also used radal bass futos to terpolate sparse examples spae. Our goal dffers from thers that we fous o performae-drve amato authorg from srath, whle ther fous was o otrollg pre-authored moto data. There are other related teratve systems for amato. Ngo et al. [NCD*] used lear terpolato for mapulatg 2D vetor graphs. Key poses are embedded a speal struture alled a smplal ofgurato omplex. Rademaher [Rad99] used terpolato for otrollg vew-depedet geometry. Key geometres are assoated wth spef vew dretos ad are bleded aordg to the urret vew dreto. aszlo et al. [vpf] ombed teratve harater otrol wth physs-based smulatos. They showed a example whh the horzotal ad vertal motos of the mouse were dretly mapped to the harater's dvdual DOFs. The "moto doodle" system lets the user sketh the teded moto path; the system the sytheszes a approprate moto by ombg pre-authored keyframe amatos [TBvP4]. Terra ad etoyer used performae for tmg preauthored key frame amato [T4]. Doald ad Hele proposed to use a hapt put deve to mapulate moto apture data [DH]. 3. The User Iterfae Our system ossts of two subsystems. Oe s for desgg spatal keyframes ad the other s for makg amato usg these keyframes. 3. Desgg spatal keyframes The user's frst task s to desg a set of spatal keyframes, that s, to set poses of a harater ad assoate them wth postos the 3D spae. The user frst mports a 3D artulated model to the system. We provde a stadard dret-mapulato terfae for the 3D model. The user a hage the posto of the harater by draggg t wth the spae ad hage ts pose by rotatg ts parts; the objet a also be moved parallel to the groud by draggg ts shadow [HZR*92]. Oe the user s satsfed wth a pose, the ext task s to mark t as a ew spatal keyframe by assoatg t wth a posto the 3D spae. To do so, the user moves the red otrol ursor to the target posto ad presses the "set" butto. A small yellow ball ow appears at the loato of the otrol ursor that dates the exstee of the spatal keyframe. A spatal keyframe ossts of two elemets: () a harater pose (e.g. jot agles) ad (2) the xyz ursor posto that orrespods to that pose. The user defes a set of these spatal keyframes by repeatg the above proess ad these keyframes defe a mappg from the otrol spae to the set of the harater's poses va a terpolato proedure desrbed the ext seto. The user a ex- The Eurographs Assoato 25.

3 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato ame ths mappg at ay tme by draggg the otrol ursor wth the rght mouse butto dow: the system bleds the eghborg spatal keyframes aroud the otrol ursor ad otuously dsplays the result. Ths sythess s ot doe whe the left mouse butto s used; the left butto s reserved for settg ew poses. The mportat feature of the system s that the user a set spatal keyframes at arbtrary postos the 3D spae, ad that the user a start testg terestg motos wth very few spatal keyframes. Wth oly three keyframes, the user a make terestg full body moto, as show Fgure 2. Ths s otrast to lear terpolato systems that requre may keyframes spefed a grd struture [WH97; NCD*]. Note that the spatal keyframes are overlayed the same 3D spae habted by the harater. Ths s otrast to Ngo et al. s system [NCD*] whh keys are plaed a speal ofgurato spae. Ths makes t possble to establsh a tutve orrespodee betwee the loato of a spatal keyfmrame ad the assoated pose. For example, the keyframe for "look left" s lkely to be o the left sde of the sree ad "look rght" o the rght (as Fgure 2). Ths tutve mappg may be dffult to aheve whe usg automat mappg suh as the method trodued [GH4]. Fgure 2: A smple example wth three key poses. Three key poses are assoated wth the three yellow balls (left). As the user drags the red otrol ursor wth the rght mouse butto dow, the system sytheszes a ew pose by bledg the three (rght). Note that may jot agles as well as the harater's posto are otrolled together. 3.2 akg amato by performae Havg set the eessary spatal keyframes, the amator a use them to beg performg amatos. I ths phase, the harater's pose a o loger be adjusted dretly. The user moves the otrol ursor ad the system shows the sytheszed pose o the sree (Fgure 3). Reordg starts whe the user starts draggg the otrol ursor after pressg the "reord" butto ad fshes whe the mouse butto s released. The user a wath the resultg moto mmedately by pressg the "play" butto, ad a wath t from ay dreto by hagg the amera posto. Fgure 3: Jugglg. The user frst sets the e key poses as show o the left. As the user drags the otrol ursor, the harater performs a smooth moto as show o the rght. 3.3 Dsusso I the urret system a 2D mouse s used to otrol the posto of the 3D otrol ursor ad the otrol ursor moves parallel to the sree durg draggg, so the moto of the 3D otrol ursor s atually 2D moto. Although terestg amatos a be desged wth ths setup, we pla to vestgate the possblty of usg 3D put deves. Three-dmesoally dstrbuted key poses may also be helpful for srptg purposes whe spefyg the 3D moto of the otrol ursor (see Seto 5.3). Desgg amatos ths way s really tutve ad fast. The spatal keyframe examples ths paper took oly to 2 mutes to desg. Ths ludes several teratos to adjust the resultg moto. After settg the keyframes, the oly thg the user eeds to do s to drag the otrol ursor. There s o eed to dretly edt eah frame or repeat performae, as s requred layered atg [DYP3]. The tme eessary to make a amato sequee s the same as the tme to play t. I addto, the resultg moto s very lvely beause the user's dret had moto s (dretly) preset the amated moto. Ths s otrast to the uatural, robot moto desged by ove users usg stadard keyframg. Ths dea s smlar sprt to the tehque trodued by Terra ad etoyer [T4], but they used performae to adjust oly the tmg of a predefed keyframe amato whle our system allows the user to otrol tmg ad pose smultaeously. A possble oer s that eah mappg s usually spef to a sgle moto ad thus ot very reusable. Ths s true to some extet; the mappg defed for jugglg makes lttle sese for other motos. However, our method allows the user to easly expermet wth ad desg a wde varety of motos wth a spef lass of moto, e.g. jugglg the user a move the ball fast or slowly, hgh or low, lokwse or at-lokwse. Ths flexblty s mssg tradtoal temporal keyframg methods ad s rtal for desgg ovg motos. 4. Algorthm Ths seto desrbes the algorthm we use the urret mplemetato. Note that the ma purpose of the followg desrpto s to provde the eessary formato to mplemet the system, ot to propose a better algorthm The Eurographs Assoato 25.

4 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato for moto bledg. The bledg of moto s essetally a dffult problem. ay tehques have bee proposed, suh as quatereos ad the expoetal map, eah wth ts ow stregths ad weakesses. We hose ths partular method beause t s easy to mplemet, works well prate, ad satsfes erta reasoable user expetatos It s our future work to mplemet ad ompare other approahes detal. The system takes the xyz-oordates of the otrol ursor ad a set of spatal keyframes (the xyz-oordates of ahors ad assoated harater poses) as put ad returs a bleded harater pose. A pose s defed as a set of loal trasformatos of the body parts. We urretly do ot allow traslato for ay part exept the root, so we have 3 3 rotato matres for all parts ad oe xyz traslato vetor for the root part. We terpolate eah etry of the matrx usg a radal bass futo ad orthoormalze the resultg matrx. 4. Iterpolato usg a radal bass futo Radal bass terpolato s useful for sattered data terpolato [Powell87]. We use the terpolato method desrbed by Turk ad O'Bre [TO2]. Eah etry of eah matrx s treated as a real-valued futo o the otrol spae, expressed the form j f ( x ) = = d j Φ( x j ) + j= P( x ) where F(x) s a radal bass futo, j are the marker postos, d j are the weghts, ad P(x) s a degree-oe polyomal. We urretly use F(x) = x as a bass futo. We hose ths futo emprally after several expermets, largely beause the terpolato result follows the otrol ursor most fathfully. Other futos are smoother but show some osllato effets. The system solves for values d j suh that f(x) represets the gve pose at the marker loatos: supposg h j =f( j ), the ostrat s represeted as j h = = d jφ( j ) + P( ) j= Se ths equato s lear wth respet to the ukows, d j ad the oeffets of P(x), t a be formulated as the followg lear system: Φ Φ x y z Φ Φ x y z z d h z d h p = p p2 p3 x y x y where x y z = (,, ), Φ = Φ ), j ( j P( x ) = p + px + p2 y + p3z. We obta the terpolato futo f(x) by solvg the above lear system. We eed to solve the lear system for eah etry of the 3 3 rotato matrx. However, the large oeffet matrx o the left had sde of the above equato s detal for all e etres, so we oly eed to vert the large matrx oe for eah jot. For the root part, we also ompute eah etry of the traslato vetor usg ths method. Speal are must be take whe there are fewer tha four spatal keyframes ad whe the spatal dstrbuto of the markers s degeerate (learly or two-dmesoally dstrbuted). I these ases, we apply the terpolato a spae of redued dmesos by mappg the marker loatos to the redued spae before applyg the above proedure. The dmeso of P(x) s also redued aordgly. The hoe of F(x) must also hage to obta true thplate terpolato [TO2], but we urretly use F(x) = x for all dmesos ad t works well. 4.2 Orthoormalzato The terpolated matrx obtaed by the above proedure s ot geeral a orthoormal rotato matrx; we eed to orthoormalze t. I some methods for orthoormalzato suh as Gram-Shmdt, the result s ot eessarly lose to the orgal matrx. We urretly use the followg teratve refemet method to orthoormalze the matrx by matag the balae betwee the three axes (Fgure 4). Suppose we have three bass vetors x r, y r, z r ad wat to orthoormalze them. We frst ormalze them. We the ompute r r r u = y z, r r r v = z x, r r r w = x y ad ormalze these. The we ompute r r r x = ( x + u ) / 2, r r r y ( ) / = y + v 2, r r r z ( )/ = z + w 2 ad ormalze them. We repeat the above proedure utl the resdual r r ( ) 2 r r ( ) 2 r r r = x ( ) 2 y + y z + z x s below a threshold or the umber of repetto exeeds a predefed out. We urretly use. for the resdual threshold ad for the out. It usually takes fewer tha 3 teratos to obta vsually pleasg results. The maxmum umber,, s suffet to detet a degeerate ase. Fgure 4: Orthoormalzato proess. The system gradually makes the bass vetors perpedular to eah other. The Eurographs Assoato 25.

5 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato The above method s emprally desged wth the goal of obtag reasoable results robustly ad qukly wth a smple mplemetato. The outome s satsfatory our experee. It does ot work for degeerate ases suh as r r r r x = y = z = that a arse, for example, whe the otrol ursor s the mddle of two key poses that fae ompletely opposte dretos. I that ase, the overgee fals ad a skewed result s show o the sree. Degeerate ases lke ths are uavodable whe reatg a suffetly e mappg from 2-spae or 3-spae to the rotato group ( Suffetly e ths ase meas that f two otrol pots orrespod to earby rotatos, the the le segmet betwee them must orrespod to a path ear the geodes path betwee these two rotatos, whh s meat to math user expetatos). However, the aswer s ot well defed ayway suh ases from the user s pot of vew. The user aturally uderstads the exstee of the degeeray ad avods t durg performae. The method also has the e mathematal property that f R s a rotato ad s a small perturbato to R that s orthogoal to the mafold of rotato matres, osdered as a submafold of the mafold of all 3 3 matres, the our proess, appled to R + t, yelds a matrx that agrees wth R to seod order t,.e., t s esetally a orthogoal projeto oto the rotato group, a property ot shared by Gram-Shmdt, for stae, as a be see by perturbg the detty by a small multple of. 4.3 Why ot agular parameterzato? Oe mght ask why we do ot use agular parametrzatos suh as euler agles, quateros [Sho85], or the expoetal map [Gra98] for the terpolato. Our short aswer s that our doma s three-dmesoal spae ad ot sequetal tme, as s ofte the ase whe the typal terpolato happes. We desrbe two example ssues that arse ths doma. Note that we oly lam here that straghtforward applato of other approahes does ot work well our target doma. It may be possble to obta smlar results to ours by elaboratg agular parameterzatos [PSS2][BF]. We leave further dsusso to future publatos. The frst ssue s that smple agular parameterzato does ot behave as expeted for extrapolato our system (Fgure 5). Suppose we have the two keyframes o the left. As we move the otrol ursor to the rght, the head otues to tur f we use agular parameterzato. I otrast, our method aturally keeps the head lookg at the ursor. Ths s a desg ssue rather tha a theoretal problem, but the bas dea behd spatal keyframg s to assoate the pose wth a posto spae ad agular parameterzato breaks the atural mappg. Key Poses Sythess Result degrees 3 degrees 8 degrees? Fgure 5: A example sythess result wth straghtforward agular parameterzato. As the user drags the otrol ursor, the harater rotates otuously. Wth our approah the harater approprately looks at the otrol ursor. The seod ssue s that there s a dsotuty whe a part rotates 36 degrees. Whe usg euler agles, the dsotuty s apparet. Eve whe usg quateros, the pose at degrees ad 36 degrees are loated at opposte poles of the ut sphere 4D spae. Ths s ot a problem whe usg a lear parameter spae suh as tme, but we are workg two- or three-dmesoal otuous parameter spae. Fgure 6 shows what happes whe we apply agular parameterzato avely. Suppose we have the four spatal keyframes show o the left. If we move the otrol ursor betwee the frst ad last marker, the resultg pose s somethg betwee the seod ad thrd key pose o the left, beause there s a dsotuty agular parameter spae betwee the frst ad last spatal keyframe. It mght be possble to desg methods that avod ths problem by elaboratg o agular parameterzato, but we beleve that our approah (dretly terpolatg the rotato matrx) s more straghtforward ad easer to mplemet for our partular applato doma. Key Poses Sythess Result degrees 3 degrees 8 degrees 27 degrees 35 degrees? Fgure 6: Aother sythess result whe usg straghtforward agular parameterzato. If we have the four key poses show o the left ad plaes the otrol ursor at the plae as show o the rght, the result s the bled of the four agles as show o the rght. Our system returs atural results by terpolatg eah ompoet depedetly. Prevous pose terpolato systems used agular parameterzato [WH97; RSC]; ths was a reasoable deso beause these systems were desged prmarly to bled exstg motos ad the problems desrbed above do ot arse. However, our goal s the reato of a ew moto from srath by performae ad t s rual to be able to support dyam behavor suh as that show Fgure. The Eurographs Assoato 25.

6 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato 5. Extesos Ths seto desrbes some extesos to the bas framework. These extesos are applatos of exstg deas for spatal keyframg ad we do ot lam sgfat ovelty here. We desrbe them here order to show the possbltes of our tehque ad to spre further explorato. 5. Iverse kemats Iverse kemats (IK) s the proess of determg the jot ofgurato requred to plae a partular part of a artulated harater at a partular loato spae. The most popular approah s to remetally update the jot agles to satsfy the gve ostrats usg Jaoba terato [G 85; WW92]. I other words, the system gradually pulls the grabbed part to the target loato. Ths meas that the resultg pose s depedet o the prevous pose, whh a easly lead to very uatural poses. ay solutos to ths problem have bee proposed, for stae usg bomehas kowledge [GG96], ostrat solvg [YN3], ad example-based optmzato [GH4]. However, they requre maual eodg of varous lowlevel ostrats or large moto-apture datasets. Furthermore, t s dffult to lude artst otrol the proess. Our spatal keyframg a be useful addg artst otrol to the verse kemats proess. The algorthm s very smple. Istead of startg Jaoba-based refemet from the prevous frame, we start the proess from the sythess result usg spatal keyframg (Fgure 7). Ths makes the resultg pose very stable. Regardless of the pose the prevous frame, the resultg pose s always the same for a gve otrol ursor posto. Our method a be see as a subset of the oe preseted Rose et al. [RSC]. A smlar tehque s also used [YKH4]. spatal keyframes (as Fgure ), but a log travelg sequee, suh as walkg, requres too may spatal keyframes. Oe way to address ths ssue s to automatally hage the harater's posto wth respet to ts body moto. We were spred by teratve harater otrol by aszlo et al. [vpf], whh the user otrols the harater's lmbs ad the loomoto s geerated as a result of a physally-based smulato. We would lke to test smlar physally-based smulato the future, but urretly use a smple rule to geerate horzotal posto hage from the harater's poses; at eah pot tme, the lowest pot of the harater s fxed relatve to the groud, ad the harater's base posto sldes to satsfy the ostrat [OTH2] (as t s too tme-osumg to hek all vertes, we maually mark the tp of eah toe beforehad ad use these marks for omputg loomoto). Whe the lowest part s above the groud, the base posto travels aordg to erta; the system remembers the horzotal travelg speed just before the lowest pot leaves the groud ad otues to slde the groud wth the same speed utl aother pot touhes the groud. The amera s fxed relatve to the harater's base posto durg reordg. It s possble that some pot o the free leg dps lower tha the supportg leg. I ths ase, the otat pot suddely swth, ausg the harater to start movg bakwards. Ths problem a be serous f we osder all vertes of the mesh as possble otat pots, but we a avod most of the problem by usg maually marked vertes oly. I prate, we do experee some waddlg moto whe reatg varous walkg motos, but the result s aeptable for ove users to qukly reate smple amatos. It s also very easy to teratvely fx the problem by adjustg key poses ad ursor trajetory whe a problem ours. Fgure 7: Ital pose (left), stadard IK result (mddle) ad IK wth spatal keyframg (rght). Stadard IK a produe very strage poses after otuous operato. I otrast, IK wth spatal keyframg returs stable results regardless of prevous pose. 5.2 oomoto Bas spatal keyframg s desged for otrollg the harater's pose at a fxed base posto, ad does ot work well for amato volvg travel or loomoto. The user a ertaly represet a small postoal hage by settg the harater dfferet plaes as depedet Fgure 8: Walkg. Four key poses (top) ad a walkg amato usg them (bottom). Observe that the groud sldes alog wth the foot o the groud. The Eurographs Assoato 25.

7 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato Fgure 8 shows a example. It has four key poses that represet a walkg yle. As the user moves the otrol ursor outerlokwse, the harater makes a walkg moto ad the groud sldes wth the lower foot. The faster the user moves the ursor, the faster the groud sldes, esurg that foot-skatg artfats do ot our. Fgure 9 shows aother example. The three key poses represet a gallopg moto. The system sldes the groud to smulate erta whe the harater s the ar. 6. Implemetato ad Results The urret prototype system s mplemeted Java (JDK.4) ad uses DretX8 for 3D rederg. It urretly uses artulated 3D models osstg of multple rgd parts embedded a herarhal struture. Freeform surfaes guded by embedded boes are ot urretly supported, but t s straghtforward to apply spatal keyframg to suh boe strutures. We use a exteso to the Teddy system [IT99] as a prmary 3D modelg system, whh the user a desg a pated artulated 3D harater very rapdly (~ mutes). Fgure ad Fgure show example amatos desged by the author. Atg wth spatal keyframg s useful for expressg the haraters' rh emotos these smple atos. Fgure 9: Gallopg. Three key poses (top) ad a gallopg amato usg them (bottom). Observe that the groud sldes alog wth the foot o the groud. 5.3 Srptg We developed spatal keyframg prmarly for teratve puppetry ad amato authorg by dret performae. However, the etral dea behd t s to reate a ompat, low-dof represetato for hgh-dof harater poses, whh should be useful for applatos other tha dret mapulato va a otrol ursor. Oe possblty s to use smple srptg for amato authorg. Whe usg srpts to otrol a stadard artulated harater, dvdual jot agles must be spefed expltly. But usg spatal keyframg, oe a otrol rh harater movemet just by spefyg the behavor of the otrol ursor a srpt. Srptg wth spatal keyframg s also useful for otrollg mutually teratg haraters. We mage that a set of spatal keyframes would be desged for eah harater, ad that they would be pakaged together (lke the model ad "rggg" of haraters amato studos). The, the srpt authors would mport the harater wth the spatal keyframe set ad start wrtg srpts that selet approprate spatal keyframes ad otrol the otrol ursor. I tradtoal srptg systems authors usually dretly spefy eah jot agle [CDP], so the spatal keyframe tehque a sgfatly lower the bar ad erh the resultg amatos. Ths s smlar to a bled-shape terfae where a harater model s shpped wth may adjustable otrol parameters, but our spatal keyframg s uque that the otrol ursor lves the same spae as the harater. Shakg Noddg Noddg 2 Fgure : A example amato. Usg the sx key poses (top), oe a desg a amato sequee whh the bear shakes hs head, makes a small od, ad makes a large od tur seamlessly. Fgure shows a example of a hghly artulated harater. We expermeted wth varous motos ad foud that our algorthm works well for these kds of haraters espeally whe the target amato s a geeral whole body moto suh as dag ad gesturg. If the target amato requres prese plaemet of edeffetors, t mght be better to terpolate the posto of the ed-effetors frst ad the apply verse kemats as [YKH4]. It s our future work to mplemet ths ad ompare the results. Fgure : A example of a hghly artulated harater. We have asked two professoal artsts to try the prototype system, oe wth extesve experee 3D graphs The Eurographs Assoato 25.

8 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato ad the other maly 2D amatos. They both uderstood the oept qukly ad started reatg amato wth 3 mutes. Examples are show Fgure 2 ad 3. They ommeted that the system was fu to use ad the experee was very ovel. However, the urret mplemetato s stll prelmary ad the test revealed ts lmtatos. The 2D artst had dffulty settg dvdual poses wth a mouse. Both wated a mehasm to prepare multple sets of spatal keyframes for dfferet motos ad swth from oe moto to aother to reate meagful stores. They oted that the system mght ot be mmedately useful for professoal produto beause they eed prese otrol for eah frame. They suggested that the system ould be useful for real-tme performae frot of audees ad for ove users. Fgure 2: A example spatal keyframes desged by a 3D expert wth experee usg stadard keyframg. He foud that spatal keyframg s muh more fu to use, ad that the resultg moto s very dfferet from those reated usg exstg methods. Fgure 3: A example amato reated by a 2D artst. He foud the system very fu to play wth ad sprg but also foud that t s stll dffult to spefy dvdual 3D poses wth a mouse. 7. mtatos ad Future Work The ma lmtato of our tehque s that spatal keyframg s ot dretly applable to some kds of motos. It s very atural ad effetve for motos that are sematally assoated wth spef pots spae, suh as gazg ad objet mapulato, but s dffult to apply to more omplated motos suh as speakg sg laguage. Aother problem s that spatal keyframg a represet oly oe type of moto at a tme. We foud that reasoably terestg amatos a be desged wth a sgle set of spatal keyframes by arefully dstrbutg the key poses spae, but there ertaly s a lmt. To address these problems, we pla to vestgate mehasms for ombg multple spatal keyframe sets ad ahevg smooth trastos betwee them. How well a typal user a remember the dfferet mappgs s stll a ope questo whh we hope to aswer future researh. Spatal keyframg a easly be ombed wth exstg methods for amato authorg. Oe a desg more omplated moto by usg spatal keyframg layered atg [DYP3]. It s also straghtforward to ombe t wth teratve physally based smulato to geerate realst moto automatally [vpf]. oto doodles a be used to spefy the trajetory of the harater's loomoto whle usg spatal keyframg to otrol ts pose [TBvP4]. Spatal keyframg a be see as supplemetal formato added to a rgged harater; sklled desgers desg a 3D harater wth predefed spatal keyframg ad ed users qukly author ther ow moto wth t. We pla to develop tools to support wdespread use of ths framework. Examples lude plug-s for ommeral 3D modelg ad amato systems, 3D amato players that supports spatal keyframg, ad a lbrary of 3D artulated haraters wth pre-authored spatal keyframes. Referees [BF] BUSS, S.R., FIORE, J.: Spheral Averages ad Applatos to Spheral Sples ad Iterpolato, AC Trasatos o Graphs, 2, 2, (2), [CDP] COOPER S., DANN W., PAUSCH R.: Ale: A 3-D Tool for Itrodutory Programmg Coepts. Joural of Computg Sees Colleges, 5, 5 (2), 7-6. [DH] DONAD, B. R., HENE, F.: Usg hapt vetor felds for amato moto otrol. I Proeedgs of IEEE Iteratoal Coferee o Robots ad Automato, (2). [DYP3] DONTCHEVA., YNGVE G., POPOVIC' Z.: ayered Atg for Charater Amato. AC Trasatos o Graphs, 22, 3 (23), [GG96] GUAPAI V., GEFAND J. J., ANE S. H.: Syergy-based earg of Hybrd Posto/Fore Cotrol for Redudat apulators. I Proeedgs of IEEE Robots ad Automato Coferee, (996), [G85] GIRARD., ACIEJEWSKI A. A.: Computatoal odelg for the Computer Amato of egged Fgures. I Computer Graphs (Proeedgs of AC SIGGRAPH 85), 9, 3 (985), [GH4] GROCHOW K., ARTIN S.., HERTZANN A. POPOVIC' Z.: Style-based Iverse Kemats. AC Trasatos o Graphs, 23, 3 (24), The Eurographs Assoato 25.

9 T. Igarash, T. osovh, ad J. F. Hughes / Spatal Keyframg for Performae-drve Amato [Gra98] GRASSIA, F. S.: Pratal parameterzato of rotatos usg the expoetal map, Joural of Graphs Tools arhve, 3, 3, (998), [HZR*92] HERNDON K. P., ZEEZNIK R. C., ROBBINS, D. C., CONNER, D. B. SNIBBE, S. S., VAN DA A.: Iteratve Shadows. I Proeedgs of UIST 92, (992), -6. [IT99] IGARASHI T., ATSUOKA S., TANAKA, H.: Teddy: A Skethg Iterfae for 3D Freeform Desg. I Proeedgs of AC SIGGRAPH 999, AC Press / AC SIGGRAPH, os Ageles, Ed., Computer Graphs Proeedgs, Aual Coferee Seres, AC, (999), [KG4] KOVAR., GEICHER.: Automated Extrato ad Parameterzato of otos arge Data Sets. AC Trasatos o Graphs, 23, 3 (24), [vpf] ASZO J., VAN DE PANNE,., FIUE, E.: Iteratve Cotrol for Physally-based Amato. I Proeedgs of AC SIGGRAPH 2, AC Press / AC SIGGRAPH, Ed., Computer Graphs Proeedgs, Aual Coferee Seres, AC, 2, [NCD*] NGO T., CUTRE D., DANA J., DONAD B., OEB., ZHU S.: Aessble Amato ad Customzable Graphs va Smplal Cofgurato odelg. I Proeedgs of AC SIGGRAPH 2, AC Press / AC SIGGRAPH, Computer Graphs Proeedgs, Aual Coferee Seres, AC, [OTH2] OORE, S., TERZOPOUOS, D., HINTON, G.: A desktop put deve ad terfae for teratve 3D harater amato, Proeedgs of Graphs Iterfae 22, (22), [Pow87] POWE. J. D.: Radal Bass Futos for ultvarable Iterpolato: A Revew. I Algorthms for Approxmato, J. C. aso ad. G. Cox, Eds. Oxford Uversty Press, Oxford, UK, (987), [PSS2] PARK, S. I., SHIN, H. J., SHIN, S. Y.: O-le oomoto Geerato Based o oto Bledg, I Proeedgs of Symposum o Computer Amato, (22), 5-. [Rad99] RADEACHER P.: Vew-Depedet Geometry. I Proeedgs of AC SIGGRAPH 999, AC Press / AC SIGGRAPH, Computer Graphs Proeedgs, Aual Coferee Seres, AC, (999), [RBC98] ROSE C., BODENHEIER B., COHEN.: Verbs ad Adverbs: ultdmesoal oto Iterpolato Usg Radal Bass Futos. IEEE Computer Graphs ad Applatos 8, 5 (998), [RSC] ROSE III C. F., SOAN P.-P. J., COHEN. F.: Artst-Dreted Iverse Kemats Usg Radal Bass Futo, Iterpolato. Computer Graphs Forum, 2, 3 (2), [SGS] SHIN H. J., EE J., GEICHER., SHIN, S. Y.: Computer Puppetry: A Importae-Based Approah. AC Trasatos o Graphs, 2, 2 (2), [Sho85] SHOEAKE, K.: Amatg Rotatos wth Quatero Curves. I Computer Graphs (Proeedgs of AC SIGGRAPH 85), 9, 3 (985), [Stu98] STURAN, D. J.: Computer Puppetry. IEEE Computer Graphs ad Applatos, 8, (998), [TBvP4] THORNE., BURKE, D., VAN DE PANNE.: oto Doodles: A Iterfae for Skethg Charater oto. AC Trasatos o Graphs, 2, 3 (24), [T4] TERRA S.C.., ETOYER R.A.: Performae tmg for keyframe amato. I Proeedgs of SCA 24, (24), [TO2] TURK G., O'BRIEN J. F.: odellg wth Implt Surfaes That Iterpolate. AC Trasatos o Graphs, 2, 4 (22), [WH97] WIEY D.J., HAHN J.K.: Iterpolato Sythess of Artulated Fgure oto. IEEE Computer Graph ad Applatos, 7, 6 (997), [WW92] WATT A., WATT.: Advaed Amato ad Rederg Tehques: Theory ad Prate. Addso- Wesley, 992. [YKH4] YAANE,., KUFFNER, J. J., HODGINS, J. K.: Sytheszg amatos of huma mapulato tasks. AC Trasatos o Graphs, 23, 3 (24), [YN3] YAANE K., NAKAURA Y.: Natural oto Amato Through Costrag ad Deostrag at Wll. IEEE Trasato o Vsualzato ad Computer Graphs, 9, 3 (23), The Eurographs Assoato 25.