CS 283Advanced Computer GraphicsMotion CaptureJames F. O’BrienAssociate ProfessorU.C. BerkeleyMonday, November 16, 20092Motion Capture•Record motion from physical objects•Use motion to animate virtual objectsSimplified Pipeline:Setup and calibrate equipmentRecord performanceProcess motion dataGenerate animationMonday, November 16, 20093Basic PipelineFrom Rose, et al., 1998SetupRecordProcessAnimationMonday, November 16, 2009Captures “Signature” of Actor4!"#$%&!'()*(+$",-)./0$1+*2,)*(+3045+(6(7*08"#$%&!'()*(+$",-)./0$1+*2,)*(+3045+(6(7*08'()*9,)*(+$Monday, November 16, 20095What types of objects?•Human, whole body•Portions of body•Facial animation•Animals•Puppets•Other objectsMonday, November 16, 20096Capture Equipment•Passive Optical•Reflective markers•IR (typically) illumination•Special cameras •Fast, high res., filters•Triangulate for positions Images from Motion AnalysisMonday, November 16, 20097Capture Equipment•Passive Optical Advantages•Accurate•May use many markers•No cables•High frequency•Disadvantages•Requires lots of processing •Expensive systems•Occlusions•Marker swap •Lighting / camera limitationsCapture EquipmentPassive Optical AdvantagesAccurateMay use many markersNo cablesHigh frequencyDisadvantagesRequires lots of processingExpensive (>$100K)OcclusionsLighting/camera limitationsMarker SwapMonday, November 16, 20098Capture Equipment•Active Optical •Similar to passive but uses LEDs•Blink IDs, no marker swap•Number of markers trades off w/ frame ratePhoenix Technology Phase SpaceMonday, November 16, 20099Capture Equipment•Magnetic Trackers•Transmitter emits field•Trackers sense field•Trackers report position and orientationCapture EquipmentMagnetic TrackersTransmitter emits fieldTrackers sense fieldTrackers report locationand orientationControlMay be wirelessMonday, November 16, 200910Capture Equipment•Electromagnetic Advantages•6 DOF data•No occlusions•Less post processing•Cheaper than optical•Disadvantages•Cables•Problems with metal objects•Low(er) frequency•Limited range•Limited number of trackersMonday, November 16, 200911Capture Equipment•ElectromechanicalAnalogusMonday, November 16, 200912Capture Equipment•PuppetsDigital Image DesignMonday, November 16, 2009Realtime Systems13!"#$%$&'(&)*+'*,&-./+0%$&0($12&&"#$%$&'(&)*+'*,&-./+0%$&0($123$$456&789',+$%.-+':$($++',;("#.+&.%$&+#$&'((0$(2&<$-*%1',;&+#$&1.+.&.--0%.+$56&.,1&=0'-456>+6/$(&*?&+$-#,*5*;'$(>%0,,',;&.&)*+'*,&-./+0%$&(#**+@//56',;&+#$&1.+.&+*&+#$&-#.%.-+$%>?'5+$%',;&+#$&1.+.>?'++',;&+*&.&(4$5$+*,A1'+',;&)*+'*,&1.+.&/*(+>)*%+$)>-#.,;',;&.,1&-*,-.+$,.+',;>;$,$%.5'B$1&)*+'*,&?%*)&.&1.+.C.($Monday, November 16, 2009Facial Mocap14!"#$%$&'(&)*+'*,&-./+0%$&0($12&&3.,4&5.)$(6&-./+0%$&-$7$8%'+'$(6&7'9$7':$&)*+'*,"#$%$&'(&)*+'*,&-./+0%$&0($12&&;%.',',5&.,1&<=>.-'.7&?,').+'*,Monday, November 16, 200915Performance Capture•Many studios regard Motion Capture as evil•Synonymous with low quality motion•No directive / creative control•Cheap•Performance Capture is different•Use mocap device as an expressive input device•Similar to digital music and MIDI keyboardsMonday, November 16, 2009Different Data16!"#$%&'() * + ,- $ & $ ,. /$(01(,%2$3141*&5*,2)467,87 9:)*&7,; *1)&<1(,)7,)-1$2581(,&)+<&,32:&<)*+,:(,&<)*,70)*=*,(1%1$&$ 621,>2$*-4$(07>?7)*+,7&$*-$(-,4$(01(,71&7?7)*+,4$(01(,-$&$/$+*1&)35%&)3$2!"#$%&'() * + ,- $ & $ ,. /$(01(,%2$3141*&5*,2)467,87 9:)*&7,; *1)&<1(,)7,)-1$2581(,&)+<&,32:&<)*+,:(,&<)*,70)*=*,(1%1$&$ 621,>2$*-4$(07>?7)*+,7&$*-$(-,4$(01(,71&7?7)*+,4$(01(,-$&$/$+*1&)35%&)3$2Monday, November 16, 2009Auto Calibration1755Torso (Root)PelvisHeadUpper ArmLower ArmHandUpper LegLower LegFootFigure 2: Example of an articulated hier archy that could beused to model a human figure. The torso is the root body and thearrows indicate the outboard direction. For rendering, the skele-ton model shown here would be replaced wi th a more realisticgr aphical model.A transformation Ti→jconsists of an additive, length 3 vec-tor co mp o n en t, ti→j, and a multiplicative, 3 × 3 matrix compo-nent, Ri→j. We will refer to ti→jas the translational compo-nent of Ti→jand to Ri→jas the rotational compon en t of Ti→j,although in general Ri→jmay be any invertible 3 × 3 matrixtransformation.A point, xi, expressed in the i-th coordinate system may thenbe transformed to the j-th coordinate system byxj= Ri→jxi+ ti→j. (1)A transformation from the i-th coordinate system to thej-t h coordinate system may be inverted so that given Ti→j,Tj→imay be computed byRj→i= (Ri→j)−1(2)tj→i= (Ri→j)−1(−ti→j), (3)where ( ·)−1indicates matrix inverse.Because in general the bodies are in motion with respect toeach other and the world coordinate system, the transformationsbetween coordinate systems change over time. We assume thatthe motion data is sampled at n discrete momen ts in time calledframes, and use Ti→jkto refer to the value of Ti→jat framek ∈ [0..n − 1].An articulated hierarchy is described by the topological infor-mation indicating which bodies are con n ected to each other andby geometric information indicating the locations of the con-necting joints. The topological information takes the form of atree1with a single body located at its root and all other bodiesappearing as nodes within the tree as shown in Figure 2. Whenreferring to directions relative to the arrangement of the tree, theinboard direction is towards the root, and the outboard directionis away from the root. Thus for a joint connecting two bodies, iand j, the parent body, j, is the inboard body and the child, i, isthe outboard body. Similarly, a joint which conn ects a body toits parent is that body’s inboard joint and a joint connecting the1We discuss the topological cycles created by loop joints in Section 5.ciliInboard body, j=P(i)Outboard body, iOrigin of CjOrigin of CiJoint iFigure 3: Joint diagram showing the location of the rotaryjoint between bodies i and j = P (i). The location of the joint isdefined by a vector displacement, ci, relative to the coordinatesystem of body i, and a second vector displacement, li, in thecoordinate system of body j.body to one of its children is an outboard joint. All bodies ha veat most one inboard joint but may ha ve multiple outboard joints.The hierarchy’s topology is defined using a mapp ing function,P (·), that maps each body to its parent body so that P (i) =j will imply that the
View Full Document
Unlocking...