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Motion Capture

Motion Capture. Animation – A broad Brush. Traditional Methods Cartoons, stop motion Keyframing Digital inbetweens Motion Capture What you record is what you get Simulation Animate what you can model (with equations). What is Motion Capture ?. Capture of motion of (human) actor

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Motion Capture

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  1. Motion Capture

  2. Animation – A broad Brush • Traditional Methods • Cartoons, stop motion • Keyframing • Digital inbetweens • Motion Capture • What you record is what you get • Simulation • Animate what you can model (with equations)

  3. What is Motion Capture ? • Capture of motion of (human) actor • Motion Capture of an object involves sensing, digitizing, and recording that object in motion • Whole body • Hands • Face • One way of acting out an animation

  4. Why Motion Capture ? • All the fine details of human motion will be reproduced • Naturalness of human motion is in its subtle details • Style • Mood • Weight shift, and so on • Applications • Animation / Interactive characters • Feature films / video games • Medicine • Sports • Robotics

  5. What is captured ? • What we need is • Position and orientation of the root segment • X,Y,Z , Roll, pitch, yaw • Joint angles • Length of each link • Skeleton connectivity • Skin deformation • The mocap system actually provides • Marker positions on the skin, or • The positions and orientations of markers

  6. Motion Capture Pipeline • Record motion from physical object • Use motion to animate virtual object Set up Equipment Record Motion Process Data Generate Animation

  7. What Types of Objects? • Human whole body • Portions of body • Facial animation • Animals • Puppets • Other objects

  8. How to use the data? • Off-line • Processing by filtering, inverse kinematics • Produce libraries of motion trajectories • Choose among them • Blend between them • Modify on the fly • On-line (performance animation) • Driving character directly based on what actor does in real time

  9. Motion Capture Technologies • Optical passive • Optical active • Electromagnetic • Electromechanical • Acoustic • Optical fiber

  10. Optical Passive • High resolution, high speed cameras • 120-1000 Hz, 1000x1000 pixels • Infrared or visible light strobe • Retro-reflective markers • Pros • High quality • Flexible marker placement • No cables • Not seriously constrained by markers • Cons • Extensive post-processing • Controlled environments (Indoor only, no sunlight) • Correspondence problem • Occlusion

  11. Optical Active • Phoenix Tech, ReActor, Optitrak, Visualeyez • Markers emit electric signal (LEDs) • Active output of the LED • No correspondence problem • Outdoor capture • 1/3 the cost of passive systems

  12. Optical Fiber • Bending the fiber attenuates the transmitted light • Recently used for full-body capture • Fiber Optic Sensors • Flexible FO sensors strapped to various parts of the performers body. • Sensors can directly measure joint rotations • Used in conjunction with electromagentic sensor for head and torso. • Shapewrap II • Measurand

  13. Electromagnetic • Electromagnetic field transmitter • Sensors on the body • Both position and orientation information • Pros • Realtime • No occlusion/correspondence • Cons • Limited accuracy • Smaller workspace • Heavier sensors and wires on body • Sensitive to electromagnetic interference • Company: Ascension, Polhemus

  14. Electromechanical • Exoskeleton • Mechanical skeleton attached on body • Pros • Truly realtime (500 Hz) • No range limit • No occlusion/correspondence problem • Cons • Restriction of movement • Fixed sensor positions • Company: Sacros, Gypsy

  15. Acoustic • The multiple transmitters trigger “click” • The receivers on the body measures the time taken for the sound travel • Pros • No occlusion • Cons • Limited range • Limited number of sensors • Cables on body • Acoustic interference

  16. Gollum

  17. The Polar Express

  18. Happy Feet

  19. Monster House

  20. Demos • Avatar: Motion Capture Mirrors Emotions • Devil May Cry 3 Motion Capture Video • God of War 3 Bonus Features - Motion Capture • MoCap at EA Sports • Siggraph 2011 Motion Capture Breakdown • Kinect Motion Capture - Under The HUD • iPi Desktop Motion Capture with 2 Kinect

  21. Demo 2 • motion capture technologies • Vicon (passive optical) • http://www.vicon.com/spots/vicongallery.html • PTI (active optical) • Ascension technolgy (magnetic) • MetaMotion (mechanical) • OrganicMotion (markerless) • Image Metrics (markerless -facial) • Xsens (inertial) • Mova (make-up)

  22. Motion Capture Systems • Challenges: • Signal is not perfect • Noisy • missing data • not perfectly aligned with joints • Retargeting • Data is only valid for virtual character who possesses same scale as real character.

  23. Motion Capture Systems • Challenges: • Even if motion capture data was perfect, we still have the following challenges: • Re-use – use the motion for a slightly different purpose • Creating impossible motion – Motion capture won’t do it, but may be desired in animation • Change of intent – we can’t always predict what motion we will need

  24. Motion Capture Data • So what CAN we do with motion capture data? • We can • speed up • slow down • time warp • Motion warp • However, one must remember that Captured data is Sampled Data.

  25. Retargeting Motion Capture Data • In general, moCap data is useful for a single articulated figure. • Adapt motion to another character

  26. Motion capture data formats • No “standard” moCap data format • Defacto standards from motion capture system manufacturers • Must specify both structure of skeleton as well as sampled data for each joint.

  27. Motion capture data formats • Popular formats • Acclaim File Format • .asf (Acclaim skeleton format) • .amc (Acclaim motion capture) • Biovision • .bva (BioVision animation) • .bvh (BioVision Hierarchical) • C3D • Independent Binary format with programmer support. • http://www.c3d.org

  28. Acclaim • The Acclaim format is made up of two files • a skeleton file • the ASF file (Acclaim Skeleton File). • A motion file • the AMC file (Acclaim Motion Capture data).

  29. Acclaim Skeleton File • Parsing the ASF File • “:version” • the version of the skeleton definition • ":name" • the skeleton to be named • ":units" • defines the units to be used for various types of data • Ex) mass, length, angle • ":documentation" • ":root" • the root segment of the skeleton hierarchy • "axis" : defines the rotation order of the root object • "order" : order they will appear in the AMC file • TX TY TZ RZ RX RY  Translation & Rotation Order • "position" and "orientation" • the starting position and orientation of the root • These are typically, but not always, zero

  30. Acclaim Skeleton File • Parsing the ASF File • “:bonedata” • a description of each of the segments • "begin" and "end" pair • “id” : a unique id for the segment • "name" : the name of the segment • "direction" • defines the direction from the parent to the child segment • "length" : The length of the segment • "axis" : an axis of rotation for the segment • "dof" : specifies the number of motion channels • "limits" : limits on each of the channels in the dof specification

  31. :hierarchy begin root hips hips hips1 hips2 hips3 hips1 chest chest chest1 chest2 chest3 chest1 neck neck head chest2 leftcollar leftcollar leftuparm leftuparm leftlowarm leftlowarm lefthand chest3 rightcollar rightcollar rightuparm rightuparm rightlowarm rightlowarm righthand hips2 leftupleg leftupleg leftlowleg leftlowleg leftfoot hips3 rightupleg rightupleg rightlowleg rightlowleg rightfoot end Acclaim Skeleton File • Parsing the ASF File • “:hierarchy” • Describes the hierarchy of the bones declared in the “:bonedata” section

  32. Acclaim Motion Capture Data • Parsing the AMC file • defines the actual channel animation • a line declaring the frame number • the bone animation data • bone name and data for each channel defined for that bone. • Tool • ASF/AMC Viewer

  33. Biovision BVH • BVH(BioVision Hierarchical data ) • developed by Biovision, a motion capture services company • A BVH file has two parts • a header section • describes the hierarchy and initial pose of the skeleton • a data section • contains the motion data

  34. Biovision BVH • Header section • "HIERARCHY“ • "ROOT" • followed by the name of the root • "{ " and " } " pair • "OFFSET" • X,Y and Z offset of the segment from its parent • "CHANNELS" • the number of channels • the type of each channel • "JOINT" • identical to the root definition except for the number of channels • "OFFSET " , "CHANNELS" • "End Site" • indicates that the current segment is an end effector (no children) • "OFFSET " - 6 channels for the root (Tx Ty Tz Rz Rx Ry) - 3 channels for every other object (Rz Rx Ry)

  35. Biovision BVH • Motion Section • "MOTION" • followed by a line indicating the number of frames • "Frames:" • the number of frames • "Frame Time:" • the sampling rate of the data • Ex) 0.033333  30 frames a second • The rest of the file contains the actual motion data • The numbers appear in the order of the channel specifications as the skeleton hierarchy was parsed

  36. Biovision BVH • Interpreting the data • To calculate the position of a segment • Translation information • For any joint segment • the translation information will simply be the offset as defined in the hierarchy section • For the root object • The translation data will be the sum of the offset data and the translation data from the motion section • Rotation information • comes from the motion section http://accad.osu.edu/research/mocap/mocap_data.htm#

  37. Motion Tools • Tools • Bvhacker: http://davedub.co.uk/bvhacker/ • Qavimator: http://www.qavimator.org/ • Motion Capture Display and Editing: • ASF/AMC viewer

  38. Examples • Avimator 1. The File Menu File management, Program options, and Settings. 2. Figure: The Posing / Animation dummy (or Actor), standing on the stage: This is our main click and drag edit element. 3. Frame Slider Bar: the control to move between frames. 4. Edit Part Menu: An alternative to click select. A Menu to pick a particular body part to be edited. 5. Rotational Sliders: Fine controls to edit the X,Y,Z coordinates of selected body part. 6. Play Button / Keyframe Button: Preview plays animation / Sets the “Keyframe” of an animation. 7. Frame Quantity edit box: This is the control to edit the number of frames in an animation.

  39. Examples : Avimator • Step 1 • Open “Relaxed.bvh” • Change the number of frames to “90” • Step2 • choosing male or female and turning off the joint limits. • Step3 • Keyframe Animation • in between frames (=Keyframe) • Step4 • Move to frame “2” and click the “key frame” button. • Setup our Actor to the starting position of the salute. 1. Shift Double-Click rShldr X=-4 Y=-4 Z=82 2. Shift Double-Click rForeArm X=16 Y=9 Z=0 3. Shift Double-Click rThigh X=0 Y=1 Z=0 4. Shift Double-Click rShin X=1 Y=1 Z=0 5. Shift Double-Click rFoot X=0 Y=-3 Z=-4

  40. Examples : Avimator • Step 5 • Move to frame “30”. 1. Select rCollar X=0 Y=-52 Z=-23 2. Select rShldr X=23 Y=106 Z=82 3. Select rForeArm X=-12 Y=99 Z=-9 • Step 6 • Frame “30”  COPY FRAME. • move to frame “80”  PASTE FRAME • click the “Key Frame” button • Step 7 • Frame “2”  COPY FRAME. • move to frame “90”  PASTE FRAME • click the “Key Frame” button • Step 8 • play our animation • our actor (or actress) should be repeatedly saluting us. • Step 9 • save our file as before with FILE and SAVE. “salute_anim.bvh”

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