what is motion capture? - duke computer sciencemechanical motion capture high accuracy high data...
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What is Motion Capture?capture of motion of (human) actor
whole bodyupper bodyface
more generally...one way of using a physical device to control animation
puppeteeringexoskeletonsdiscrete sensors on actors
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Applicationsmoviestv showsvideo gamesperformance animation
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Motion CaptureWhat do we need to know?
Errors cause
x, y, zpitch, roll, yaw
Sampling Rate and Accuracy
joints to come apartlinks to grow/shrinkbad contact points
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How to use the data?off−line
choose among themswitch between themmodify
on−line
libraries of motion trajectoriesfiltering, IK
driving character directly basedon what actor does in real time
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Historyrecording motion for biomechanics
high accuracyfewer recorded pointshand digitizing filmsupplement with force plate, foot switches
robot measurementsSelspot LED system
VR tracking technologyless accuracyfewer sensors
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Technology−−optical
hand or semi−automatically digitizedtime consuming
no glossy or reflective materialstight clothingocclusion of markers by props or limbshigher frames/second
passive reflection−−Peak
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Technology−−optical
automatically digitized240 Hznot real−time3 markers/body part for 6 dof2+ cameras for 3d position data~$100K
passive reflection−−Acclaim, Motion Analysis,...
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Technology−−optical
automatically digitizedcorrespondence256 markers3,500 markers/second
active light sources −− Optotrak
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Technology−−magneticelectromechanical transducers
Ascension flock of birdsPolhemus Fastrak
limited range/resolutionpigtail (new wireless system)metal in the environment
(treadmill, rebar!)no identification problem6 dof informationrealtimelow frequency: 30 to 120 Hzfew markers: 10−20$40K
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Technology−−mechanicalmechanical motion capture
high accuracyhigh data ratenot realistic motionhire animator
monkeydataglovelow accuracyfocused resolutionrecognize gestures
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Technology−−mechanicalexoskeleton + angle sensors
Analogous
pigtail no identification problemrealtimehigh frequency: 500Hznot range limitedfitrigid body approximation
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Technology Issues:resolution/range of motioncalibration
occlusion/correspondence
accuracymarker movement/placementsensor noise
skew in measurement timerestrictions on the environment
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Technology Issues:resolution/range of motion
calibration
occlusion/correspondence
accuracymarker movementsensor noise
skew in measurement timerestrictions on the environmentframe rate
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Resolutionpositioning of camera
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Calibrationinternal camera parameters
external parameters
correlation between multiple cameras
position and orientation
optical distortion of lens
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Marker Placementlocation should move rigidly with jointstay away from bulging musclesshoulders: skeletal motion not closely tiedto motion on skin
Calibrationzero positionfine calibration by hand
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Accuracymarker movementsensor noiseskew in measurement time
filtering (requires high data rate)
time
position
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Model−based Techniques
objects don’t pass through each other
restricted search space for markers
no infinite accelerations model of bodies for occlusion