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
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
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
Historyrecording motion for biomechanics
high accuracyfewer recorded pointshand digitizing filmsupplement with force plate, foot switches
robot measurementsSelspot LED system
VR tracking technologyless accuracyfewer sensors
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
Technology−−optical
automatically digitized240 Hznot real−time3 markers/body part for 6 dof2+ cameras for 3d position data~$100K
passive reflection−−Acclaim, Motion Analysis,...
Technology−−optical
automatically digitizedcorrespondence256 markers3,500 markers/second
active light sources −− Optotrak
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
Technology−−mechanicalmechanical motion capture
high accuracyhigh data ratenot realistic motionhire animator
monkeydataglovelow accuracyfocused resolutionrecognize gestures
Technology−−mechanicalexoskeleton + angle sensors
Analogous
pigtail no identification problemrealtimehigh frequency: 500Hznot range limitedfitrigid body approximation
Technology Issues:resolution/range of motioncalibration
occlusion/correspondence
accuracymarker movement/placementsensor noise
skew in measurement timerestrictions on the environment
Technology Issues:resolution/range of motion
calibration
occlusion/correspondence
accuracymarker movementsensor noise
skew in measurement timerestrictions on the environmentframe rate
Calibrationinternal camera parameters
external parameters
correlation between multiple cameras
position and orientation
optical distortion of lens
Marker Placementlocation should move rigidly with jointstay away from bulging musclesshoulders: skeletal motion not closely tiedto motion on skin
Calibrationzero positionfine calibration by hand
Accuracymarker movementsensor noiseskew in measurement time
filtering (requires high data rate)
time
position