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

Applicationsmoviestv showsvideo gamesperformance animation

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

Resolutionpositioning of camera

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

Model−based Techniques

objects don’t pass through each other

restricted search space for markers

no infinite accelerations model of bodies for occlusion