What is motion capture? Motion capture A technology of recording the movement of real things -- usually humans Applications What is captured? Computer animation Biomechanics Robotics Objects Humans Cinema Video games Anthropology Animals Celebrities
What is captured? Pros and cons Truthfully record all the fine details of the natural motion The captured motion is difficult to be generalized Whole body modified Face controlled Hands How to use the data? Types of Systems Off-line Motion libraries Optical systems Motion graphs Magnetic systems Training examples Motion tapes On-line Drive characters based on the movement of the actors in real time
Optical systems Magnetic system Cumbersome sensors (heavier and also wired) Smaller workspace Cameras Record both position and orientation High temporal resolution (120+ fps) Lower resolution (80 fps max) Detect the locations of reflective markers Sensitive to EMI/metal in the environment Markers Sensitive to infrared Motion tapes Motion capture pipeline Contain optical fibers and calibration capturing sensors that can detect the model bending and twisting building Restriction of movement Another technology for detecting root translation marker labeling trajectory inverse Measure the shape of surface smoothing kinematics precisely
Motion capture pipeline Calibration calibration capturing Static calibration model building Figure out where the floor is Dynamic calibration marker Figure out the capture volume labeling trajectory inverse smoothing kinematics Motion capture pipeline Capturing Marker placement calibration capturing Markers should move rigidly model with joints building Asymmetric placement helps in post-processing T-pose and joint exercises marker labeling Recording specific poses can trajectory inverse help estimating bone lengths smoothing kinematics
3D marker position Motion capture pipeline calibration capturing In principle, two cameras are sufficient to reconstruct model the 3D location of a marker building In practice, more cameras can reduce occlusion marker increase precision labeling trajectory inverse smoothing kinematics Model building Problem statement Given recored marker positions, estimate the dimension of each body part + Optimize both bone length and handle positions at the same time Templates and heuristics help generic skeleton specific pose used bone length rough handle positions for calibration handle offset
Motion capture pipeline marker labeling calibration capturing model Ghost markers building Missing markers Switching trajectories marker labeling trajectory inverse smoothing kinematics Raw data Motion capture pipeline calibration capturing model building marker labeling trajectory inverse 3D locations of markers smoothing kinematics
Inverse kinematics Motion capture pipeline calibration capturing model building Input: articulated body with handles + desired handle marker positions labeling trajectory inverse smoothing kinematics Joint angles that move handles to desired positions Trajectory smoothing Issues The main problem with motion capture associated with characters has to do with mass distribution, weight and exaggeration. It Global optimization that minimizes the velocity of the is impossible for a performer to produce the kind of motion exaggeration that a cartoon character needs, joint angles while staying as close as possible to the and the mass and weight of the performer almost desired handle positions never looks good when applied to a character of different proportions. Eric Darnell, codirector of Antz
Issues Motion-based user interface The mapping of human motion to a character with non-human proportions doesn’t work, because the most important things you get out of motion capture are the weight shifts and the subtleties and that balancing act of the human body. If the proportions change, you throw all that out the door, so you might as well animate it. Richard Chuang, VP at PDI
Recommend
More recommend
