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