Transcript Motion Capture Laboratory

Motion Capture
Laboratory
School of Arts and Humanities
Erik Jonsson School of Engineering and
Computer Science
University of Texas at Dallas
What is Mocap?
• The creation of a 3D
representation of a live
performance.
Understanding Motion Capture for Computer Animation and Video Games by Alberto
Menache.
Applications
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Entertainment
Medicine
Arts / Education
Science / Engineering
Entertainment: Live Action Films
• Computer generated characters in live action
films (e.g. Battle Droids and many others in
Star Wars Prequels, Gullum in The Lord of
the Rings, King Kong in King Kong)
Entertainment: 3D computer
animations
• Characters in computer animated files (e.g.
Polar Express, Monster House)
Entertainment: Video Games
• Video games by Electronic Arts,
Gremlin, id, RARE, Square, Konami,
Namco, and others, (e.g. Enemy
Territory)
Medicine
• Medicine (e.g., gait analysis, rehabilitation)
• Sports medicine (e.g. injury prevention,
performance analyses, performance
enhancement)
Gait Analysis Service
Arts / Education
• Dance and theatrical performances
• Archiving (e.g., Marcel Marceau)
OSU/ACCAD
Science / Engineering
• Computer Science (e.g., human motion
database, indexing, recognitions)
• Engineering (e.g., Biped robot developments)
• Ergonomic product design
• Military (e.g., field exercises, virtual
instructors, and role-playing games)
Mocap animation
• Motion capture animation is different
from keyframe animation in terms of
how motion is created.
• Same principles apply to mocap
animation & keyframe animation!
• A combination of motion capture
animation and keyframe animation is
often used.
Keyframe animation
• A keyframe is a drawing of a key moment in
an animated sequence, where the motion is
at its extreme.
• Inbetweens fill the gaps between keyframes.
• Every motion is created by animators.
Advantages of mocap animation
• Faster to create (only if an established
production pipeline exists.)
• Secondary motions and all the subtle
motions are captured -> more realism.
• Physical interactions between
performers and props can be captured.
Disadvantages of mocap
animation
• Cost.
• Manipulating mocap data is often
difficult -> Re-capturing or key framing a
shot with bad data is often easier.
• Mapping mocap data of a performer to a
character with a different proportion
often causes problems.
Types of mocap equipment
• Magnetic systems
• Mechanical systems
• Optical systems
Magnetic systems
• Utilize sensors placed on the body
to measure the magnetic field
generated by a transmitter source.
Magnetic systems
•  Require no special lighting
condition.
•  Sensors are never occluded.
• X Require a metal-fee environment.
Mechanical systems
• Exoskeleton with angle sensors.
Mechanical systems
•  Measure joint angles (no marker ID
problems).
•  Sensors are never occluded.
• X Breakable!
• X Configuration of sensors is fixed.
• X Constrains on joints.
Optical systems
• The cameras are equipped with infrared
LED's and filters. (Filters enhance the
contrast of the image.)
• The cameras see reflector markers.
Optical systems
•  Higher sampling rate.
•  Larger capture space.
• X Markers are sometimes occluded ->
marker ID problems.
• X Provide only positional data -> joint
angles need to be computed.
Mocap system at UTD
• Vicon optical system - Best system in
Academia!
• 8 high-speed MX 13 (up to 1000 fps)
and 8 high-resolution MX 40 (4 million
pixels) cameras.
• Capture up to 5 performers at once.
Mocap system at UTD
• Vicon optical system - Best system in
Academia!
• 8 high-speed MX 13 (up to 1000 fps)
and 8 high-resolution MX 40 (4 million
pixels) cameras.
• Capture up to 5 performers at once.
Production pipeline overview
• Calibrate the system.
• Fit a generic skeleton to the subject’s proportion
(subject calibration).
• Capture shots & reconstruct 3D trajectories using the
calibrated subject.
• Link the subject specific skeleton to a CG character’s
skeleton and edit motion (in MotionBuilder).
• Add skin to the CG character, edit motion, and render
(in Maya).
Pipeline flow chart & Detailed pipeline