Motion Capture Laboratory School of Arts and Humanities

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 3 D representation of a live performance. Understanding Motion Capture for Computer Animation and Video Games by Alberto Menache.

Applications • • 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: 3 D 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.

Production pipeline overview • Calibrate the system. • Fit a generic skeleton to the subject’s proportion (subject calibration). • Capture shots & reconstruct 3 D trajectories using the calibrated subject. • Link the subject specific skeleton to a CG character’s skeleton and edit motion (in Motion. Builder). • Add skin to the CG character, edit motion, and render (in Maya). Pipeline flow chart & Detailed pipeline