Motion Capture Laboratory

School of Arts and HumanitiesErik 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

• 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