Motion Capture Animation

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Motion Capture Animation

• Dr. Midori Kitagawa
• Arts and Technology Program
• University of Texas at Dallas

Gif animations by Dax Norman
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What is Mocap?

• Motion capture (mocap) is sampling and recording
  motion of humans, animals, and inanimate objects
  as 3D data.
• The data can be used to study motion or to give
  an illusion of life to 3D computer models.

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Applications

• Entertainment
• Medicine / Sports
• Arts / Education
• Science / Engineering

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Entertainment Live Action Films

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Entertainment 3D computer animations
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Entertainment Video Games
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Medicine / Sports

• Medicine (e.g., gait analysis, rehabilitation)
• Sports (e.g. injury prevention, performance
  analyses, performance enhancement)

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Arts / Education

• Dance and theatrical performances
• Archiving (e.g., Marcel Marceau)

OSU/ACCAD
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Science / Engineering

• Engineering (e.g., biped robot developments)
• Computer Science (e.g., human motion database,
  indexing, recognitions)
• Design (e.g., ergonomic product design)
• Military (e.g., field exercises, virtual
  instructors, and role-playing games)

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Mocap animation

• Motion capture animation is different from
  keyframe animation in terms of how motion is
  created.
• Same principles of animations apply to mocap
  animation keyframe animation!
• Combination of motion capture animation and
  keyframe animation is often used.

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Keyframe animation

• 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.

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Advantages of mocap animation

• Faster to create (only if an established
  production pipeline exists.)
• Secondary motions and all the subtle motions are
  captured.
• -gt more realism
• Physical interactions between performers and
  props can be captured.
• -gt more realism

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Disadvantages of mocap animation

• Cost.
• Manipulating mocap data is often difficult -gt
  Re-capturing or key framing a shot with bad data
  is often easier.
• Mapping mocap data of a performer to a 3D
  character with a different proportion may cause
  issues.

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Popular types of mocap equipment

• Optical systems
• Magnetic systems
• Mechanical systems
• Inertial systems
• Vision based systems

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Optical systems

• The cameras are equipped with infrared LED's and
  filters.
• The cameras see reflector markers.

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Optical systems

• ? Higher sampling rate.
• ? Larger capture space.
• ? Marker configuration is flexible.
• X Markers are sometimes occluded -gt marker ID
  problems.
• X Provide only positional data -gt joint angles
  need to be computed.

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Magnetic systems

• Utilize sensors placed on the body to measure the
  magnetic field generated by a transmitter source.

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Magnetic systems

• ? Require no special lighting condition.
• ? Sensors are never occluded.
• X Affected by electromagnetic force.
• X Low sampling rate.
• X Multiple capture subjects can cause
  interferences when they get close to each other.

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Mechanical systems

• Exoskeleton with angle sensors.

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Mechanical systems

• ? Measure joint angles -gt no marker ID problems.
• ? Sensors are never occluded.
• ? Require no special lighting condition.
• X Breakable!
• X Configuration of sensors is fixed.
• X Constrains on joints.
• X Translation is computed -gt can cause drifting.

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Inertial systems

• Inertial measurement units (IMUs) containing a
  combination of gyroscope, magnetometer, and
  accelerometer, to measure rotational rates.
• The motion data of the inertial sensors is
  transmitted wirelessly to a computer, where the
  motion is recorded or viewed.

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Inertial systems

• ? Sensors are never occluded.
• ? Require no special lighting condition.
• ? Can be used underwater.
• ? Configuration of sensors is flexible.
• X Translation is computed -gt cause drifting.
• X Sampling rate is low.

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Vision-based systems

• Computer vision based algorithms analyze streams
  of video input, identify human forms, and track
  human movements.
• ? Requires no markers or sensors.
• ? No device is attached to a capture subject. No
  constrain on a capture subject.
• X Do not recognize some gestures.

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Mocap system at UTD

• Vicon optical system
• 8 high-speed MX 13 (up to 10,000 fps) and 8
  high-resolution MX 40 (4 megapixels) cameras.
• Capture up to 5 performers at once.

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Mocap animation pipeline

• Preproduction

Capture -gt data cleaning -gt retargeting Modeling
-gt rigging -----------------------------
mocap animation Keyframe animation Effect
animation Sound design Texturing/lighting -gt
Rendering -gt Composition

• Post-production