Motion Capture
Animation
Dr. Midori Kitagawa
Arts and Technology Program
University of Texas at Dallas
Gif animations by Dax Norman
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.
Applications
•
•
•
•
Entertainment
Medicine / Sports
Arts / Education
Science / Engineering
Entertainment: Live Action Films
Entertainment: 3D computer
animations
Entertainment: Video Games
Medicine / Sports
• Medicine (e.g., gait analysis, rehabilitation)
• Sports (e.g. injury prevention, performance
analyses, performance enhancement)
Arts / Education
• Dance and theatrical performances
• Archiving (e.g., Marcel Marceau)
OSU/ACCAD
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 roleplaying games)
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.
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.
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.
-> more realism
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 3D character with a
different proportion may cause issues.
Popular 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 Affected by electromagnetic force.
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.
• 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
• 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.
Mocap animation courses
Graduate level: ATEC 6352 & UG level: ATEC 4345
• Group project based
• Group of 3 to 5 members
• Semester long project
Pre-requisite:
• ATEC 3317 Modeling and texturing
OR
• ATEC 3327 Lighting and composition
Recommended:
• ATEC 3328 Rigging I
• ATEC 4337 Computer Animation
Mocap animation pipeline
Preproduction
Capture -> data cleaning -> retargeting
Modeling -> rigging ----------------------------- mocap animation
Keyframe animation
Effect animation
Sound design
Texturing/lighting -> Rendering -> Composition
Post-production
* Tasks that everyone should be involved.
* Tasks that can be designated to a member or members.
System Calibration and Capturing and Processing Data
2D Image -> 2D Camera Data -> 3D Markers Positions -> Trajectories -> Recon Skeleton -> Solver Skeleton
Reconstruction
Triangulation
Circle fitting
FBX
Skeleton with subject’s
size & proportion and
motion data
BLADE
Subject Calibration
VST
• Capture Range of
(subject
Motion (ROM)
template)
• Reconstruct trajectories
of ROM
• Label markers
VSK
Skeleton with subject’s
size & proportion
Mocap Pipeline
Flow Chart
The processes that you
go through for each
character
MOTION
BUILDER
Character Setup
• Correlate :
Character
&
Character Setup
FBX
• Create a skeleton
The processes that
you repeat for each
shot
MAYA
Rendering
MB
Maya Scene File
(FBX)
• Edit motion
Skeleton with 3D character’s
size & proportion (and skin)
• Bind skin to the skeleton
• Rig the character
Character
• Marge the rigged character (MB) and
the skeleton with motion data (FBX)
• Edit motion (IK/FK blend, Trax)
• Render
• Bake motion data to the
skeleton
FBX
Skeleton with motion data & 3D
character’s size & proportion
Dr. Midori Kitagawa
midori@utdallas.edu
ATEC 1.909