[SOLVED] CS chain database Motion Capture Technologies

Motion Capture Technologies
Jessica Hodgins

Animation
Video Games Robot Control
Motion Capture

What games use motion capture?
NBA live
PGA tour
NHL hockey
Legends of Wrestling 2
Lords of Everquest
Lord of the Rings
Tony Hawk Pro Skater
Batman: Dark Tomorrow
Grand Theft Auto
Soul Caliber

Motion Capture
Track motion of reference points
Convert to joint angles
Use angles to drive an articulated model
Motion paths can then be combined to give greater control

What is Captured?
What do we need to know?
X,Y,Z
Roll, pitch, yaw
Errors cause
Joints to come apart Links to grow/shrink Bad contact points

Off-line
How to use the data
Processing by filter, inverse kinematics
Produce libraries of motion Choose among them
Blend between them
Modify on the fly
On-line (performance animation)
Driving character directly based on what user does in real-time. Konami games (for a few dof)

Production Pipeline

What is captured?
Dynamic motions?
House of Moves

Scale?
What is captured?
Motion Analysis

What is captured?
Non-rigid objects?
House of Moves

What is captured?
Props often cause problems
Ball in pingpong Fly fishing
Sword
Passive behaviors are hard
Complicated motion of clothing Explosions

Calibration
Technology Issues
Resolution/range of motion
Accuracy
Marker movement Capture rate
Occlusion/correspondence

Marker Placement
Location should move rigidly with limb
Stay away from bulging muscles
Shoulders: skeletal motion not closely tied to skin
Shoulders: not a rigid body chain

Marker Set
3Dpoints->jointangles
Itmatters!
Sodoassumptionsabouthumankinematics

Calibration of cameras
Calibration
Fairly automatic with L-bracket and wand
Calibration of subject
Also fairly automatic but not so accurate What are limb lengths
What are joint limits?
Where are markers wrt to joints?

Eric Darnell, co-director of Antz
The main problem with motion capture associated with characters has to do with mass distribution, weight, and exaggeration. He says that it is impossible for a performer to produce the kind of motion exaggeration that a cartoon character needs, and the mass and weight of the performer almost never looks good when applied to a character of different proportions.

Richard Chuang, VP at PDI
The mapping of human motion to a character with non-human proportions doesnt work, because the most important things you get out motion capture are the weight shifts and the subtleties and that balancing act of the human body. If the proportions change, you throw all that out the door, so you might as well animate it.

Godzilla: Karen Goulekas
The reason that we pulled the plug on using the motion capture was, very simply, because the motion we captured from the human actor could not give us the lizard-like motion we were seeking. The mocap could also not reflect the huge mass of Godzilla either. During our keyframe tests, we found that the Godzilla motion we wanted was one that maintained the sense of huge mass and weight while still moving in a graceful and agile manner. No human actor could give us this result.

Retargeting
Research Topics
Marker placement/extraction of skeleton
Capture of deforming skin rather than pretending it is a rigid chain?
Constraint satisfaction
Generalization of data Interpolation
Interfaces for controlling human motion

Motion Database

User Specified Path
Jehee Lee, Jinxiang Chai, Paul Reitsma, Jessica Hodgins, Nancy Pollard SIGGRAPH 2002

Find Transitions and Re-sequence
Motion Capture Region Virtual Environment
Sketched path
Obstacles

Find Transitions and Re-sequence
Motion Capture Region Virtual Environment

Unstructured Input Data

Connecting Transitions

Synthetic Transitions
Good transitions taken with high probability
Video Texture [Schoedl et al. SIGGRAPH 2000]
Poses
Velocities
Contact state

Search to Find Path

Motion Data for Rough Terrain

Motion Data for Rough Terrain

Comparison to Real Motion

Comparison to Real Motion

What are the tricks?
Enough data?
Wash out yaw
Only locomotion
Wash out yaw?

Why isnt this used in industry?
No control over transitions?
More dynamic behaviors so automatic transitions would be few?
Havetoplanforshootanywaysomightas well plan for transitions?
Notenoughdata?

Next lecture
Details on transition metrics
Details on washing out yaw
Representations for orientation Euler angles
Quaternions Axis/angle
A bit about editing, generalizing