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Notes

Notes. Example final exam up in Work section of website Take with a grain of salt Collision notes part 1 (primitive operations) up in Resources section Review session coming up on Friday Final projects: if you need to do a demo Email me your code by the deadline

teagan-rich
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Notes

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  1. Notes • Example final exam up in Work section of website • Take with a grain of salt • Collision notes part 1 (primitive operations) up in Resources section • Review session coming up on Friday • Final projects: if you need to do a demo • Email me your code by the deadline • Also email me to set up a time for demo, either after class or the following Monday/Tuesday cs426-winter-2008

  2. Motion Capture • A lot of human motion is very subtle, and hard to nail down with the usual tools • E.g. shifting balance, complex joints, personality… • Motion capture (mocap) instead records real motion from actors • E.g. Gollum, Polar Express, Beowulf, a lot of TV shows, plenty of games • Technical difficulties: • How do you record? • What do you do with the data? cs426-winter-2008

  3. Mocap methods • Most common: “marker-based” • E.g. draw dots on the actor’s face, or dress in black and attach retro-reflective balls in key places • Film from one or more cameras (preferably calibrated and synchronized, preferably with a strobe light) • Reconstruct 3D positions of markers in each frame through inverse solve • Some “markerless” systems: rely on good computer vision algorithms • Some use direct or electromagnetic measurement cs426-winter-2008

  4. Skeleton modeling • Most systems only can measure path of points on skin/clothing • For full-body motion, usually want this instead in terms of global pose + joint angles in a skeletal model • Film actor in neutral reference pose first, set up correspondances • Another data fitting problem(and source of error) • Often allow for stretchable bones to correct joint modeling errors cs426-winter-2008

  5. Footskate • Almost inevitably stuck with one particularly bad error: “footskate” • Feet that should stay planted on the floor slide around (and up and down) • Enough to be noticeable! • Need to clean this up specially • E.g. Kovar, Gleicher & Schreiner SCA 2002 • Detect footplants • Apply IK on legs and hips to keep feet in place • Smooth over a few frames to avoid pops cs426-winter-2008

  6. What to do with the data • Simplest: play it back • If it’s not what you want, record it again? • Directly edit in animation tool • No notion of layers though; very hard to change without wiping out all the subtleties • Motion warping • Witkin & Popovic, SIGGRAPH’95 • Retime (use time as a motion curve) • Add smooth, slow components to motion curves to hit desired key frames • Hope nobody notices! cs426-winter-2008

  7. Move trees • Standard videogame solution • Design a graph corresponding to available player actions • E.g. walk forward, turn, jump, … • Design and record corresponding actions with mocap • Warp/retime/edit to make clips easily transition where needed • Note: in playback need to keep separate track of global position/orientation cs426-winter-2008

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