1cs426-winter-2008 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 me your code by the deadline Also me to set up a time for demo, either after class or the following Monday/Tuesday

2cs426-winter-2008 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?

3cs426-winter-2008 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

4cs426-winter-2008 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

5cs426-winter-2008 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

6cs426-winter-2008 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!

7cs426-winter-2008 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