Physical Touchup of Human Motions
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Summary
Many popular motion editing methods do not take physical principles into account, potentially producing physically implausible motions. We present a method for "touching up" motions to improve physical plausibility. Specifically, we first divide the motion into ground and flight stages and then enforce zero moment point constraints in the former and linear/angular momentum constraints in the latter. Unlike previous methods, we do not employ nonlinear optimization; rather, we use efficient closed form algorithms that allow a user to build a set of hierarchical displacement maps which refine user-specified degrees of freedom at different scales.
The following video clip motivates this work.
(AVI, 15 MB, 0:51)
Approach
Starting with an edited motion in need of touchup, the user divides the body into parts that do and do not move and specifies time scales over which changes are to take place. Based on this information, displacement maps are automatically generated to adjust the motion. This is akin to specifying a set of filters that are to act on the motion.
(AVI, 25 MB, 1:21)
Control
A motion that is physically plausible may not look realistic; natural human motion is a strict subset of physically plausible motion. An important feature of our work is that users can control how changes are made in order to model human behavior. Users can select which parts move, the allowable frequencies at which they move, and how much they should contribute to the overall adjustment. The following video shows the effect of varying the contribution of the upper body when correcting an out-of-balance walking motion.
(AVI, 25 MB, 1:21)
Motion stages
The following examples contain both ground contact and flight stages, where appropriate physical laws are enforced seperately.
(AVI, 12MB, 0:40)
(AVI, 12MB, 0:40)