Adapting Simulated Behaviors for New Characters

• Original man runner, hand-tuned and optimized. MPEG (0.7M) QT (1.4M)
• Woman and child runners obtained by automatic scaling of man runner. MPEG (0.8M) QT (2.0M)
• Imaginary runner obtained by automatic scaling of man runner. MPEG (1.6M) QT (8.0M)
• Imaginary bikers obtained by automatic scaling of man bicyclist. MPEG (0.7M) QT (0.8M)

If simulated, human-like characters are to be useful in animations and virtual environments, we must be able to create new, appealing actors easily. Appealing human motion has several components: the kinematics and dynamics of the figure must be physically correct and the control algorithms must make the figure perform in ways that appear natural and are stylistically appropriate for the setting and character.

In this work, we develop scaling laws for adapting existing control systems to new dynamic models to facilitate the rapid creation of new actors. When simulation is used for animation, adapting behaviors to new actors is difficult because a control system that is tuned for one actor will not work on an actor with different limb lengths, masses, or moments of inertia. We adapt the control system to a new actor in two stages. First, the control system parameters are scaled based on the size and moment of inertia of the dynamic models for the new and the old actors. Then a subset of the parameters is fine-tuned using a search process based on simulated annealing. Projects to date have included animating the running motion of a woman, child, and imaginary character by modifying the control system for a running man, and animating the bicycling motion of an imaginary character by modifying the control system for a bicycling man. We evaluate the results of this approach by comparing the motion of the simulated child and woman with that of actual humans and data published in the literature.

This scaling algorithm can also be used to maintain physical realism during an on-line metamorphosis from one character to another. A special effect can be created where one character is gradually morphed to a second character while smoothly performing a dynamic behavior. Using this technique, we have animated a continuous metamorphosis of a running man to a running woman.

Publications

• Hodgins, J. K. and Pollard, N. S., 1997. Adapting Simulated Behaviors For New Characters, SIGGRAPH 97 Proceedings, Los Angeles, CA. (Acrobat format)

Project Members

Jessica K. Hodgins
jkh@cc.gatech.edu
Nancy S. Pollard
nsp@cc.gatech.edu

Copyright 1997

Questions or comments? Email jkh@cc.gatech.edu.