Plausible Motion Simulation
for Computer Graphics Animation

Abstract:

Accuracy is the ubiquitous goal of dynamic simulation, in order to yield the ``correct'' motion. But for creating animation, what is really of interest is ``plausible'' motion, which is somewhat different. We discuss what we mean by plausible simulation, how it differs from ``accurate'' simulation, and why we think it's a worthwhile area to study. The discussion touches on questions of physically plausible vs. visually plausible motion, plausible simulation in a noisy or textured environment, and probability measures for motion, as well as issues for forward and inverse problems.

Animations:

• A ball bouncing in a box, side view. A small random variation to the collision normals provides "texture" to an otherwise overly-regular animtion.



Dropped from rest:

• ``Accurate'' simulation: no variation. Bounces up and down in place. (MPEG, 245K)
• Normals varied up to 5 degrees (MPEG, 294K)
• Normals varied up to 10 degrees (MPEG, 400K)

Moving horizontally:

• ``Accurate'' simulation: no variation. (MPEG, 356K)
• Normals varied up to 4 degrees (MPEG, 452K)
• Normals varied up to 8 degrees (MPEG, 148K)
• A 9-ball pool break. A small random variation can be added to the collision normals without harming the visual plausibility of the motion.



• ``Accurate'' simulation: no variation (MPEG, 248k)
• Normals varied up to 4 degrees (MPEG, 656k)
• Normals varied up to 8 degrees (MPEG, 513k)
• 1-ball inverse problem. Given an initial position of the cue ball and a desired target position and direction, determine how to strike the cue ball to acheive the goal.



• ``Accurate'' simulation has no solutions
• Normals varied up to 2 degrees finds a "5-rail" solution (MPEG, 43K)
• Normals varied up to 5 degrees finds a "4-rail" solution (MPEG, 43K)
• 2-ball inverse problem. Given an initial position of the cue ball and a target baall, strike the cue ball to sink the target in the lower-left corner pocket.



• ``Accurate'' Simulation finds two solutions (MPEG, 43K)
• Normals varied up to 10 degrees finds three additional solutions (MPEG, 43K)