Animating Sand, Mud, and Snow

Abstract

Computer animations often lack the subtle environmental changes that should occur due to the actions of the characters. Squealing car tires usually leave no skid marks, airplanes rarely leave jet trails in the sky, and most runners leave no footprints. In this paper, we describe a simulation model of ground surfaces that can be deformed by the impact of rigid body models of animated characters. To demonstrate the algorithms, we show footprints made by a simulated runner in sand, mud, and snow as well as bicycle tire tracks, a bicycle crash, and a falling runner. The shapes of the footprints in the three surfaces are quite different, but the effects were controlled through six essentially orthogonal parameters. To assess the realism of the resulting motion, we compare the simulated footprints to video footage of human footprints in sand.