A procedural approach to animate interactive natural sceneries

This paper presents a method for animating and rendering an interactive natural scenery in real-time. It improves the prairie model of [I I I] by enabling the on-the-fly generation of blades of grass, at three different levels of detail, from user-specified density maps. A new animation function, the tread on grass, is defined to allow virtual objects or characters to crush the grass. The resulting grass model is incorporated into a more complex natural scene with the adjunction of trees that respond to the same wind. Results are illustrated by the real-time animation of autonomous virtual humans interacting with this natural scenery.

1. Introduction

Real-time applications such as driving simulators or video-games are more and more demanding complex outdoors scenes: an uneven terrain with animated grass, trees, rivers or water-falls, a sky with dancing clouds will be much more appealing than a conventional static environment. To feel really immerged, the user should not only be able to visit this animated scenery, but also to interact with it through the vehicle or the avatar he is controlling. This consists in both feeling the effect of the local slope and vegetation onto the avatar's motion and seeing the immediate consequences of this motion on the scenery, such as foot-prints or grass trodden down.