Specifying Stochastic Objects in a Hierarchical Graphics System

Many graphics systems allow a user to describe three dimensional objects with polygon meshes or surface patches. However to achieve realistic scenes for making animated film some objects are better described with stochastic techniques. Some examples would be clouds. tire and mountains. We describe here a hierarchical graphics system consisting of objects which contain geometrical transformations of other objects or primitives. Each object is treated in a consistent fashion whatever the types of primitives that are ultimately called. for example an object may consist of polygon mesh sub-objects and stochastic objects. The system has been designed so that it may easily be extended to include new primitive types. so far a subsystem for generating particles (fire. volcanos etc.) and a sub-system for generating fractal polygons have been implemented Examples are given of the results obtained with this technique.