QOTA: a fast, multi-purpose algorithm for terrain following in virtual environments

To keep avatars and other moving objects on the ground in virtual environments, it is necessary to find the points where these objects should contact the terrain. This is often done using collision detection; however, this is inefficient, because general collision detection solves a problem that is inherently more complex than merely determining terrain contact points. Because the Quick Oriented Terrain Algorithm (QOTA) focuses solely on the problem of intersecting lines of a predetermined orientation with a terrain model, it provides very rapid support for terrain following. For example, given a 13,000 polygon terrain, QOTA running on a 250MHz R4400 MIPS processor can calculate an intersection point in less than 19 microseconds (1.9 x 10 -5 seconds). Given a preferred orientation, such as the direction of the gravity vector, for the lines to be intersected with a terrain, QOTA uses a pre-processing step that sorts the terrain polygons into a quadtree and adds bounding boxes and polygon edge equation parameters to speed up polygon containment checking. In the example above, this preprocessing takes approximately 2 seconds. In addition to terrain following, QOTA is useful for detecting certain limited kinds of collision detection and determining containment. This work may not be copied or reproduced in whole or in part for any commercial purpose. Permission to copy in whole or in part without payment of fee is granted for nonprofit educational and research purposes provided that all such whole or partial copies include the following: a notice that such copying is by permission of Mitsubishi Electric Research Laboratories of Cambridge, Massachusetts; an acknowledgment of the authors and individual contributions to the work; and all applicable portions o f the copyright notice. Copying, reproduction, or republishing for any other purpose shall require a license with payment of fee to Mitsubishi Electric Research Laboratories. All rights reserved. Copyright © MERL A Mitsubishi Electric Research Laboratory , 1996 201 Broadway, Cambridge, Massachusetts 02139