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Distributed virtual reality systems require accurate, efficient remote rendering of animated entities in the virtual environment. Position, velocity, and acceleration information about each player is maintained at the player's local machine, but remote hosts must display this information in real-time to support interaction between users across the network. Prior applications have transmitted position information at the local frame rate, or they have relied on dead-reckoning protocols using higher derivative information to extrapolate entity position between less frequent updates. These approaches require considerable network bandwidth and at times exhibit poor behavior. This paper describes a position history-based protocol whose update packets contain only position information. Remote hosts extrapolate from several position updates to track the location and orientation of entities between infrequent updates. Our evaluation suggests that the position history-based protocol provides a network-scalable solution for generating smooth, accurate rendering of remote entities.

Users of distributed virtual reality applications interact with users located across the network. Similarly, distributed object visualization systems store dynamic data at one host and render it in real-time at other hosts. Because data in both systems is animated and exhibits unpredictable behavior, providing up-to-date information about remote objects is expensive. Remote hosts must instead apply extrapolation between successive update packets to render the object's true animated behavior. This paper describes and analyzes a position history-based" protocol in which hosts apply several recent position updates to track the position of remote objects. The history-based approach o ers smooth, accurate visualizations of remote objects while providing a scalable solution.

Distributed interactive simulation systems are growing to include well over 100,000 dynamic entities for applications such as multiplayer video games, military and industrial training, and collaborative engineering. In these applications, each host receives updates (such as position and orientation) from remote entities, models and renders the scene, and pegorms other tasks such as collision detection. The number of entities places a heavy burden on both the networking resources and computational resources available to the application. To address these limitations, some systems have aggregated information about groups of simulation entities according to their organizational structure or their location within the virtual world. Howevel; traditional aggregation techniques are inadequate because remote hosts need to access entities based on both their organization and their virtual world position. This paper describes projection aggregations, a technique for grouping entities by both their organization and location. Remote hosts use projections to control which entities are represented locally and at what level-of-detail. We describe how projection aggregations are implemented in a networked environment and demonstrate how they reduce network bandwidth and computational requirements, Finally, we argue that projection aggregations represent a general-purpose framework for representing all simulation entities, thereby supporting evolution of entity models.