This paper explores the issues involved in designing and developing network software architectures for large-scale virtual environments. We present our ideas in the context of NPSNET-IV, the first 3-D virtual environment that incorporates both the IEEE 1278 distributed interactive simulation (DIS) application protocol and the IP multicast network protocol for multiplayer simulation over the Internet.

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3D visual simulation systems must present a world, including terrain, cultural features and 3D icons, in real-time at a level of detail which supports the use for which the system is intended.A "simple" world lends itself to blasting all the polygons through the workstation's existing graphics pipeline. However, a "simple" world is not very realistic and/or does not operate in realtime. For complex worlds, such as that modeled in NPSNET, providing high fidelity in real-time requires the use of hierarchical data structures. We explore the implementation of such a structure on the world modeled by NPSNET utilizing quadtrees.

The Naval Postgraduate School (NPS) has actively explored the design and implementation of networked, real time, three-dimensional battlefield simulations on low-cost, commercially available graphics workstations. The most recent system, NPSNET, has improved in functionality to such an extent that it is considered a low-cost version of the Defense Advanced Research Project Agency's (DARPA) SIMNET system. To reach that level, it was necessary to economize in certain areas of the code so that real time performance occurred at an acceptable level. One of those areas was in aircraft dynamics. However, with “off-the-shelf” computers becoming faster and cheaper, real-time and realistic dynamics are no longer an expensive option. Realistic behavior can now be enhanced through the incorporation of an aerodynamic model. To accomplish this task, a prototype flight simulator was built that is capable of simulating numerous types of aircraft simultaneously within a virtual world. Besides being easily incorporated into NPSNET, such a simulator also provides the base functionality for the creation of a general purpose aerodynamic simulator that is particularly useful to aerodynamics students for graphically analyzing differing aircraft's stability and control characteristics. This system is designed for use on a Silicon Graphics workstation and uses the GL libraries. A key feature of the simulator is the use of quaternions for aircraft orientation representation to avoid singularities and high data rates associated with the more common Euler angle representation of orientation.