One of the key-features of the majority of VR systems is the support of real-time interactive graphics. As a result of this there is a great deal of common ground between computer animation research and VR research.
To support interactive animation, the process of object movement and update must be highly efficient. Work on the REALISM system has resulted in a highly efficient collision detection process that can be used for complex environments.
The system also supports many kinds of object in a scene, some of which may be explicitly controlled by users, giving an environment where there is no distinction between autonomous entities and actual users. This, combined with the ability to define a real-time limit for the frame update operations, means that the REALISM system is easily extended to support interactive animation.
Realistic object models that exhibit the necessary features for existence in a virtual environment are a prerequisite for convincing VR systems. The REALISM system provides libraries of predefined geometries, materials and behaviours that can be used to create the required objects. Each geometric object has an associated material that defines not only its visual appearance but its physical properties.
Object models are easily extendible, and their behaviour can be defined by the use of rules and constraints. The use of Java to drive VRML provides a rich environment within which it is easy to extend and adapt object behaviours dynamically. Work is currently centred on providing a mechanism for supporting automatic locations and use of Java classes by autonomous animated objects.
Most current VR systems support only simple polygonal models. This is primarily because the focus of the CG world has been on the polygon as the primary building block. Alternative approaches such as using implicit models offers more flexibility and in many cases provides a much simpler definition of complex models. The Implicit Modelling Working Group's aim is to extend VRML to support implicit models.
Whilst support for real-time interaction is one issue, the ability to supply updated images at a sufficient rate for convincing VR is another. Obviously, the primary requirement for this is high-performance hardware, but software that takes advantage of this is essential. To allow the use of parallel hardware schemes, the REALISM system has been extended in the ACE system. This has been developed to increase the speed of the generation of frame-based animation by dividing the total work for a given frame on an object basis (i.e. allocating a certain number of simulated objects to each processor). The system also supports all the features necessary for real-time interaction, and work is currently underway to increase this support to give an even more efficient animation system for use in interactive applications.
Author: I.J.Palmer
Last update: 20/04/97