Ideally, virtual worlds should be dynamic, mutable, and complex in order to be attractive for immersed users. As such worlds can be designed easily by rewriting techniques, we propose a distributed Virtual Reality (VR) system that is based on an interactive animation system using a rewriting technique for geometric and behavioral modeling. The emphasis is on concepts and extensions for the integration of user immersion, user interaction, and networking into a rewriting-based animation system, Finally, the modeling of a ball game with two immersed users, as well as a virtual park, serve as case studies to illustrate the proposed concepts and extensions.

In computer graphics L-systems represent a powerful rule-based language for modeling complex objects and their animation. However, designing objects and animations by rules is a difficult task because designers often cannot foresee the consequences of rules. This is especially true for non-experts in the domain. Therefore, we propose to enhance an L-system based animation system with evolutionary features based on genetic algorithms (GAs). These features support the designers' task of interactively modeling objects and animations. Starting from an initial population of L-system-defined objects, the computer proposes iteratively new populations based on fitness value that are determined by the designers' creative or functional criteria. Moreover, automatic optimization of L-system-defined objects/animations is possible if an appropriate fitness function can be found for a given problem. We present a concept to integrate optimization by genetic algorithms into an L-system based animation system. Typical examples, such as automatic function optimization and creative interactive design of objects, illustrate our work.

We present a prototype system for a simple version of electromagnetic wave propagation prediction in rural areas, using a real time exploration environment for very large topographic scenes. The wave propagation prediction algorithm is based on a simple line of sight approach, realized with a modified hidden surface removal algorithm. The system serves as a transmitter management tool for interactively placing transmitters and studying the effects. Improvements according to the propagation prediction and automatic optimized placement of transmitters are current subjects of our research.

Advocates a desktop virtual reality (VR) interface to a geographic information system (GIS). The navigational capability to explore large topographic scenes is a powerful metaphor and a natural way of interacting with a GIS. VR systems succeed in providing visual realism and real-time navigation and interaction, but fail to cope with very large amounts of data and to provide the general functionality of information systems. We suggest a way to overcome these problems. We describe a prototype system, called ViRGIS (Virtual Reality GIS), that integrates two system platforms: a client that runs the VR component interacts via a (local or wide area) network with a server that runs an object-oriented database containing geographic data. For the purpose of accessing data efficiently, we describe how to integrate a geometric index into the database, and how to perform the operations that are requested in a real-time trip through the virtual world.

This paper describes how, in spite of occasional performance limitations generally due to process defects, large-area solid-state image sensors can be applied to scan pictorial data. First, it is estimated to what extent the direct imaging of pictorial matter onto a defective area-scanning device for acceptable scanning quality is possible. A novel concept is then proposed in which the optically generated Fourier-transform hologram of a picture rather than the picture itself is imaged onto a defective solid-state photosensitive array, scanned, digitized, filtered, and reconstructed by fast Fourier transform (FFT) techniques on a digital processor. The operating principle is discussed and the effects of scanner defects, digitization, and filtering on the scanning quality are investigated by computer simulation.

It is the evaluation of the subjective fidelity which is of primary importance in any communication system where humans constitute the final information receiver. A method showing how to generate grey-tone increments by computer for displaying simulation results is described. The method is based on the fact that, by over-printing well-defined characters of a commercially available chain printer, grey tones can be produced. The set of characters and the number of overprints used is presented in matrix form.