Octrees - hierarchical data structures based on recursive substructuring - have turned out to be a powerful representative of the hierarchical paradigm, advantageous in a large variety of applications such as visualisation, computer graphics, databases resp. data mining, mesh generation, numerical simulation, or Geographic Information Systems (GIS). In this paper, octrees are used to build up a framework for the integration of CAD, simulation, and visualisation tasks from the field of structural engineering in a network-based cooperative working environment. It will be shown that, by providing octree-based tools, the coupling of these tasks and the control of the entire design process can be improved and simplified.

Starting from a CAD model, due to a new method based on the intersection of half-spaces, an octree representation can be efficiently derived, if necessary also in real time more details). A linearisation followed by a binary encoding of such trees results in streams that can be assigned to Boolean operators or more sophisticated tools for further processing - even on-the-fly. As such streams can be described by a Chomsky-II-grammar, their integrity - e.g. after transmission over a network - can easily be checked by a corresponding finite state automaton. Based on octree encoded streams, tools for various purposes like providing interfaces between different applications (e.g. CAD and numerical simulation tasks such as computational fluid dynamics) or collision detection between single parts of a geometric model, for instance, are possible.

Furthermore, to ensure global consistency of shared data processed by several experts in a network-based cooperative working environment, for instance, a geometric model is stored in a Relational Database Managment System (RDBMS) which can only be accessed by an octree and corresponding check-in/check-out functions. Thus, any modified parts intended to be written to the RDBMS and conflicting with the rest of the data can easily be detected. As octrees - because of their inherent hierarchy - also allow access to the data on different resolutions levels (e.g. walls, rooms, or floors), even conflicts among various processes can be detected and, hence, entire design processes can be coordinated and improved.

Another application scenario - visualisation and virtual reality - is also covered by this framework. Here, the former discussed model can be augmented by any arbitrary data (e.g. room informations), and a graph for shortest-path algorithms can automatically be derived and manipulated, meant for viewing both as VRML application within a web browser and as immersive stereo projection on more sophisticated devices like a power wall or a CAVE.

Summarising, the usage of an octree-based framework for the integration of processes from the field of structural engineering not only bridges the gap between the different applications like CAD, simulation, and visualisation, it also simplifies and improves the control abilities of these processes as a fundamental in a network-based cooperative working environment.