While surface-oriented models became more and more popular because of their flexibility concerning manipulation, especially within CAD applications, they are only conditionally suited for simulation or controlling tasks, a field still dominated by volume-oriented models. Due to their spatial decomposition of the underlying geometry, volume-oriented models provide an easy access to simulation tasks relevant in civil engineering like air conditioning of rooms, statics analysis of buildings, or managing and controlling design processes. Here, hierarchical recursive data structures like octrees seem to be perfectly suited to efficiently bridge the gap between classical CAD applications on the one side and volume-oriented tasks as mentioned above on the other side. Within our research, a global geometric model represented by an octree is the starting point of a network-based cooperative working environment, allowing us a fast and efficient control of collision detection and model revision as well as the integration of different simulation tasks or disciplines like architecture and civil engineering, for instance.

For a fast derivation - even on-the-fly - of a volume-oriented model from a surface-oriented one, the octrees are generated by intersecting half-spaces that come from single flat surface patches of the original CAD model, provided in the (Eurostep) IFC format. As only convex objects can obviously be processed by this method, non-convex objects have to be decomposed into convex parts in advance. For a convex decomposition, such an object's convex hull is recursively calculated, marking all faces lying on the convex hull and processing the rest in the same way until all faces are labelled. With respect to these labels, an expression consisting of the three Boolean operators union, difference, and intersection is formed, describing a unique order to process the corresponding half-spaces. Hence, the result is an (volume-oriented) octree representation of the original surface-oriented geometry.

A linearisation and binary encoding of these octrees result in bit streams to which different operators like collision detection, for instance, can be applied. Any inconsistencies can be easily detected to be removed by the respective expert. Thus, the consistency of the global geometric model is ensured. For a cooperative work, the global geometric model is stored in a Relational Database Management System (RDBMS), accessed by a second control octree storing the primary keys to the RDBMS's tables, such that neighbouring elements or collisions between revised elements can be detected in a fast and efficient way. The cooperative work is further supported by several check-in/check-out methods, providing different levels of granularity concerning notifications being sent to all participating experts based on their actual processed elements as well as typical read-only, read-write, and exclusive-write permissions for each element.

The usage of octrees as integral element in a network-based cooperative working environment not only simplifies the control and combination of different tasks, it can also work as common interface between several disciplines - e.g. architecture and civil engineering - to bring us one step closer to the long-term objective of completely embedded simulation processes.