| Ralf-Peter Mundani
| creator |
Mundani, Ralf-Peter
| | Bungartz, Hans-Joachim
| | date |
2004-06
| | | | description |
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.
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