Today, Building Information Modeling (BIM) is mainly used in architecture. Typically, a BIM model contains detailed geometric and semantic information for design evaluation, simulation, and construction of the building. If, as on the regional and city levels, more than one building is considered, the information content of detailed BIM models might be too high. For applications like noise simulation or emergency management, representing buildings as block models, reduced outer-shell models or simplified indoor models are more suitable. Such models are typically found in Geospatial Information System (GIS) applications. This paper describes a process for BIM building models to extract different generalized representations for buildings and building elements. As an example, the definitions for such representations are based on the LoD concept of CityGML.
The Open Geospatial Consortium (OGC) <i>CityGML</i> standard offers a Level of Detail (LoD) concept that enables the representation of CityGML features from a very detailed to a less detailed description. Due to a rising application variety, the current LoD concept seems to be too inflexible. Here, we present a multi representation concept (MRC) that enables a user-defined definition of LoDs. Because CityGML is an international standard, official profiles of the MRC are proposed. However, encoding of the defined profiles reveals many problems including mapping the conceptual model to the normative encoding, missing technologies and so on. Therefore, we propose to use the MRC as a meta model for the further definition of an LoD concept for CityGML 3.0.
ABSTRACT:Virtual 3D city models contain digital three dimensional representations of city objects like buildings, streets or technical infrastructure. Because size and complexity of these models continuously grow, a Level of Detail (LoD) concept effectively supporting the partitioning of a complete model into alternative models of different complexity and providing metadata, addressing informational content, complexity and quality of each alternative model is indispensable. After a short overview on various LoD concepts, this paper discusses the existing LoD concept of the CityGML standard for 3D city models and identifies a number of deficits. Based on this analysis, an alternative concept is developed and illustrated with several examples. It differentiates between first, a Geometric Level of Detail (GLoD) and a Semantic Level of Detail (SLoD), and second between the interior building and its exterior shell. Finally, a possible implementation of the new concept is demonstrated by means of an UML model.
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