Joachim Benner

New Concepts for Structuring 3D City Models – An Extended Level of Detail Concept for CityGML Buildings

We propose a new Level of Detail (LoD) concept for CityGML buildings that differentiates a Geometrical Level of Detail (GLoD) and a Semantical Level of Detail (SLoD). These two LoD concepts are separately defined for the interior characteristics and the outer shell of a building, respectively. The City Geography Markup Language (CityGML) is an open and application independent information model for the representation, storage, and exchange of virtual 3D city models. It covers geometric representations of 3D objects as well as their semantics and their interrelation. The CityGML Level of Detail concept in general offers the possibility to generalize CityGML features from very detailed to a less detailed description. The current LoD concept suffers from strictly coupling geometry and semantics. In addition it provides only one LoD (LoD4) for the description of the interior of a building. The benefits of our new LoD concept are first, a substantially higher informative value for the Level of Detail, second, a better description of the interior Level of Detail, third, a broadening of the opportunities for indoor modelling, and last, a better assignability to all other modules represented in CityGML. Due to more combinations of GLoD and SLoD, the Level of Detail definition for every module in CityGML can be defined according to the nature of modelled real world phenomenon.

Generalization of 3D IFC Building Models

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 Energy Application Domain Extension for CityGML: enhancing interoperability for urban energy simulations

The road towards achievement of the climate protection goals requires, among the rest, a thorough rethinking of the energy planning tools (and policies) at all levels, from local to global. Nevertheless, it is in the cities where the largest part of energy is produced and consumed, and therefore it makes sense to focus the attention particularly on the cities as they yield great potentials in terms of energy consumption reduction and efficiency increase. As a direct consequence, a comprehensive knowledge of the demand and supply of energy resources, including their spatial distribution within urban areas, is therefore of utmost importance. Precise, integrated knowledge about 3D urban space, i.e. all urban (above and underground) features, infrastructures, their functional and semantic characteristics, and their mutual dependencies and interrelations play a relevant role for advanced simulation and analyses.As a matter of fact, what in the last years has proven to be an emerging and effective approach is the adoption of standard-based, integrated semantic 3D virtual city models, which represent an information hub for most of the above-mentioned needs. In particular, being based on open standards (e.g. on the CityGML standard by the Open Geospatial Consortium), virtual city models firstly reduce the effort in terms of data preparation and provision. Secondly, they offer clear data structures, ontologies and semantics to facilitate data exchange between different domains and applications. However, a standardised and omni-comprehensive urban data model covering also the energy domain is still missing at the time of writing (January 2018). Even CityGML falls partially short when it comes to the definition of specific entities and attributes for energy-related applications.Nevertheless, and starting from the current version of CityGML (i.e. 2.0), this article describes the conception and the definition of an Energy Application Domain Extension (ADE) for CityGML. The Energy ADE is meant to offer a unique and standard-based data model to fill, on one hand, the above-mentioned gap, and, on the other hand, to allow for both detailed single-building energy simulation (based on sophisticated models for building physics and occupant behaviour) and city-wide, bottom-up energy assessments, with particular focus on the buildings sector. The overall goal is to tackle the existing data interoperability issues when dealing with energy-related applications at urban scale.The article presents the rationale behind the Energy ADE, it describes its main characteristics, the relation to other standards, and provides some examples of current applications and case studies already adopting it.

3D Geoinformation Science

Nowadays 3D Geoinformation is needed for many planning and analysis tasks. For example, 3D city and infrastructure models are paving the way for complex environmental and noise analyzes. 3D geological sub-surface models are needed for reservoir exploration in the oil-, gas-, and geothermal industry. Thus 3D Geoinformation brings together researchers and practitioners from different fields such as the geo-sciences, civil engineering, 3D city modeling, 3D geological and geophysical modeling, and, last but not least, computer science. The diverse challenges of 3D Geoinformation Science concern new approaches and the development of standards for above- and under-ground 3D modeling, efficient 3D data management, visualization and analysis. Finally, the integration of different 3D approaches and data models is seen as one of the most important challenges to be solved.