Semantically Enriched Voxels as a Common Representation for Comparison and Evaluation of 3d Building Models

Abstract

Abstract. 3D city models are fast becoming a key factor for planning, design and analysis in the AEC industry, and urban informatics. Data are being acquired from a variety of sources and each consequent representation contains inherent information about its location, geometry, structure and usability. These digital representations can range from unstructured models with very little semantic data such as 3D point clouds, and 3D mesh models or they can be highly structured and semantically enriched models following CityGML and IFC/BIM standards. Matching these diverse representations against one another can facilitate information flow and eventually lead to a coherent interconnected Digital twin. Consistency measures would be needed to compare one representation against another. For comparison of any kind, a common baseline needs to be established. A tentative approach, as outlined in this paper, is to convert all the model types into a common representation such as ‘volumetric pixels’ or ‘voxels’ but the concept of ‘voxel’ as we know it, is not enough to deal with the rich semantic and organizational structure of modelling representations such as IFC and CityGML. Voxelisation is a complex process and conventional conversion methods concentrate on translating the geometry between representation types but the semantic and class hierarchy information is usually not translated. This paper assesses the need for matching 3D models using a common representation (voxels), discusses the challenges of the voxelisation process and proposes the concept of a ‘RichVoxel’.

Artificial Intelligence for the Automated Creation of Multi-scale Digital Twins of the Built World—AI4TWINNING

“…Voxels are an ideal primitive that support most of the above mentioned criteria as seen in [11]. RichVoxel models [6] as a common representation to match the different 3D city/building models Voxels in the field of 3D city modelling and urban research are not a new concept. Voxels have been used in various BIM/GIS applications such as path planning as seen in [9], as volumetric modelling primitives [10], for space planning and semantic segmentation of 3D point clouds, [12], etc.…”

“…of a voxel as it exists is not enough to deal with the semantic organisation of city models especially those that follow the international standards of CityGML and IFC. For this, [6] have developed the concept of a RichVoxel or a 'Semantically Enriched Voxel' which can map the information from the modelling aspects of all other representation types without loss of information.…”

“…11) models. Once voxelised, the models are initially compared against the level of semantic information (explained in [6]) and a common baseline is established. The models are also compared against their spatial and semantic extents followed by a component to component match than an individual voxel match.…”

A Concept for 3D Geological and Urban Subsurface Modeling with a Unified Voxel Model Examined by a Case Study for the City Center of Stuttgart (Baden-Württemberg), Germany

“…As some use cases demonstrate, the conversion of these geometries into a voxel model and the parameterization of individual voxels are common modeling approaches. The conversion of semantic-rich CityGML and IFC datasets can only be achieved through time-consuming and computationally intensive workflows (Heeramaglore and Kolbe, 2022).…”