The continued growth in the complexity of apartment buildings, and the digitization of building processes have led to a rise in the use of BIM models during the architectural development phase. These models contain a lot of information, but their life cycle often ends once the building is constructed. However, this information can be used by the Dutch Cadastre, to bring legal building registration even closer to 3D reality. BIM based legal registration, researched under the name BIM Legal, is a key driver for this research. Currently in the Netherlands, the separation of ownership is registered through notarial deeds that are managed by the Dutch Cadastre. This is accompanied by division drawings that indicate how apartments are split into private apartment units and shared spaces.
To develop a full BIM Legal registration, it is necessary to also look at buildings without a BIM model. In such cases, BIM Legal models could be derived from existing legal documents, specifically division drawings. This research investigates the (semi-)automatic reconstruction of 3D legal apartment models from 2D vectorized division drawings. The proposed pipeline starts with already vectorized division drawings and applies shape-based georeferencing techniques, estimating storey heights, vertical alignment, and ends with generating 3D BIM Legal models.
The georeferencing methods tested achieved sufficient alignment across the 10 sample buildings. When outside spaces were included in the vectorized division drawing, it resulted in an average containment of 81.5%. When they were removed or non existing it resulted in 95.2% containment. Storey alignment relies on shape similarity and floor-to-floor matching, which performed well in typical cases but struggled with floors with low similarity to the floor below it. The accuracy of height estimation improves when cross sections are included in the division drawing. Otherwise averaged based on values retrieved from the 3DBAG.
The resulting models conform to the BIM Legal standard, written in CityJSON format at a LoD1+. While the schematic nature of division drawings limits the achievable level of detail, and the geometric and positional accuracy, the models offer a valuable 3D visualization of private and shared ownership spaces. Improvements to the prior vectorization would also improve the accuracy and computation time of the 3D reconstruction. Large scale testing is necessary to research the potential incorporation of BIM legal models from division drawings with a complete BIM Legal registration.
This research not only advances the automation of BIM Legal models from division drawings, but also provides methods which can be applied in other 3D reconstructions, such as georeferencing polygons with a reference to a cadastral dataset.
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With the development of technologies and people’s raising standards for both indoor and outdoor environments, buildings have expanded their functionalities of merely being human’s everyday sheltering place. Common modern building applications include but are not limited to Building Energy Modelling (BEM), solar potential estimation, wind simulations, shadow analysis, noise propagation, and digital building permit checking. Among all
the common building applications, many of them only need to use the building’s envelope (A building’s envelope is composed of all building elements that are exposed to the outdoor environment). It is apparent that building envelope extraction can be beneficial to these applications. Currently, building envelopes are mainly constructed from point cloud data or satellite image data. With the increased usage of Building Information Model (BIM) models within the Architecture, Engineering and Construction (AEC) industry, more attempts have been done on extracting building envelopes from BIM models as well. In addition, the BIM-based building envelope tool can be used throughout the building’s life cycle. However, previously developed BIM-based building envelope extraction tools all have different types of flaws. The main problem with the existing methods is separating the building envelope elements is difficult and time-consuming. Considering the benefits extracting building envelopes from BIM models can bring and the limitations of the developed methods, it is beneficial to develop a different BIM-based building envelope extraction approach that can produce high-quality building envelopes efficiently. Therefore, in this study, to avoid the difficult problem of separating building interiors and building exteriors, we first extract the point cloud from BIM models and then extract this point cloud’s exterior boundary using the 3D alpha shape algorithm, and therefore obtain the building envelope. The quality of the extracted building envelopes is evaluated by their geometric accuracy, simplicity, and time efficiency. Among them, the geometric accuracy is evaluated by the deviations between the extracted surfaces and the original surfaces. The simplicity is measured by the number of vertices and faces, and the time efficiency is measured by the building envelope extraction speed. The results show that despite the developed method has some limitations, it can extract building envelopes with high geometric accuracy from various types of small-scale BIM models. The main limitations include its inability to process big BIM models, the extracted building envelope merely contains its geometry without the enrichment of topological and semantic information. For all the tested BIM models, the average geometric accuracy is within 2.00cm. Walls and roofs are very accurately extracted, with errors of less than 0.01cm. Windows, doors, and other types of small-scale objects are extracted with a bigger error of
0.1m to 0.3m. The extracted building envelope also simplifies the input models significantly regarding the number of vertices and the number of faces. Lastly, for small-scale models, the developed building envelope extraction tool is able to process them within 150s.

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