The growing complexity of urban environments has intensified the need for accurate 3D city models to support simulations and analyses in various fields such as urban planning, energy demand, and computational fluid dynamics (CFD). However, these models often contain geometric and topological errors, such as non-watertight solids, intersecting volumes, and missing surfaces, limiting their usability. This thesis presents AUTOr3pair, an automatic framework designed to repair semantic 3D city models and address these issues.

The process begins with validating 3D city models using val3dity, which ensures geometric validity based on ISO 19107 standards. Errors are addressed hierarchically, starting with ring-level fixes and progressing to solid interaction-level corrections, focusing on localized repairs to minimize alterations while preserving geometric and topological integrity. Existing repair methods are integrated alongside new algorithms designed to meet the specific needs of different use cases, including visualization, energy demand estimation, solar potential analysis, and CFD simulations. Written in C++ for optimal performance, the framework supports CityJSON and OBJ. The repairs prioritize maintaining semantic consistency and minimizing data loss, but textures are excluded. This approach results in a robust validation and repair pipeline that generates detailed error reports and post-processing outputs, significantly improving the overall quality of 3D city models.

Extensive tests on real-world datasets, including 3DBAG tiles from Leiden and a dataset from Brussels, demonstrated that AUTOr3pair successfully repaired most geometric errors, raising validity rates to nearly 100%.
The framework achieved additional requirements, such as watertight geometry and proper surface orientation, for the specific use cases, CFD, energy demand, visualization, and solar power estimation. While some floating-point errors and geometric differences, due to global repairs, persist in complex cases, AUTOr3pair significantly reduces manual pre-processing and improves model suitability for various applications.

This thesis demonstrates that automatic geometry repair is feasible and essential for improving the quality and usability of 3D city models. It provides a foundation for further research and development, particularly in extending the framework to support more file types and refining its capabilities for additional use cases.

The outcome of the project has been successful from the interpolation perspective, where the final results have shown major improvements over the original rasters, and a multitude of possible other interpolation methods have shown potential. In the end, the algorithm used to create the gridded DTM was
based on Startin’s Laplace interpolation and for DSM a Python implementation of quadrant-based IDW was used. The Startin Laplace method gives statistically good results while running quickly on it’s Rust base, though using quite some memory. The quadrant-based IDW has proven to be the best way to interpolate results which include the buildings, creating crisp edges without too many artefacts. Fur-
thermore, the introduction of a polygon water flattening step was essential to prevent no-data values where water bodies prevented for accurate interpolation. The long-shot goal of being able to process all the tiles for the Netherlands was missed by a lot, eventually choosing to interpolate a series of tiles neighboring Delft to create a contiguous result set. Zuid-Holland has therefore only been partially completed, whereas the expectation was to be able to complete this area with ease in three days. An initial overview of the comparison for a single tile in Rotterdam (37HN1), can be seen in Figure 1.3 for the DTM results and Figure 1.4 for the DSM results.