Generation of precise 3D building models for digital twin projects using multi-source data fusion and integration into virtual tours

High-quality production of building digital twins (DT) is always a challenging issue. In this study, a methodology is proposed to obtain a precise georeferenced 3D building model with high geometric and spectral quality, which is one of the essential components of a high-quality DT production, through the fusion of UAV and terrestrial photogrammetric data. To better evaluate the performance of the proposed methodology a complex building with glass facades, entrance porches, outdoor stairs, and architectural coverings was chosen. The techniques, used for overcoming the challenging issues about multi-source image orientation, spectral enhancement and precise building model production were presented. In the proposed methodology, distinct from the existing literature studies, photos obtained from different sources were not merged in an image-pool before photogrammetric processing, and geometric and spectral calibrations of aerial and terrestrial photos are completed separately before data fusion. In this manner, individual dense point clouds were both generated based on structure from motion (SfM) and made noise-free with filtering in Bentley ContextCapture software. Precise 3D building model production involved first merging the geo-referenced point clouds, followed by 3D model generation from the fused cloud. The production methodology involved first merging the geo-referenced point clouds, followed by 3D model generation from the fused cloud. The building model was achieved with the geometric accuracy (RMSE) of ≤ ±2 cm by the fusion of ±1.87 cm and ±1.17 cm accuracy UAV and terrestrial photogrammetry dense point clouds, respectively. In addition, an indoor model was generated by capturing 360° panoramic photos of the building and a complete virtual tour was created by merging indoor and outdoor data in the Unity game engine platform.