TLS and UAV Photogrammetry for As-Built Mapping of Wastewater Treatment Infrastructure: A Comparative Assessment and Retrospective Source Selection Approach

Terrestrial laser scanning (TLS) and unmanned aerial vehicle (UAV) photogrammetry provide complementary observations for infrastructure documentation, but their suitability depends on the required map features. This study compares TLS- and UAV-derived as-built products for a wastewater treatment plant with a conventional survey reference and illustrates a preliminary, retrospective, feature-level data source selection approach. Positional agreement was assessed at 30 independent check points selected purposively from details identifiable in all three products. RMSE3D was 7.51 cm for TLS and 7.66 cm for UAV; these values characterize the common observable sample rather than the accuracy of the complete infrastructure. TLS and UAV mapped 128 and 102 of 135 reference objects, corresponding to object detection completeness rates of 94.8% and 75.6%, respectively. UAV required less recorded acquisition effort, while TLS recovered more reference objects using the tested configuration. A transparent score combines planimetric accuracy and object detection completeness where both are available, with source eligibility assessed separately. The application illustrates source comparison using existing products; it does not establish improved map quality or lower production cost. A completed selected source map and a merge-all alternative were not independently evaluated.