Validation of a Commercial Ultrasonic Real-Time Location System for Providing Position Constraints in Low-Cost Indoor Photogrammetric Reconstruction

Indoor 3D reconstruction for building documentation faces a fundamental challenge: creating accurate, properly scaled digital models without relying on extensive ground control point (GCP) networks or specialized surveying expertise. This research investigates whether commercial ultrasonic real-time location systems (RTLS) can provide sufficiently accurate camera position constraints to eliminate GCPs in smartphone-based indoor photogrammetry while maintaining architectural documentation accuracy requirements (2–5 cm). The ZeroKey Quantum RTLS was validated through three progressive experimental phases using tripod-mounted data collection under controlled conditions. Repeatability assessment established optimal data collection protocols – a 1-second sliding window threshold-based approach following brief settling – and quantified measurement precision: the root mean square (RMS) position precisions were 1.6 mm (X), 1.7 mm (Y), and 1.1 mm (Z), and the RMS orientation precisions were 0.08° (ω), 0.09° (ϕ), and 0.07° (κ). Sparse reconstruction of signalized targets evaluated both position-only and combined position-and-orientation constraints. Position-only constraints demonstrated superior performance through 100% bundle adjustment convergence reliability and lower random errors, achieving inter-target distance RMS errors of 2.0–3.3 mm compared to terrestrial laser scan reference data after correcting for systematic scale errors. Critically, this systematic bias could be addressed using minimal ground control – as few as two GCPs – rather than extensive networks. Dense reconstruction of a complex indoor environment met the 2–5 cm accuracy requirements, achieving 11.6 mm RMS check point error while delivering 64% reduction in total processing time by eliminating manual GCP identification in images. The research establishes that commercial ultrasonic RTLS can successfully replace extensive GCP networks for indoor photogrammetric reconstruction while maintaining architectural documentation accuracy, providing a foundation for future work transitioning to handheld operation. The proprietary nature of the RTLS represents the primary limitation, preventing investigation of systematic error sources.