Quality Evaluation of Digital Twins Generated Based on UAV Photogrammetry and TLS: Bridge Case Study

Compares point-cloud 'digital twins' of an 1893 heritage timber truss bridge in Australia built from UAV photogrammetry and terrestrial laser scanning (TLS). Quality was assessed by plane and cylinder fitting, cloud-to-cloud distance, profiles, point density and scale error. The UAV cloud reached millimetre-level agreement on many measures, but had about half the TLS point density and centimetre-level scale error.

Key findings

• About 349 million UAV points versus over 1,590 million TLS points
• Plane fitting RMSE about 1.96 mm (UAV); cylinder fitting STD/RMSE above 4 mm (UAV) vs below 3.4 mm (TLS)
• Cloud-to-cloud mean differences under 4.5 mm for piers and under 8.5 mm for another part
• UAV scale error at centimetre level versus millimetre level for TLS; TLS density roughly double

Limitations

• Single bridge, only a middle section analysed
• TLS treated as ground truth
• UAV GNSS can degrade under the bridge
• Effects of survey planning and processing settings left for future work