Centimetre-range deformations of built environment revealed by drone-based photogrammetry

Deformation monitoring is an important component of the construction process and maintenance. Conventional point-wise surveying methods, however, tend to be time consuming, labour-intensive and may pose a risk to the surveyors. Instead, unmanned aerial vehicles in combination with structure-from-motion photogrammetry are now capable of high-accuracy contactless surveys. This study hence investigates road structure deformations identifiable by drone surveys from 40, 50 and 60 m flight altitudes. The surveys were georeferenced in 21 different ground control point configurations using integrated georeferencing. Comparisons between the resulting models and terrestrial laser scanning ground truth yielded the optimal configurations. The determined deformation estimates by using the optimal georeferencing configurations were validated using high-precise levelling results, which yielded the best deformation residual RMSE estimate of 0.29 cm for the 50 m altitude survey. These tests demonstrated that the proposed method can be employed for quick and contactless quantification of magnitude of built environment deformations.