UAV survey of a coastal cliff face – Selection of the best imaging angle. Jaud, M., Letortu, P., Théry, C., Grandjean, P., Costa, S., Maquaire, O., Davidson, R., & Le Dantec, N. 139:10–20.
UAV survey of a coastal cliff face – Selection of the best imaging angle [link]Paper  doi  abstract   bibtex   
UAVs are relevant for monitoring cliff faces. In this study, several flights are performed with various imaging angles (nadir, 20°, 30° and 40° off-nadir) to assess the impact of the imaging angle on the 3D cliff face reconstruction. Occlusions issues arising with sub-vertical cliffs make nadir surveys nearly irrelevant. The results obtained with 20°, 30° and 40° off-nadir imaging angles are satisfactory regarding texture restitution and accuracy with respectively 5.5 cm, 5.9 cm and 4.9 cm of error, higher tilting angles yielding better reconstructions on sub-vertical or overhanging parts of the cliff. This article also investigates other parameters affecting tiepoint detection on the cliff face, as the effective overlap, the UAV-cliff face distance and the cliff face illumination. Guidelines are provided for UAV survey parameterization, aiming at capturing the whole cliff face with a good trade-off between distance to the cliff, flight height and spatial resolution of the photographs.
@article{jaud_uav_2019,
	title = {{UAV} survey of a coastal cliff face – Selection of the best imaging angle},
	volume = {139},
	issn = {0263-2241},
	url = {http://www.sciencedirect.com/science/article/pii/S0263224119301435},
	doi = {10.1016/j.measurement.2019.02.024},
	abstract = {{UAVs} are relevant for monitoring cliff faces. In this study, several flights are performed with various imaging angles (nadir, 20°, 30° and 40° off-nadir) to assess the impact of the imaging angle on the 3D cliff face reconstruction. Occlusions issues arising with sub-vertical cliffs make nadir surveys nearly irrelevant. The results obtained with 20°, 30° and 40° off-nadir imaging angles are satisfactory regarding texture restitution and accuracy with respectively 5.5 cm, 5.9 cm and 4.9 cm of error, higher tilting angles yielding better reconstructions on sub-vertical or overhanging parts of the cliff. This article also investigates other parameters affecting tiepoint detection on the cliff face, as the effective overlap, the {UAV}-cliff face distance and the cliff face illumination. Guidelines are provided for {UAV} survey parameterization, aiming at capturing the whole cliff face with a good trade-off between distance to the cliff, flight height and spatial resolution of the photographs.},
	pages = {10--20},
	journaltitle = {Measurement},
	shortjournal = {Measurement},
	author = {Jaud, Marion and Letortu, Pauline and Théry, Claire and Grandjean, Philippe and Costa, Stéphane and Maquaire, Olivier and Davidson, Robert and Le Dantec, Nicolas},
	urldate = {2019-11-26},
	date = {2019-06-01},
	langid = {english},
	keywords = {Normandy, Cliff face erosion, Coastal monitoring, {SfM} photogrammetry, Tilted camera, {UAV}}
}
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