Abstract
In this study, an analysis of the capabilities of unmanned aerial vehicle (UAV) photogrammetry to obtain point clouds from areas with a near-vertical inclination was carried out. For this purpose, 18 different combinations were proposed, varying the number of ground control points (GCPs), the adequacy (or not) of the distribution of GCPs, and the orientation of the photographs (nadir and oblique). The results have shown that under certain conditions, the accuracy achieved was similar to those obtained by a terrestrial laser scanner (TLS). For this reason, it is necessary to increase the number of GCPs as much as possible in order to cover a whole study area. In the event that this is not possible, the inclusion of oblique photography ostensibly improves results; therefore, it is always advisable since they also improve the geometric descriptions of break lines or sudden changes in slope. In this sense, UAVs seem to be a more economic substitute compared to TLS for vertical wall surveying.
Highlights
Topographical surveys of surfaces with high angles of inclination such as nearly vertical slopes on roads or motorways, as well as the survey on architectural facades, are a technical challenge, the main concern of which is ensuring the safety of the operators responsible for carrying out the survey
Once the point clouds are obtained by unmanned aerial vehicle (UAV) photogrammetry, they are compared with that obtained by terrestrial laser scanners (TLS)
For the seven profiles studied, the average of the mean differences is below 0.03 cm with a standard deviation of less than 3 cm, which ensures the correct georeferencing of the TLS point cloud
Summary
Topographical surveys of surfaces with high angles of inclination such as nearly vertical slopes on roads or motorways, as well as the survey on architectural facades, are a technical challenge, the main concern of which is ensuring the safety of the operators responsible for carrying out the survey. TLS measures the time of flight of an emitted laser pulse that is reflected off of an intervening feature and returned to the sensor, resulting in a range measurement [1]. Because lasers arrive directly at the surface of the object and are reflected from it, this technology can precisely acquire spatial coordinates with an error that depends on the range, which usually varies between 1 and 10 mm. There is a trend to complement this technology with unmanned aerial vehicles (UAVs) carrying digital cameras
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