Structure from motion of the Ichilo riverbanks in Puerto Villarroel, Bolivia

Structure from motion photogrametry was used to survey the banks of the Ichilo river, in the city of Puerto Villarroel in Bolivia. The surveyed areas was of aproximately 300 hectares of terrain. A DJI Phantom 4 Pro and a DJI Mavic Pro was used for taking pictures. A total of 44 GCPs were marked along the riverbanks of the Ichilo and their coordinates were measured using a Real-time Kinematic (RTK) GPS unit. After the GCPs were marked, the UAVs were launched and the pictures were taken including the GCPs and a total of 1358 pictures were taken during the surveys. The imagery was analysed and processed using the software Agisoft PhotoScan and orthophotos. The GCPs were split in in two groups: the first group with thirty GCPs were used to correct the imagery, and the other 14 were used to assess the accuracy of the imagery. The processed imagery taken in May, 2019 resulted in a orthomosaic and a digital elevation model (DEM). Also, particle size distributions of two samples taken in the the Ichilo river are presented.

Methods
A DJI Phantom 4 Pro and a DJI Mavic Pro was used for taking pictures. Details of the equipment, survey design and execution and other details are shown in the paper.  Before taking the imagery, we marked ground control points (GCPs) along the banks, wherever the access to the area was possible, in order to georeference the digital elevation model (DEM). The GCPs were white crosses (around 1m large) marked using latex painting that were easily visible in the aerial imagery. A total of 44 GCPs were marked along the riverbanks and their coordinates were measured using a Real-time Kinematic (RTK) GPS unit. After the GCPs were marked, the UAVs were launched and the pictures were taken including the GCPs and a total of 1358 pictures were taken during the surveys. The imagery was analysed and processed using the software Agisoft PhotoScan.The GCPs were split in in two groups: the first group with thirty GCPs were used to correct the imagery, and the other 14 were used to assess the accuracy of the imagery. The mean positional errors of the 14 reserved GCPs were 0.003, 0.004, and 0.06 m in the x, y and z directions, respectively. In addition, two granulometric samples are included in this dataset.