## 4 DSM, Orthomosaic and VR Scenario Building
### Photogrammetry Processing for UAV-Captured Pictures  
The 3D model for Metaxa Mine has been produced using Agisoft METASHAPE photogrammetry software ([[http://www.agisoft.com/](http://www.agisoft.com/)]([http://www.agisoft.com/](http://www.agisoft.com/))), a commercial SfM software characterized by a user-friendly interface and clear workflow with a reasonable price of the educational license and, much more importantly, good quality of the resulting SfM-derived models [28; 29; 30]. Processing has been performed using the Agisoft Cloud beta service, where the virtual machine is equipped as follows: CPU-32 vCPU (2.7 GHz Intel Xeon E5 2686 v4), GPU 2 \(\times\) NVIDIA Tesla M60, RAM 240 GB. Hereunder we describe the steps we adopted to produce the 3D tiled model, DSM and Orthomosaic, following a common workflow designed by previous authors [65; 66; 27]; we also applied new settings suggested in the Agisoft METASHAPE forum, especially to work with Oblique pictures. In any case, before running the workflow, all pictures acquired with Oblique orientation need to be prepared. As shown in Figure 5b, the sky shows in the picture; therefore, it had to be masked and removed by processing; it can be masked directly in Agisoft METASHAPE, after uploading all pictures, using Magic Wand Intelligent Scissors tools. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & **Mission 1** & **Mission 2** & **Mission 3** & **Mission 4** & **Mission 5** & **Mission 6** & **Mission 7** & **Mission 8** \\ \hline \multirow{6}{*}{**Captured**} & \multirow{2}{*}{Flying Date} & 14/10/2018 & 14/10/2018 & 16/10/2018 & 16/10/2018 & 16/10/2018 & 16/10/2018 & 17/10/2018 \\  & & Flying Height (m) & 30 & 30 & 30 & 30 & 30 & 30 & 30 \\  & & Frontal Overlap (\%) & 90 & 90 & 90 & 90 & 90 & 90 & 90 \\  & & Lateral Overlap (\%) & 85 & 85 & 85 & 85 & 85 & 85 & 85 \\  & & Flight Speed (m/s) & 1.6 & 1.6 & 1.6 & 1.6 & 1.6 & 1.6 & 1.6 \\  & & Shutter Interval (s) & 2 & 2 & 2 & 2 & 2 & 2 & 2 \\  & & Ground Resolution (cm/pix) & 0.9 & 0.9 & 0.9 & 0.9 & 0.9 & 0.9 & 0.9 \\  & & Flying Time (mins) & 19 & 21 & 19 & 20 & 19 & 17 & 18 & 15 \\  & & Covered Area (m\({}^{*}\)) & 16,633 & 18,824 & 17,048 & 16,325 & 4899 & 12,751 & 12,620 & 687 \\  & & Images Numbers & 554 & 567 & 485 & 584 & 486 & 522 & 447 & 251 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: UAV survey dates and detailed flight acquisition parameters for missions with nadir camera orientation. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & **Mission 1** & **Mission 2** & **Mission 3** & **Mission 4** \\ \hline \multirow{6}{*}{**Captured**} & \multirow{2}{*}{Flying Date} & 14/10/2018 & 14/10/2018 & 17/10/2018 & 17/10/2018 \\  & & Flying Height (m) & 10 \(\pm\) 40 & 10 \(\pm\) 40 & 10 \(\pm\) 40 & 10 \(\pm\) 40 \\  & & Gimble orientation & \(-45^{\circ}\) \(\pm\)\(-70^{\circ}\) & \(-45^{\circ}\) \(\pm\)\(-70^{\circ}\) & \(-45^{\circ}\) \(\pm\)\(-70^{\circ}\) & \(-45^{\circ}\) \(\pm\)\(-70^{\circ}\) \\  & & Flight Speed (m/s) & 1-2 & 1-2 & 1-2 & 1-2 \\  & & Shutter Interval (s) & 2 & 2 & 2 & 2 \\  & & Flying Time (mins) & 21 & 21 & 19 & 13 \\  & & Images Numbers & 504 & 579 & 471 & 344 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: UAV survey dates and detailed flight acquisition parameters for missions with oblique camera orientation. The first step consisted of aligning all pictures using low quality settings and generic preselection. In this step, focal length and photo dimensions were automatically computed by the software and then used for the subsequent calibration of the core parameters of the camera (principal point coordinates, lens distortion coefficients). In the second step, we added all GCPs to the model to obtain a scaled and georeferenced point cloud to improve the accuracy of the final models. Then, the images were realigned using high accuracy settings and 15,000 and 150,000 as limit values for Tie and Key points settings, respectively.