## 3 Results
### Depth Survey and 3D Modelling Test Results  
This section reports the data to evaluate the sonar performance in depth measurement and the 3D modelling methods. Table 13 shows the data collected to evaluate the performance of the Deeper Smart Sonars CHIRP+ and Pro+ 2 in measuring depth. The measured depths were 0.9 m and 1.52 m, in fresh and sea water (salinity 37.8%). The value of \(\Delta\)V represents the difference between the mean of the measured depth value considering 3700 samples and the real depth value, \(\sigma\)V is the standard deviation of the measured values. To evaluate the accuracy and precision of the 3D models produced, a comparison based on Cloud-To-Mesh (C2M) distance was performed in CloudCompare (Table 14). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Path Length (m)** & **Device** & **Positioning** & **\(\mu\)2D (m)** & **\(\sigma\)2D (m)** & **THU (m)** \\ \hline \multirow{4}{*}{\(\sim\)11.50 linear} & Deeper GNSS Pro+ 2 & SPP & 0.700 & 0.482 & 1.180 \\ \cline{2-6}  & \multirow{4}{*}{G \(>\) S \(>\) P Sys} & SPP & 1.034 & 0.095 & 0.232 \\  & & PPP-kinematic & 0.640 & 0.092 & 0.226 \\  & & PPK & 0.043 & 0.031 & 0.075 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Performance in the GNSS kinematic planimetric positioning of the Deeper Smart Sonar CHIRP+, the Deeper Smart Sonar Pro+ 2 and the G \(>\) S \(>\) P Sys in the sea test. Figure 14: Comparison of the GNSS kinematic positioning of the G \(>\) S \(>\) P Sys in the pool tests: (a) planimetric SPP; (b) planimetric PPP-kinematic positioning; (c) planimetric PPK positioning; (d) 3D P; (e) 3D PPP-kinematic positioning, (f) 3D PPK positioning. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Device** & **Real depth (m)** & **Water** & \(\Delta\)**V (m)** & \(\sigma\)**V (m)** & **TVU (m)** \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} Deeper Smart \\ Sonar CHIRP+ \\ \end{tabular} } & \multirow{3}{*}{0.9} & Fresh & 0.02 & 0.00 & 0.00 \\  & & Salt-37.8\% & 0.02 & 0.02 & 0.04 \\ \cline{2-6}  & \multirow{3}{*}{1.52} & Fresh & 0.01 & 0.00 & 0.00 \\  & & Salt-37.8\% & 0.01 & 0.11 & 0.21 \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Deeper Smart \\ Sonar Pro+ 2 \\ \end{tabular} } & \multirow{3}{*}{0.9} & Fresh & 0.03 & 0.00 & 0.00 \\  & & Salt-37.8\% & 0.02 & 0.02 & 0.04 \\ \cline{1-1} \cline{2-6}  & \multirow{3}{*}{1.52} & Fresh & 0.02 & 0.00 & 0.01 \\ \cline{1-1}  & & Salt-37.8\% & 0.04 & 0.06 & 0.12 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Performance in depth measurement of Deeper Smart Sonar CHIRP+ and Deeper Smart Sonar Pro+ 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model** & **Example Images** & **Interpolation Method** & \(\mu\)**3D (m)** & \(\sigma\)**3D (m)** \\ \hline \multirow{3}{*}{\begin{tabular}{c} 3D model FCR \\ – natural surface \\ \end{tabular} } & Forest-based & & \\  & Classification and & & 0.0020 & 0.0323 \\ \cline{1-1}  & Regression & & & \\ \hline \multirow{3}{*}{\
\begin{tabular}{c} 3D model OK \\ natural surface \\ \end{tabular} } & Ordinary Kriging & 0.0043 & 0.0283 \\ \cline{1-1}  & & & \\ \hline \multirow{3}{*}{
\begin{tabular}{c} 3D model IDW \\ natural surface \\ \end{tabular} } & IDW & 0.0059 & 0.0317 \\ \cline{1-1}  & Linear interpolation & 0.0124 & 0.0245 \\ \cline{1-1} \cline{2-6}  & Linear interpolation & 0.0002 & 0.0140 \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Mean and standard deviation values of C2M distance of seabed and pool models. For the seab (the natural surfaces), the comparison was carried out between the 3D model FCR, the 3D model OK and the 3D model IDW, and 40% of the points that were selected for the final validation. In the case study of the pool (the artificial structure), a comparison was conducted between the 3D model created by the proposed 3D modelling method and the model reconstructed by the traditional survey. Furthermore, regarding the swimming pool, the C2M was performed both on the entire structure and only on the bottom.