## 3 Results
### Assessing Accuracy of DSM  
The accuracy of DSMs was assessed through the differences between the VP coordinate (Z) and coordinate extracted from the BBA_traditional and BBA_PPK methods. Table 5 shows the basic results for difference statistics for Z coordinate and the final RMSE\({}_{\rm Z}\) values. The differences range from \(-0.079\) m (Krnica) to \(0.165\) m (Krnica) in the case of BBA_traditional, while the differences with BBA_PPK were higher; they range from \(-0.129\) m (Krnica) to \(0.453\) m (Mangart). The mean value of differences ranges from \(-0.022\) m (Mangart) to \(0.026\) m (Krnica) in the case of BBA_traditional. The mean value of differences with BBA_PPK were higher, and range from \(-0.002\) m (Krnica) to \(0.244\) m (Mangart). The standard deviations of the differences were the same for both BBA methods at the Kekec site (0.037 m), while larger differences in standard deviation were present at the Krnica (0.055 m for BBA_traditional, 0.072 m for BBA_PPK) and Mangart site (0.021 m for BBA_traditional, 0.093 m for BBA_PPK). RMSE\({}_{\rm Z}\) was generally smaller in the case of the BBA_traditional method; however, in comparison to the BBA_PPK method for the Kekec and Krnica, the difference was only \(0.027\) m and \(0.012\) m, respectively. Larger differences in RMSE\({}_{\rm Z}\) were presented for the Mangart rockfall, namely they reached \(0.231\) m. The frequency distribution of the Z coordinates (Figure 8) indicates that DSM produced with BBA_traditional achieved the lowest differences, while the values had larger span, compared to the assessment of BBA alone. The differences of BBA_traditional and BBA_PPK coincided in a larger part of the frequency distribution, with the latter achieving larger differences. The results were, similar as with the assessment of BBA and orthomosaic, different at the Mangart location; where, for the DSM produced with BBA_PPK, the differences were larger and had greater span than those ones produced with BBA_traditional. Moreover, the differences did not coincide at all at the Mangart location. To test for statistically significant differences in the mean value of differences between the BBA_traditional and BBA_PPK, a paired Student's \(t\)-test was used for diff\({}_{\rm Z}\) at the Krnica and Mangart site. It showed that there were statistically significant differences in the mean \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Units in m** & \multicolumn{3}{c}{**KEKEC**} & \multicolumn{3}{c}{**KRNICA**} & \multicolumn{3}{c}{**MANGART**} \\ \cline{2-7}  & **DSM\_Traditional** & **DSM\_PPK** & **DSM\_Traditional** & **DSM\_PPK** & **DSM\_Traditional** & **DSM\_PPK** \\ \hline diff\({}_{\rm Z}\)-MIN & \(-0.051\) & \(-0.002\) & \(-0.079\) & \(-0.129\) & \(-0.053\) & \(0.081\) \\ diff\({}_{\rm Z}\)-MAX & \(0.122\) & \(0.184\) & \(0.165\) & \(0.245\) & \(0.042\) & \(0.453\) \\ diff\({}_{\rm Z}\)-MEAN & \(0.010\) & \(0.053\) & \(0.026\) & \(-0.002\) & \(-0.022\) & \(0.244\) \\ diff\({}_{\rm Z}\)-MEDIAN & \(0.013\) & \(0.048\) & \(0.019\) & \(-0.005\) & \(-0.022\) & \(0.237\) \\ diff\({}_{\rm Z}\)-SD & \(0.037\) & \(0.037\) & \(0.055\) & \(0.072\) & \(0.021\) & \(0.093\) \\ RMSE\({}_{\rm Z}\) & \(0.038\) & \(0.065\) & \(0.060\) & \(0.072\) & \(0.030\) & \(0.261\) \\ \hline \hline \end{tabular}
\begin{tabular}{c c c} \hline \hline diff\({}_{\rm Z}\)-MIN & \multicolumn{3}{c}{the minimum value of the differences in Z} \\ diff\({}_{\rm Z}\)-MAX & \multicolumn{3}{c}{the maximum value of the differences in Z} \\ diff\({}_{\rm Z}\)-MEAN & \multicolumn{3}{c}{the mean value of the differences in Z} \\ diff\({}_{\rm Z}\)-MEDIAN & \multicolumn{3}{c}{the median value of the differences in Z} \\ diff\({}_{\rm Z}\)-SD & \multicolumn{3}{c}{the standard deviation of the differences in Z} \\ RMSE\({}_{\rm Z}\) & \multicolumn{3}{c}{root mean square error of Z} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Basic statistics for differences in Z coordinate measured in the field by total station and obtained by the DSM_traditional or DSM_PPK.