## 3 Results  
### Assessing the Accuracy of Bundle Block Adjustment  
Table 3 shows the several statistics computed to assess the accuracies of BBA_traditional and BBA_PPK. On the average, the BBA_traditional presented the smallest minimum value of the differences per coordinate. The differences range from \(-\)0.098 m (Krnica, diff\({}_{\rm{X}}\)) to 0.091 m (Krnica, diff\({}_{\rm{Y}}\)) in the case of BBA_traditional, while the differences with BBA_PPK were higher; they range from \(-\)0.171 m (Mangart, diff\({}_{\rm{Y}}\)) to 0.431 m (Mangart, diff\({}_{\rm{Z}}\)). The mean value of differences ranges from \(-\)0.006 m (Kekec, diff\({}_{\rm{Y}}\)) to 0.009 m (Kekec, diff\({}_{\rm{Z}}\)) in the case of BBA_traditional. The mean value of the differences with BBA_PPK were higher, and range from \(-\)0.109 m (Mangart, diff\({}_{\rm{Y}}\)) to 0.245 m (Mangart, diff\({}_{\rm{Z}}\)). The standard deviations of the differences were similar for both BBA methods for all coordinates when observing the Kekec (from 0.008 to 0.010 m) and Krnica site (from 0.014 to 0.031 m). At Mangart site, the BBA_PPK had larger standard deviations than BBA_traditional, namely reaching 0.028 for diff\({}_{\rm{X}}\), 0.047 m for diff\({}_{\rm{Y}}\), and 0.092 m for diff\({}_{\rm{Z}}\), while BBA_traditional had values between 0.007 and 0.008 m.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Units in m**} & \multicolumn{2}{c}{**KEkEC**} & \multicolumn{2}{c}{**KRNICA**} & \multicolumn{2}{c}{**MANGART**} \\ \cline{2-7}  & **BBA\_Traditional** & **BBA\_PPK** & **BBA\_Traditional** & **BBA\_PPK** & **BBA\_Traditional** & **BBA\_PPK** \\ \hline diff\({}_{\rm{X}}\)-MN & \(-\)0.017 & \(-\)0.001 & \(-\)0.098 & \(-\)0.091 & \(-\)0.029 & \(-\)0.148 \\ diff\({}_{\rm{X}}\)-MAX & 0.020 & 0.037 & 0.056 & 0.057 & 0.011 & \(-\)0.043 \\ diff\({}_{\rm{X}}\)-MEAN & 0.004 & 0.017 & 0.001 & 0.013 & \(-\)0.004 & \(-\)0.098 \\ diff\({}_{\rm{X}}\)-MEDIAN & 0.004 & 0.016 & 0.004 & 0.015 & \(-\)0.003 & \(-\)0.100 \\ diff\({}_{\rm{X}}\)-SD & 0.008 & 0.009 & 0.026 & 0.029 & 0.008 & 0.028 \\ RMSE\({}_{\rm{X}}\) & 0.009 & 0.019 The lowest RMSE values per coordinate were achieved with the BBA_traditional method at the Kekec and Mangart study sites, with the RMSE values lower than 0.015 m in all coordinates (Kekec, RMSE\({}_{\text{X}}\) = 0.009 m, RMSE\({}_{\text{Y}}\) = 0.010 m, and RMSE\({}_{Z}\) = 0.014 m; Mangart, RMSE\({}_{\text{X}}\) = 0.009 m, RMSE\({}_{\text{Y}}\) = 0.008 m, and RMSE\({}_{Z}\) = 0.007 m). At the Krnica study site, the results were slightly worse, but the RMSE in all coordinates did not exceed 0.029 m (Krnica, RMSE\({}_{\text{X}}\) = 0.026 m, RMSE\({}_{\text{Y}}\) = 0.020 m, and RMSE\({}_{Z}\) = 0.015 m). The RMSE values per coordinate with the BBA_PPK method ranges from 0.019 to 0.050 m at the Kekec and Krnica rockfall site, while at the Mangart rockfall site, RMSE values per coordinate achieve values between 0.102 and 0.261 m.  
The overall accuracy of BBA (RMSE\({}_{\text{XYZ}}\)) was higher in the case of BBA_traditional (range from 0.014 to 0.036 m); namely, in the case of the BBA_PPK method, the RMSE\({}_{\text{XYZ}}\) ranged from 0.056 to 0.305 m. Figure 6 shows the frequency distributions of the diff\({}_{\text{X}}\), diff\({}_{\text{Y}}\), and diff\({}_{Z}\) at the sites for both georeferencing methods. It can be observed that the differences related to BBA_traditional method are closely clustered around 0, having uni-modal distribution. The differences related to the BBA_traditional coincided with BBA_PPK, with the latter having a larger span of values, with the exception of the Mangart location, where the differences of BBA_traditional and BBA_PPK coincided in a small part or not at all. A paired Student's \(t\)-test, for testing whether there was a statistically significance difference in the mean value of differences between the BBA_traditional and BBA_PPK, was used in three cases: diff\({}_{\text{X}}\), diff\({}_{\text{Y}}\), and diff\({}_{Z}\) in Mangart.