# Testing Accuracy and Repeatability of UAV Blocks Oriented with GNSS-Supported Aerial Triangulation
## 4 Conclusions
The flights took place under good satellite constellations. Severe obstructions might be found flying in a high mountain environment, where dispensing with GCP is most important, and this might deteriorate the positioning quality. Future work will therefore focus on the influence of satellite configuration on the accuracy of camera projection centers. This study was supported by the Interreg V-A \"PrevRiskHauteMontagne\" project (No. 427), co-funded by the European Regional Development Fund, under the operational program for European Territorial Cooperation (ALCOTRA) France-Italy 2014-20. No funds have been received for covering the costs to publish in open access. **Author Contributions:** Experiment conception and design: [PERSON], [PERSON], [PERSON], and [PERSON]. Ground data acquisition: [PERSON], [PERSON], [PERSON], and [PERSON]. UAV flight planning: [PERSON], [PERSON], and [PERSON]. Imagery acquisition: [PERSON]. Data processing of UAV imagery: [PERSON], [PERSON], and [PERSON], [PERSON]. Manuscript drafting, analysis and interpretation of results: [PERSON], [PERSON], and [PERSON], [PERSON]. **Conflicts of Interest:** The authors declare no conflict of interest. The funding project had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**RTK+1 GCP**} & \multicolumn{4}{c}{**RTK+3 GCP**} \\ \hline  & \multicolumn{4}{c}{**RTK1**} & \multicolumn{4}{c}{} \\ \hline  & \multicolumn{4}{c}{**RTK1**} & \multicolumn{4}{c}{} \\ \hline
**Mean (m)** & 0.014 & 0.002 & 0.010 & \(-\)0.001 & \(-\)0.001 & \(-\)0.007 & \(-\)0.003 \\ \(\sigma\) **(m)** & 0.016 & 0.012 & 0.015 & 0.011 & 0.009 & 0.010 \\
**RMSE (m)** & 0.021 & 0.012 & 0.018 & 0.011 & 0.012 & 0.011 \\ \hline  & \multicolumn{4}{c}{**RTK2**} \\ \hline
**Mean (m)** & 0.014 & 0.006 & \(-\)0.002 & 0.009 & 0.001 & \(-\)0.002 \\ \(\sigma\) **(m)** & 0.009 & 0.011 & 0.021 & 0.008 & 0.009 & 0.019 \\
**RMSE (m)** & 0.017 & 0.013 & 0.021 & 0.012 & 0.009 & 0.019 \\ \hline  & \multicolumn{4}{c}{**RTK 3**} \\ \hline
**Mean (m)** & 0.002 & 0.009 & 0.024 & \(-\)0.002 & \(-\)0.002 & \(-\)0.011 \\ \(\sigma\) **(m)** & 0.015 & 0.012 & 0.032 & 0.014 & 0.006 & 0.027 \\
**RMSE (m)** & 0.015 & 0.015 & 0.039 & 0.014 & 0.006 & 0.029 \\ \hline  & \multicolumn{4}{c}{**RTK4**} \\ \hline
**Mean (m)** & 0.007 & 0.002 & \(-\)0.011 & 0.004 & \(-\)0.009 & 0.007 \\ \(\sigma\) **(m)** & 0.025 & 0.012 & 0.027 & 0.022 & 0.009 & 0.029 \\
**RMSE (m)** & 0.026 & 0.012 & 0.029 & 0.022 & 0.013 & 0.030 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Statistics of the residuals in X, Y and \(Z\) coordinate on 13 checkpoints for the two BBA configurations: **RTK+1 GCP** and **RTK+3 GCP**. Figure 11 Plot of RMSE in elevation obtained with PhotoScan for RTK1 and RTK3 with PhotoScan. The arrows depict the magnitude and direction of the horizontal coordinate changes; the diameter of the circles represents the magnitude of the elevation change, in blue and red colors, respectively, for positive and negative variations.