# Integrating a LiDAR Sensor in a UAV Platform to Obtain a Georeferenced Point Cloud
## 3 Results
#### Procedure Validation  
In Figure 19, the control points used for validating the procedure are indicated in orthophoto (Figure 19a) and plan (Figure 19b) formats. Table 6 lists the coordinates obtained using the different survey methods (total station, LiDAR and photogrammetry). In contrast, Table 7 lists the coordinate comparison errors between the reference control points obtained with the total station and the control points obtained with the LiDAR and photogrammetry procedures. These errors mainly reflect the positional error between the GPS and the differential GPS of the UAV. Figure 19: Control points for validation. (**a**) Area points in orthophoto; (**b**) Area points in plan. Figure 18: Point cloud display in the LiDAR 360 software, after removing outliers and filtering noise. Colors indicate the height range of the collected volumes. As a first result, a root mean square error (RMSE) of 35.514 m was obtained from georeferencing (Table 7). In the sequence, as part of the process, an offset for the georeferencing errors from the survey is added into the workflow, in which the LiDAR point cloud is superimposed on the previously defined coordinates from the total station. For this application case, the translation values were 1.757 m along the \(X\)-axis and 1.867 m along the \(Y\)-axis at point T4. In addition, two reference points are located for the survey overlay. In this example, the turn was 55\({}^{\circ}\), as shown in Figure 20.  
In Figure 21, the same processing was applied for the translation along the \(Z\) axis. For this case, the value was 35 m. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Flight Parameters**} \\ \hline Flight Lines & 5 \\ Altitude & 40 m \\ Flight Time & 3 min \\ Flying Speed & 3.6 m/s \\ Cover Area & 0.44 Ha \\ Front Overlap & 81\% \\ Side Overlap & 87\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Flight parameters. Figure 20: LiDAR point correction for the \(X\) and \(Y\) axes. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{6}{c}{**Total Station (Reference)**} & \multicolumn{3}{c}{**LiDAR**} & \multicolumn{3}{c}{**Photogrammetry**} \\ \hline
**Point** & **x** & **y** & **z** & **x** & **y** & **z** & **x** & **y** & **z** \\ \hline T1 & 8,663,213.326 & 285,605.3695 & 255,153 & 8,663,211.895 & 285,608.022 & 219,431 & 8,663,213.268 & 285,605.359 & 255,333 \\ T2 & 8,663,206.688 & 285,612.849 & 256,828 & 8,663,205.159 & 285,615.639 & 221,326 & 8,663,206.696 & 285,612.849 & 256,849 \\ T3 & 8,663,200.097 & 285,620.306 & 255,22 & 8,663,198.054 & 285,622.75 & 219,698 & 8,663,200.119 & 285,620.300 & 255,265 \\ T4 & 8,663,151.505 & 285,577.635 & 255,265 & 8,663,149.748 & 285,579.502 & 220,149 & 8,663,151.5 & 285,577.631 & 255,188 \\ T5 & 8,663,158.034 & 285,570.161 & 256,765 & 8,663,156.595 & 285,572.131 & 221,608 & 8,663,158.031 & 285,570.151 & 256,738 \\ T6 & 8,663,164.644 & 285,562.647 & 255,252 & 8,663,163.092 & 285,564.911 & 219.89 & 8,663,164.641 & 285,562.663 & 255,434 \\ \hline \end{tabular}
\end{table} 
Table 7: Coordinates of the surveyed points obtained with a total station, LiDAR and photogrammetry. The results from this procedure are described in Tables 8 and 9. The corrected control points are shown according to the section and the related equipment (Table 8). Table 9 denotes the RMSE for the LiDAR survey obtained through georeferencing, whose value is 0.766 m concerning the total station. of LiDAR also found that the Z-axis presents the most errors in trials done with the system, sometimes exceeding that manufacturer's information [36; 37]. Table 10 shows the corrected control point cloud errors and Table 11 compares the values from measuring the distances between the control points with LiDAR and UAV photogrammetry and the reference points from the total station (TS) to determine the accuracy of the measurements of the lifted objects. Here, the maximum absolute error between the LiDAR and the TS was 0.347 m between points T3 and T4, and the absolute minimum error was 0.10 m between T1 and T2.