## 7 Results and Discussion  
### Laser Scanning  
#### 7.1.1 Amezzrou Synagogue  
A small object (interior of synagogue in Amezrou) was documented by both scanners, using photogrammetry too, so it was possible to define the mutual accuracy and work efficiency (Table 3). By working with BLK360, only four scanner position were used, located approximately in the corners. The measurement took approximately 30 min. All four scans were processed after expedition in Cyclone 360 Register software. Joining of collected scans was a fully automated process based on correlation as \"cloud-to-cloud\" process. Finally, a report was prepared, which showed accuracy characteristics (Table 4). Six links were found between four scanner stations. The final joined point cloud, created from BLK360, was set as a reference measurement because this scanner produces relatively precise measurement on short distances, in this case, 3-4 millimetres in measured distances. Measurement with the ZEB-REVO scanner was very fast and simple (Figure 20). Since no geodetic control points were used to test the accuracy, the joined point cloud from the BLK360 scanner, which has an order of magnitude higher accuracy, was used to compare the accuracy of this new PLS device. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Link Nr.** & **Combination** & **Overlap [\%]** & **Abs. Mean Error [m]** \\ \hline Link 1 & 1–2 & 63 & 0.004 \\ Link 2 & 1–3 & 65 & 0.003 \\ Link 3 & 1–4 & 95 & 0.003 \\ Link 4 & 2–3 & 93 & 0.003 \\ Link 5 & 2–4 & 63 & 0.004 \\ Link 6 & 3–4 & 63 & 0.003 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results from the BLK360 laser scanner, the synagogue in the Amezrou. Figure 19: The village of Mansouria. (**a**) An original plan after an automated vectorization from GeoSlam Draw, Mansouria (Zagora); (**b**) an edited vector plan from GeoSlam Draw (approximately four hours of editing of the original automated vectorizing). Close-range photogrammetry was used only in addition. Due to lack of time and poor lighting condition, only a mobile phone camera was used. All the data were processed at the university post-expedition. From laser scanners, point clouds were computed and exported to the CloudCompare software (Figure 21) As a reference point cloud, the BLK360 measurement were selected, because it was complex and most accurate from all three methods. Differences after automatically joining of four measured point clouds reaches only 3 mm and 4 mm, respectively, with average overlap more than 80% based on the computational report (Table 4). This final point cloud from BLK360 was compared with the point cloud created by ZEB-REVO PLS. It is visible here (Figure 21) that absolute differences between both point clouds are under 2 cm, typically 1 cm only. A visible difference is only on the left (somebody  
Figure 21: Comparison of joined point clouds from both laser scanners in CloudCompare (CC) software. Figure 20: Graphical output from the ZEB-REVO PLS: The ground plan of structures inside the _mellah_ (in red colour the trajectory during measuring). This output can be produced in dozens of minutes. has opened the doors), on the top (the tips of the triangle are not visible in BLK360 point cloud), and right (our relocated backpacks). Further accuracy comparisons were made on cross-sections (Figure 22). The variance of data noise and point density manifested itself here. It can be seen in Figures 22 and 23 that due to unsuitable conditions, the point cloud from close-range photogrammetry contains considerable noise and errors (green dots, variance up to several cm). The point cloud from the BLK360 scanner is accurate and contains very little data noise (variance is only within 2-5 mm). The data from the ZEB-REVO scanner are sparse when compared to the two named outputs and has significant variance in points, typically 1-2 cm.