## 4 Conclusions and Outlook  
This paper presents an evaluation strategy for the quality assessment of single measurements with a UAV-based laser scanning system and, in particular, the capability for direct georeferencing and the corresponding absolute accuracy and precision. Since the evaluation of a UAV-based laser scanning system is non-trivial due to the complex processing chain and included error sources, the evaluation is performed on the derived point cloud using parameter-based and point-based evaluation strategies. The first study area was designed similar to the challenges within corridor mapping. With this flight planning, systematic errors due to trajectory estimation and especially system calibration are detectable. With the use of a second study area and the different flight plan based on a cross-flight pattern, the capability of RIEGL's software RiPRECISION was analyzed. The comparison for both study areas is performed with a TLS point cloud reference and the use of different objects like tables and targets. The following results are structured in the same order as the research aspects in Section 2.2 and summarize the results from both study areas. 1. The first parameter describing the noise and therefore the range precision of the laser scanner resulted in \(0.4\) cm for the flight height of \(10\) m for the single strip measurements and \(0.6\) cm for the flight height of \(25\) m for the multiple strip measurements. With the second data set, the performance of RiPRECISION is evaluated as well, which performs a proper alignment of several strips from the cross-flight pattern. Figure 13: Tilt of planes estimated from UAV point cloud compared to the TLS reference in north and east direction. 2. The absolute accuracy using the target-based evaluation for four separated flights was given with 0.9 cm in east, 1.9 cm in north and 3.4 cm in height direction for the single strip measurements. The additional focus to the vertical direction using table heights provided nearly the identical height offset of 3.4 cm with a RMSE of 1.3 cm. The results for the multiple strip measurements are consistent with everything concluded from the first data set with a mean difference in the horizontal direction around 1 cm and in vertical direction around 4 cm. The additional parameter-based evaluation was performed for the two different study areas and the tilts between estimated planes are always within the noise level of the point cloud and no systematic effects are observed. 3. The precision of the UAV system resulted in a standard deviation of 0.7 cm for the east, 1.1 cm for the north and 1.2 cm for height direction. The system provides excellent results over the whole study area for the single strip measurements. The same analysis resulted in a precision of 0.8 cm in the east, 0.5 cm in the north and 2.1 cm in height direction for the multiple strip measurements. 4. The impact of different master stations is assessed by the use of an own master station, a CORS station and two different VRS. The output of the performed point-based evaluation leads to nearly identical results for the four different GNSS data sets and therefore the conclusion, that strategy should be chosen, which is easiest to handle for the user. Overall, the VRS and the CORS station have shown good results considering the mean absolute difference and are therefore an appropriate alternative for the processing. Besides the investigations of absolute accuracy, this study shows a new investigation approach for analyzing the precision of UAV-based laser scanning systems. By the use of identical flight planning and repeated measurements, the independent data sets are usable for a precision investigation. This approach can also be performed on a larger scale with different flight parameters and the use of natural objects for similar quality analysis. Overall, the results for the used UAV-based laser scanning system are better than expected based on the manufacturer's specification.