## 3 Results
### Experiment (4): GNSS Master Station  
The fourth experiment based on the single strip measurements data set is investigating the impact of different GNSS master stations on the quality of the georeferenced point cloud. In addition to the own master station mounted on a pillar and used for all experiments before, a CORS station and two different VRS are used within the processing. The evaluation parameters are identical to **Experiment (2)** based on the difference of target center coordinates compared to the TLS reference and the corresponding RMSE of targets centers from four flight repetitions. The calculated differences are shown in Figure 11 for the four different master stations each for the coordinate difference in the east (blue), north (red) and height (yellow) direction.  
In addition, the mean absolute difference is indicated in each histogram and in combination with the RMSE given in Table 5. The parameters are estimated based on eight  
Figure 11: Difference of the estimated target coordinates compared to the TLS reference when using different master stations for the trajectory estimation. In addition to the own master station used before, a CORS station and two VRS are used. The histograms show the combined results for four flights and all targets included considering the east (blue), north (red) and height (yellow) coordinates.  
Figure 10: Tilt of planes estimated from UAV point cloud compared to the TLS reference in flight and across flight direction.  
targets for each of the four flights which leads to a total number of 32 targets used for the computation.  
In the visual evaluation with Figure 11, the results for the estimated coordinates for different master stations are very similar without much variation. This is stated also with the calculated mean difference as quantification of the absolute accuracy, which only differs in the mm range between different solutions. The expectation beforehand for absolute accuracy was, that results based on own master station would perform best since the pillar coordinates are well known and the conditions for GNSS observations are the same as for the UAV. Comparing the mean difference of the own master station with both VRS and the CORS station, the difference is slightly higher and the results for the RMSE can be rated as equal. Summarizing the absolute accuracy for the comparison of different GNSS master stations, the results are equal on the cm level. The estimated offset is about 1 cm in the horizontal direction and about 3 cm in the vertical direction for all variations of processing. Additionally, the RMSE is used as a measure of the quality, where results are similar or even identical for different master stations. In this case, the own master station provides the best results but without a substantial deviation from the other ones. The conclusion from the evaluation of the **Experiment (4)** leads to the statement that the use of a VRS and also a CORS station in 16 km distance delivers similar results. Since setting up an own master station always involves additional effort, the two other variants offer a viable alternative that can be recommended. In particular, the use of a VRS is a frequently used approach anyway and is probably the best variant for many applications.