# Testing Procedure of Unmanned Aerial Vehicles (UAVs) Trajectory in Automatic Missions
## 4 Discussion

Table 11: Values of distances to the ends of mission flight lines (maximum, minimum, their ranges, mean values, and standard deviations) for data in task 5.  
measurements, it should be noted that, for long-term hovering of the UAVs that were equipped with this type of on-board computers, the vertical drift should be taken into consideration. It will not be visible in the telemetry data that are transmitted from the UAV to the control station. The value of the drift determined on the data captured from the MS50 surveying instrument in all tests has had a value that indicates the lowering of the flying altitude. The resulting lack of proper separation of the UAVs from obstacles is extremely dangerous, especially in automated missions. This effect could be very dangerous in urban environments, e.g., when UAV is flying close to infrastructure or during flights at low altitudes [31; 33; 37; 66]. In the case of short-term hovering of the device in order to take single photographs or film shots, the negative impact of the barometric sensor drift is of no importance. In the case of the obtained results, the implementation of the ISO standards for industrial robots [42; 43; 59; 60] is not justified due to the differences in the positioning accuracy of the device in the horizontal and vertical planes, Tables 3-5. It is required to carry out the accuracy test for the systems that are responsible for separately maintaining the horizontal and vertical positions. Comparison between Euclidean distance estimations in paper [47; 48] is justified by the characteristics of the tested devices on small test fields. Moreover, the extension of this test set should be considered, taking into account the autonomy levels that were proposed in [23; 68]. In this paper, the tests have included the devices with a first degree of autonomy. This set of tests will also allow the verification of the efficiency of the parameters of the EKF [65], as a control tool to examine pre-programmed on-board computer. Taking into account the results that were obtained in tasks 4 and 5, the author has carried out the analysis of the influence of inaccuracy on the implementation of photogrammetric missions on the image overlap. The UAV flight that was performed in the horizontal plane, inconsistently with the design, results in a reduction or increase in the distance between successive flight lines, Figures 8 and 10. This will result in a reduction or increase in side overlaps between the adjacent flight lines. The recorded maximum differences between the designed distances and the implemented ones reached 5.00 m. For the analysis to be as legible as possible, Table 12 compares the changes of side overlaps for the images with different widths, with the distances between the lines changing by 2.50; 5.00; and, 10.00 m. The table only presents the situations where the distance between the lines has increased in relation to the design, resulting in the reduced side overlap of the images. The 60% side overlap, recommended by most manufacturers of data processing software, has been used as the initial value [12; 69; 70]. The size of the GSD (ground sampling distance), the focal length, and the size of the matrix have been rendered irrelevant for this analysis. In the further part of the discussion, it has been assumed that the change in the coverage to the value of 55% is insignificant. It is worth noting that, for images with a width of 40 m, the alterations in distance between the lines even as small as 2.50 m, change the value of the side overlap to 53.8%. In addition, Table 12 demonstrates the combinations of image sizes and differences in the distances between the lines, which have resulted in the changes in coverage to less than 50%. For the images with widths exceeding 200 m, the changes in the side overlap, due to incorrect implementation of the mission, result in a reduction of the coverage to a minimum of 55.0%.