# An Aerial Mixed-Reality Environment for First-Person-View Drone Flying
## 4 Experimental Results
### Actual Flight Experiences  
As a formative assessment, the second user study examined the effectiveness of the proposed MR environment. To investigate the differences in FPV flights when actual users controlled the drone in the real word, and VR and MR environments, four drone pilots (average age: 32.75 years; range: 25-36 years) were recruited to perform a qualitative user study. Two of these were expert pilots belonging to the FPV racing drone community, whereas the other two were experienced in FPV drone flights. Experts skilled in drone control were recruited for this user study because they were required to compare this MR system with the actual FPV drone system. Furthermore, they were required to skillfully play 3D video drone games using a VR HMD. Therefore, the group that satisfied this condition was small. In the experiment, all participants did not experience simulator sickness. Figure 11 shows a user controlling a drone using the proposed MR system and their viewpoints. To compare the immersion in controlling the drone in each environment, we conducted a qualitative user study after a real FPV drone flight, an MR-based FPV drone flight, and a manipulation of a virtual FPV drone in the virtual simulator AirSim by expert pilots. Figure 7 shows the images recorded during this experiment. The flight in the proposed MR environment had a wider viewing angle and higher resolution than the real FPV drone flight. Furthermore, the camera mounted in the proposed MR drone was a stereo camera, which provided a greater stereoscopic sense than the images received from the drone with a mono camera. Finally, the differences in the generated virtual obstacles were compared with real obstacles. All of the participants were skilled drone pilots with experience playing 3D video games using a VR HMD. However, two of the drone pilots had only previously manipulated third-person-view drones and participated in the experiment after becoming familiar with FPV drone flights through several practices. The drone experts performed flight in an MR environment after completing flights in a real FPV drone and those in a VR environment. Tables 2 and 3 list the differences between the environments. Compared with the real FPV drone flight, the positive differences of the proposed MR environment are wide viewing angle, high resolution, strong sense of depth, and no adaptation time required. The participants reported that the concentration of manipulation increased as the viewing angle widened during flight. When flying a real FPV drone, they must become acquainted with the flight path before starting a flight owing to the limited viewing angle because the current moving direction cannot be determined easily based on the limited viewing angle. This is consistent with the research results of [PERSON] et al. [53] and [PERSON] et al. [54], i.e., when the viewing angle widens, the pilot can concentrate on understanding the space because the distraction of spatial understanding and spatial memory is reduced. Like real obstacles, all participants felt the presence of virtual objects created by the MR system. However, they reported slight simulator sickness because virtual 3D objects were generated, particularly when a crash with virtual objects occurred. The weak simulator sickness felt  
Figure 10: The average score of immersion and standard deviation for experience in each environment. in this case may be attributed to two factors. The first is that the sense of reality collapsed because the obstacles passed without the drone falling or shaking, which may occur because of collision with objects. The second possible factor is that extreme differences occurred in the images rendered in both eyes because only one of the two eyes of the stereo camera overlapped with the inside of the virtual objects. Expert pilots reported that appropriate effects during a collision with virtual objects may help alleviate simulator sickness.