# An Aerial Mixed-Reality Environment for First-Person-View Drone Flying
## 4 Experimental Results
### Immersion in FPV Flights  
To evaluate the usability of the proposed MR-based FPV flight, its flying experience was compared with that of a drone flight simulator. For this comparison, 16 participants (average age: 25.44 years; range: 22-31 years) wore a VR HMD and viewed flying scenes controlled by an experienced drone pilot in each environment. The experience of VR simulators is generally evaluated by active task completion. However, in the first user study, we compared the cinematic VR experiences in both environments so that differences were not caused by the operation difficulty between a real FPV drone and a simulator. These experiences are passive, but the viewer is still engaging in multiple cognitive activities. The evaluation techniques for cinematic VR experiences were proposed by [PERSON] et al. [50] and a similar evaluation approach to ours was used in [51]. Figure 9 shows the flying scenes of each environment and a participant in the indoor experiment. The top images are the viewpoint of the drone flying in a virtual environment, which was created similarly to the experimental environment shown in Figure 8 by modifying a virtual space provided by Microsoft AirSim, a popular drone flight simulator. The bottom images are the view of the pilot flying in our MR environment. The flying scenes from a stereo camera were recorded for 1 min in the same experimental environment. The drone pilot flew at a speed below 4 m/s to the destination in each environment without hitting the obstacles. In both environments, a viewing angle of \(110^{\circ}\) and a resolution of \(2160\times 1200\) were used. All participants were experienced in playing 3D video games using a VR HMD, and no participant felt strong motion sickness during the experiment. The participants engaged in the experiment for up to 20 min including the warm-up time, and they experienced drone flights at a stable speed below 4 m/s because a higher drone speed could induce simulator sickness [41]. Subsequently, the participants responded to the questionnaire shown in Table 1 such that the overall user immersion after experiencing each environment could be measured. The simplified questionnaire for measuring immersion [39] comprised 24 questions. The 18 questions for measuring immersion in the configuration of each  
Figure 8: An experimental drone racing environment in a drone airfield. Figure 9: A participant viewing FPV flying scenes in virtual reality (VR) and MR environments. environment could be answered based on a five-point agreement scale. They comprised four questions regarding emotion, three regarding flow, three regarding immersion, three regarding judgment, and five regarding presence. Furthermore, because the degree of simulator sickness [52] affects the user's immersion, six questions regarding the experience were posed to determine it. The replies to positive questions were marked as \"P\" and negative ones as \"N\". The reactions of each participant were analyzed by calculating the scores of their replies to each question. In this questionnaire, scores on a five-point Likert scale were calculated (strongly agree = 5, agree = 4, average = 3, disagree = 2, and strongly disagree = 1). For negative questions, the scores were set in the opposite order. Significant results were obtained from the negative and positive reactions. The response of all participants to each question was calculated using the average score. Figure 10 shows the average score and standard deviation of immersion (including 18 questions for measuring immersion and six questions for simulator sickness affecting the immersion) according to the experience level of each environment. Both environments showed positive results for immersion, with 3 points (average immersion) or higher. Furthermore, the flight in the MR environment showed an overall immersion that was higher by approximately 0.41 than the flight in the VR environment.