## 4 Experiment  
### Experimental Design  
We aimed to utilize virtual reality to simulate outdoor mixed-reality navigation through mobile head-mounted displays, such as HoloLens [59], in real-world scenarios. To better control irrelevant variables in the experiment and to face the risk of outdoor activity resulting from COVID-19, in this work, we planned to use a virtual reality environment to simulate a mixed-reality scenario to conduct a user study. Moreover, the research on mixed-reality 3D minimap design for exploratory navigation is not rich in the literature, and we expect this study will become an inspiration for further study as well. The design of 3D minimap in this work is still in the preliminary stage, so we could make use of the advantages of virtual reality, such as lower cost, variation control, and easier manipulation to conduct the user study for mixed-reality applications, and we conducted a field study in the real world after studies in simulation. Utilizing the virtual reality method to simulate augmented reality and mixed-reality study is common in research [60; 61; 62; 63]. The advantage of this method is reducing the cost of outdoor field experiments, and since it is easier to recognize the problems that the design should overcome during testing, it is worth experiencing the augmented reality and mixed-reality prototype after virtual reality [64; 65]. Figure 6 shows the design concept for participants in the virtual scene with a 3D minimap. We implemented a virtual urban scene and used a virtual reality head-mounted display to simulate the mixed-reality features. To discuss the exploratory navigation comprehensively, we designed two experimental tasks described in Figure 7. We designed the exploration task and navigation task to simulate the activities in urban exploratory navigation. After each task, the answers to the questionnaires and interviews were recorded. The virtual urban scene was implemented in Unity 3D [66]. We used the open prefab models imported from the Unity Asset Store to implement the Senso-Ji in Tokyo as a virtual urban street environment, as illustrated in Figure 8. We included detailed buildings, landmarks, streets, plants, facilities, and other environmental information. We used Oculus Quest 2 [67] to simulate the mixed-reality scenario outdoors. Figure 5: (**Left**): normal mixed-reality 3D minimap design; (**Right**): simplified mixed-reality 3D minimap design. In the exploration task, we aimed to measure the performance in terms of the collected points of interest, perceived workload, and user experience in the two map modes. The participant was asked to explore an urban street area. We set a series of points of interest in the virtual scene and marked these points of interest in the minimap interface as well. The participants were asked to explore and arrive at these points of interest in the virtual scene according to the minimap. This task aimed to simulate exploration activities such as check-in behavior in a tourism destination. In another task, the participant needed to utilize the virtual minimap for orientation and navigation to collect stars within a session. We also implemented a scoring system to record the number of collected points of interest. The  
Figure 6: Implementation description. Figure 7: Experimental design. starting points and the series of marked point-of-interest locations in the two map modes were designed differently to avoid an influence on the latter experiment resulting from the former one. We measured the number of collected points-of-interest as quantitative data, and we used the subjective questionnaire NASA-TLX [34] and game user experience questionnaire [68] as qualitative data for later analysis and discussion. In the navigation task, we aimed to measure the navigation efficiency (navigation time(s)), perceived workload, and user experience in the two map modes.