Outdoor virtual reality (VR) places users in dynamic physical environments where they must remain aware of real-world obstacles, including static structures and moving bystanders, while immersed in a virtual scene. This dual demand introduces challenges for both user safety and presence. Millimeter-wave (mmWave) radar offers a privacy-preserving alternative to camera-based sensing by detecting obstacles without capturing identifiable visual imagery, yet effective methods for communicating its sparse spatial information to users remain underexplored. In this work, we developed and validated WaveWalkerClone, a reproduction of the WaveWalker system, to establish reliable radar- and GPS-IMU-based sensing under varied outdoor lighting conditions. Building on this feasibility validation, we conducted a user study (n=18) comparing three visualization techniques for radar-detected obstacles : (1) diegetic alien avatars that visually embed obstacles within the virtual narrative, (2) non-diegetic human avatars represented obstacles as humans inconsistent with the virtual narrative, and (3) abstract point clouds centered around the obstacles conveying spatial data without anthropomorphic or narrative associations. Our results show that all three approaches supported user safety and situational awareness, but yielded distinct trade-offs in perceived effort, frustration, and user preference. Qualitative feedback further revealed divergent user responses across conditions, highlighting the limitations of a one-size-fits-all approach. We conclude with design considerations for obstacle visualization in outdoor VR systems that seek to balance immersion, safety, and bystander privacy.

翻译：户外虚拟现实（VR）将用户置于动态的物理环境中，要求其在沉浸于虚拟场景的同时保持对现实世界障碍物（包括静态结构与移动行人）的感知。这种双重需求给用户安全与临场感带来了挑战。毫米波雷达通过探测障碍物且不捕获可识别视觉图像，提供了基于摄像头传感的隐私保护替代方案，然而将其稀疏空间信息有效传达给用户的方法仍有待探索。本研究开发并验证了WaveWalkerClone（WaveWalker系统的复现版本），以在多变户外光照条件下建立基于雷达与GPS-IMU的可靠传感。基于此可行性验证，我们开展了用户研究（n=18），比较三种雷达探测障碍物的可视化技术：（1）叙事性异形化身——将障碍物视觉化嵌入虚拟叙事中；（2）非叙事性人类化身——以与虚拟叙事不符的人类形象表征障碍物；（3）以障碍物为中心的抽象点云——传达空间数据而不赋予拟人或叙事关联。研究结果表明，三种方法均能支持用户安全与情境感知，但在感知努力度、挫败感及用户偏好方面产生明显权衡。定性反馈进一步揭示了不同条件下用户的差异化反应，凸显了通用化方案的局限性。最后，我们为户外VR系统提出平衡沉浸感、安全性与行人隐私的障碍物可视化设计考量。