Immersiveness is the main characteristic of Virtual Reality(VR) applications. Precise integration between hardware design and software are necessary for providing a seamless virtual experience. Allowing the user to navigate the VR scene using locomotion techniques is crucial for making such experiences `immersive'. Locomotion in VR acts as a motion tracking unit for the user and simulates their movement in the virtual scene. These movements are commonly rotational, axial or translational based on the Degree-of-Freedom (DOF) of the application. To support effective locomotion, one of the primary challenges for VR practitioners is to transform their hardware from 3-DOF to 6-DOF or vice versa. We conducted a systematic review on different motion tracking methods employed in the Head-Mounted-Devices (HMD) to understand such hardware transformation. Our review discusses the fundamental aspects of the hardware-based transformation of HMDs to conduct virtual locomotion. Our observations led us to formulate a taxonomy of the tracking methods based on system design, which can eventually be used for the hardware transformation of HMDs. Our study also captures different metrics that VR practitioners use to evaluate the hardware based on the context, performance, and significance of its usage.

翻译：沉浸感是虚拟现实（VR）应用的主要特征。硬件设计与软件之间的精确集成对于提供无缝的虚拟体验至关重要。允许用户通过运动导航技术探索VR场景是实现这种"沉浸感"的关键。VR中的运动导航作为用户的运动追踪单元，可模拟其在虚拟场景中的移动。这些移动通常基于应用的自由度（DOF）表现为旋转、轴向或平移运动。为支持高效运动导航，VR从业者面临的核心挑战之一是将硬件从3-DOF转换为6-DOF，或反之亦然。我们对头戴式设备（HMD）中采用的多种运动追踪方法进行了系统综述，以理解此类硬件变换。本综述讨论了基于硬件的HMD变换以实现虚拟运动导航的基本原理。基于观察，我们构建了基于系统设计的追踪方法分类体系，该体系最终可用于HMD的硬件变换。本研究还梳理了VR从业者根据使用场景、性能及重要程度评估硬件时采用的不同指标。