Abstract
Inertial sensors offer the potential for integration into wireless virtual reality systems that allow the users to walk freely through virtual environments. However, owing to drift errors, inertial sensors cannot accurately estimate head and body orientations in the long run, and when walking indoors, this error cannot be corrected by magnetometers, due to the magnetic field distortion created by ferromagnetic materials present in buildings. This paper proposes a technique, called EHBD (Equalization of Head and Body Directions), to address this problem using two head- and shoulder-located magnetometers. Due to their proximity, their distortions are assumed to be similar and the magnetometer measurements are used to detect when the user is looking straight forward. Then, the system corrects the discrepancies between the estimated directions of the head and the shoulder, which are provided by gyroscopes and consequently are affected by drift errors. An experiment is conducted to evaluate the performance of this technique in two tasks (navigation and navigation plus exploration) and using two different locomotion techniques: (1) gaze-directed mode (GD) in which the walking direction is forced to be the same as the head direction, and (2) decoupled direction mode (DD) in which the walking direction can be different from the viewing direction. The obtained results show that both locomotion modes show similar matching of the target path during the navigation task, while DD’s path matches the target path more closely than GD in the navigation plus exploration task. These results validate the EHBD technique especially when allowing different walking and viewing directions in the navigation plus exploration tasks, as expected. While the proposed method does not reach the accuracy of optical tracking (ideal case), it is an acceptable and satisfactory solution for users and is much more compact, portable and economical.
Highlights
In 1965, Ivan Sutherland presented the concept of The Ultimate Display [1] system that would control the existence of matter in a way that, for example, would allow us to take a seat in a virtual chair
In the remainder of this paper, the natural locomotion virtual reality system we have developed together with the technique proposed for addressing the drift errors in yaw angle are described in the Materials and methods section, which provides a detailed description of the conducted experiments
The analysis showed that the deviation from the ideal path during the navigation task (NAV) task does not differ significantly between the direction mode (DD) and gaze-directed mode (GD) groups (Fig 10)
Summary
In 1965, Ivan Sutherland presented the concept of The Ultimate Display [1] system that would control the existence of matter in a way that, for example, would allow us to take a seat in a virtual chair. Natural locomotion attempts to approximate real-world walking and brings important benefits to virtual reality systems such as better proprioceptive cues, enhanced distance judgment and increased sense of presence [2]. Examples include flat treadmills [3,4,5]; spherical treadmills [6]; robotic tiles [7]; robotic actuators [8,9]; motorized skates [10]; and sliding disks [11,12,13] These systems are able to let the user walk in a natural way while they are confined within a restricted space (walking in place systems). A small area can be useful and sufficient for the development of a number of applications
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