Outstanding: a Multi-Perspective Travel Approach for Virtual Reality Games

Outstanding: A Multi-Perspective Travel Approach for Virtual Reality Games Sebastian Cmentowski, Andrey Krekhov, Jens Krüger High Performance Computing Group University of Duisburg-Essen, Germany {sebastian.cmentowski, andrey.krekhov, jens.krueger}@uni-due.de Figure 1. Our proposed navigation technique allows players to switch to a scaled third-person perspective on demand and control a virtual avatar to cover large distances in open world VR scenarios. ABSTRACT demand. From above, players can command their avatar and In virtual reality games, players dive into fictional environ- initiate travels over large distance. Our evaluation reveals a ments and can experience a compelling and immersive world. significant increase in spatial orientation while avoiding cyber- State-of-the-art VR systems allow for natural and intuitive nav- sickness and preserving presence, enjoyment, and competence. igation through physical walking. However, the tracking space We summarize our findings in a set of comprehensive design is still limited, and viable alternatives are required to reach fur- guidelines to help developers integrate our technique. ther virtual destinations. Our work focuses on the exploration arXiv:1908.00379v1 [cs.HC] 1 Aug 2019 of vast open worlds – an area where existing local naviga- Author Keywords tion approaches such as the arc-based teleport are not ideally Virtual reality games; navigation; perspectives; virtual avatar; suited and world-in-miniature techniques potentially reduce orientation; virtual body size; world-in-miniature presence. We present a novel alternative for open environments: Our idea is to equip players with the ability to switch CCS Concepts from first-person to a third-person bird’s eye perspective on •Human-centered computing ! Virtual reality; •Software and its engineering ! Interactive games; Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed INTRODUCTION for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the Virtual reality allows players to explore fictional environments author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or in an immersive and natural manner, to experience a feeling of republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]. being there, and almost to forget the real surrounding. Contin- CHI PLAY ’19, October 22–25, 2019, Barcelona, Spain uous technical improvements and faster rendering approaches © 2019 Copyright held by the owner/author(s). Publication rights licensed to ACM. make it possible to push the boundaries of VR even further and ISBN 978-1-4503-6688-5/19/10. $15.00 develop vast open environments that could be explored freely DOI: https://doi.org/10.1145/3311350.3347183 and immersively. However, large and detailed VR worlds Two concepts seem to be of utmost importance when dealing require proper techniques to travel these landscapes. with VR applications: immersion [8] and presence [18]. To stay in line with the majority of recent research, we use the Physical walking using room-scale tracking offers an intuitive term immersion to describe the technical quality of a VR and natural kind of navigation [40]. However, the available setup [6, 45]. Immersive setups can induce a feeling of being walking space is usually confined to the size of a living room. there, which is commonly called presence. This distinction is Game developers overcome this limitation by adding virtual further formalized by Slater et al. [46], Lombard et al. [33] and locomotion techniques such as the prominent teleport (see IJsselsteijn et al. [21]. For a particular focus on locomotion- Figure5). Most of these approaches were designed for local related presence, we point to the work by Slater et al. [47]. navigation and are not ideally suited for exploring large and open worlds. Only a few exceptions exist, such as the world- in-miniature (WIM) [49], where players use a miniature model Cybersickness of the virtual scenario to teleport themselves to distant places. A typical problem most VR applications have to tackle is Nevertheless, this approach relies on an artificial user interface the occurrence of cybersickness [29]. Even though often and does not provide an opportunity to explore an environment being used synonymously with the effect of simulator sick- freely and continuously which potentially reduces the players’ ness [25], both are different strains of the motion sickness phe- possibility to immerse themselves in the virtual world. nomenon [35, 20, 36]. Typical symptoms such as headaches, Our research closes the gap between local teleportation and eye strain, sweating, nausea or vomiting arise due to a mis- WIM relocation by introducing a novel approach for con- match of our vestibular-ocular system. tinuous long-distance traveling. Our main idea is to switch Humans sense acceleration using their vestibular system which dynamically between a first-person and a third-person bird’s usually matches the sensory input gathered from the visual eye perspective on demand. The first-person mode offers a system [29]. In the case of a mismatch between these signals, familiar experience and is used to explore the local surround- the resulting symptoms differ in strength and form [39]. The ing and interact with the environment. In the third-person reason for this body reaction remains unsolved, but so far mode, players see and command their avatar from a bird’s eye three major prominent theories have been established: sensory perspective, as depicted in Figure1. conflict theory (most accepted), poison theory, and postural Using the correct perspective for every situation offers impor- instability theory [29]. The difference between both specific tant benefits [15]: first-person is suited best for interaction- strains of motion sickness was extensively explored by Stan- intensive tasks while third-person provides a better overview. ney et al. [48]: Simulator sickness usually occurs when a We combine both perspectives to achieve an intuitive navi- simulator, typically used for pilot or astronaut training, is not gation approach. Moreover, we extend this basic concept by correctly configured [24]. This technical problem can lead additional features to enhance the experience further: Virtual to rather mild oculomotor and nausea symptoms. In contrast, scaling of the player in third-person mode is used to improve cybersickness is caused by a broad set of reasons ranging from the spatial orientation and deliver a feeling of moving through technological issues such as flickering and lags to a wrong a miniature world while commanding an avatar. Addition- visual image being caused by mismatches in movement, eye ally, we use a smooth and fast transformation between both distance or vergence. The results are mainly severe symptoms perspectives to prevent cybersickness and to emphasize the such as disorientation and nausea [48]. impression of leaving and re-embodying the virtual avatar. Additionally, Hettinger et al. [19] introduced the phenomenon Our main contribution is the proposed navigation technique us- of vection as a possible source for cybersickness. Vection is a ing dynamic perspective switching. We validate this approach feeling of moving that is solely induced by the visual system by comparing it against the arc-based teleport using a 3D ad- and usually experienced when sitting on a standing train and venture game. Our experiments reveal significant benefits to watching the adjacent train accelerating. This effect is sup- spatial orientation and overview while preserving equal levels ported by different factors listed by La Viola Jr [29]: the field of presence, enjoyment, and competence. Additionally, our im- of view (FOV) of the HMD, the optical flow rate, the degree provements prevent adverse effects through cybersickness. As of movement and proximity of objects. In short, close and the final step, we discuss the unique strengths and weaknesses fast-moving objects filling the player’s view combined with of our proposed approach and condense these into a set of a big field of view tend to amplify the amount of perceived design implications that can help developers and practitioners. vection and potential cybersickness. Consequently, Fernandes et al. [13] propose limiting the FOV to reduce cybersickness. A broader discussion about the influence of the FOV on cyber- RELATED WORK sickness can be found in the work of Lin et al. [32]. Our work belongs to the virtual reality research with a particular focus on VR games and locomotion techniques. Conse- Additionally, recent studies have shown that the accumu- quently, we first introduce basic concepts and issues behind lated flow over time, perceived via central and peripheral VR games such as immersion, presence, and cybersickness. vision, forms a critical factor in the occurrence of motion Subsequently, we outline the current state of the art in VR sickness [31]. Instead of avoiding cybersickness at all costs, locomotion research. Since our technique centers around the von Mammen et al. [53] showed that games with artificially concept of perspective-switching and dynamic virtual rescal- induced cybersickness can still be enjoyable. This leads to ing, we also provide the necessary background to these topics. the conclusion

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