ReverseCAVE Experience: Providing Reverse Perspectives forSharing VR Experience
Akira Ishii∗

Masaya Tsuruta∗

Ippei Suzuki

University of Tsukuba
ishii@iplab.cs.tsukuba.ac.jp

Recruit Marketing Partners Co., Ltd.
masaya@r.recruit.co.jp

University of Tsukuba

Shuta Nakamae

Tatsuya Minagawa

Junichi Suzuki

University of Tsukuba

University of Tsukuba

ISI-Dentsu, Ltd.
Open Innovation Lab.

Yoichi Ochiai
University of Tsukuba

(a)

(b)

(c)

(d)

Figure 1: Overview of ReverseCAVE. Conventional situation (a, c) and result of our method applied (b, d). a, b) He is playing
the VR game and interacting with an animal. c, d) He is an actor acting as a creature using a motion capture system. In (a) and(c), it is difficult to understand what he is doing, however, in (b) and (d), we can understand what he is doing in the physicalspace. ReverseCAVE covers “perspective gap.”

ABSTRACT
VR games are currently becoming part of the public-space entertainment (e.g., VR amusement parks). Therefore, VR games should
be attractive for not only players but also observers. However, VRwith HMD is a closed experience among those who are wearing
HMD, and can only be individually experienced by the specific person. We call this “perspective gap.” These perspective gaps exist in
many situations. To address these problems, we present “ReverseCAVE”, a system for sharing the experiences of people in VR withothers (observers). As another application, it is possible to visually
recognize the actual appearance of the person performing the act
at the motion capture studio and the superimposed character at thesame time. ReverseCAVE has four translucent screens surrounding
the player. The VR environment is projected onto the screens. By

this, the observer can see both the physical player and the VR environment experienced by the player simultaneously. Also, in themotion capture system, when viewing the actor from the observer
outside of ReverseCAVE, the character is superimposed to the actor. This makes it look as if the actor is the actual character from theobserver. We enhance the observers’ experience by ReverseCAVE.

CCS CONCEPTS• Human-centered computing → Mixed / augmented reality;

KEYWORDS
Virtual Reality, environmental VR, mixed reality (MR), sharing experience, CAVE, visualization∗ Both authors contributed equally to the work.

SA ’17 VR Showcase, November 27-30, 2017, Bangkok, Thailand© 2017 Copyright held by the owner/author(s).
This is the author’s version of the work. It is posted here for your personal use. Notfor redistribution. The definitive Version of Record was published in Proceedings ofSA ’17 VR Showcase, https://doi.org/10.1145/3139468.3139482.

ACM Reference Format:
Akira Ishii, Masaya Tsuruta, Ippei Suzuki, Shuta Nakamae, Tatsuya Minagawa, Junichi Suzuki, and Yoichi Ochiai. 2017. ReverseCAVE Experience:
Providing Reverse Perspectives for Sharing VR Experience. In Proceedingsof SA ’17 VR Showcase. ACM, New York, NY, USA, 2 pages. https://doi.org/10.1145/3139468.3139482

SA ’17 VR Showcase, November 27-30, 2017, Bangkok, Thailand

1IMPLEMENTATION OVERVIEW

ReverseCAVE consists of a motion capture system, a cubic translucent screen, and projectors, as shown in Figure 2. The motion capture system is used to acquire the position of the observer to calculate the projection position. The VR environment that the player isexperiencing is projected onto the screen. By this, the observer cansee both the physical player and the VR environment. Also, in themotion capture studio, when viewing the actor from the observer’s
side, the character is superimposed to the actor. This makes it look
as if the actor is the character from the observer. The character’s
position is changed corresponding to the position of the actor andobserver. In other words, the character is superimposed on the intersection point of the eye-line (between the observer and actor)
and the projecting plane of ReverseCAVE.

3Translucent screen

INTRODUCTION

Head mounted display (HMD) is rapidly spreading as a device forexperiencing virtual reality (VR). It is important to be able to shareVR experience with others [Biocca and Levy 1995]. However, VRwith HMD is a closed experience among those who are wearing
HMD, and can only be individually experienced by the specific person. In many cases, people without HMD cannot share the experiences with the people wearing HMD. We call this problem “perspective gap.” As a method to solve this problem, for example, SAVE
[Zhu et al. 2016] superimposes the image of the VR player onto theVR environment using chroma key, and displays this to the LCD
monitor. For another example, ShareVR [Gugenheimer et al. 2017]
uses floor projection and mobile displays in combination with position tracking to visualize the VR environment for Non-HMD users.
We focus on these perspective gaps in VR and computer graphics applications. These perspective gaps exist in many situations(e.g., VR games in game shows, actors and observers in the motion capture studio, telepresence situation in conference). To address such problems, we present “ReverseCAVE” [Ishii et al. 2017],a system for sharing the experiences of people in VR environment(player) with others (observers), as shown in Figure 1ab. As another application, it is possible to visually recognize the actual appearance of the person performing the act at the motion capture
studio and the superimposed character at the same time, as shownin Figure 1cd. Similar to CAVE, ReverseCAVE has four screens surrounding the player. The screen’s material in our study, which isa translucent fabric, is different from CAVE. Then the VR environment is projected onto the screens. By this, the observer can see
both the physical player and the VR environment experienced bythe player.

2Ishii and Tsuruta et al.

FUTURE VISION: VR TO EVERYONE

We investigated whether users would want to share their VR experiences with others when using our system with eight participants (all males) aged between 19 and 23 years (mean: 21.6). There
were two experimental conditions, with ReverseCAVE and without
ReverseCAVE. We showed the participants a video of a player experiencing VR (the video version of Figure 1ab), and asked if theywould like to share a video or a photo with others if they were theplayer in the video. “Sharing” here implies both sharing in closed
forums such as Facebook messenger, and sharing on open forums

Sensor for VR

Motion capture camera
HMD
Objectin VR space
MarkerVR player

ProjectorObserver

Figure 2: System components of ReverseCAVE.
such as Instagram. We recorded the participants’ responses using
a 5-point Likert scale.
Based on the result, without ReverseCAVE, the average score was3.1 (SD = 1.27); however, with ReverseCAVE, the average score was4.4 (SD = 0.70). We conjecture that the users were more inclined
towards sharing their experience with others when using ReverseCAVE. Applying the paired t-test, there was a significant difference between with ReverseCAVE and without ReverseCAVE cases(t = -3.99, df = 7, p < 0.01). For without ReverseCAVE condition,
the participant with a score of 2 commented, “I don’t want to sharesomething which other people can’t understand what I am doing, andlooks weird.” For with ReverseCAVE condition, the participant witha score of 5 commented, “I felt it would be fun and easy for others tounderstand by posting it because you can see me play the VR and theactual VR which I’m seeing at the same time.” As described earlier,by using ReverseCAVE, it is possible to share with others what theVR player is experiencing; therefore, the possibility of sharing theexperience with others can be enhanced.
Till today, VR experience was only for the the player. However,by using ReverseCAVE, VR experience can be shared to everyone.
We envision that VR experience is for everyone.

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Akira Ishii, Masaya Tsuruta, Ippei Suzuki, Shuta Nakamae, Tatsuya Minagawa, Junichi
Suzuki, and Yoichi Ochiai. 2017. ReverseCAVE: Providing Reverse Perspectives forSharing VR Experience. In ACM SIGGRAPH 2017 Posters (SIGGRAPH ’17). ACM,New York, NY, USA, Article 28, 2 pages.
Yu Zhu, Kang Zhu, Qiang Fu, Xilin Chen, Huixing Gong, and Jingyi Yu. 2016. SAVE:
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