Let Your World Open
CAVE-based Visualization Methods of Public Virtual Reality towards a Shareable VR Experience
Akira Ishii∗

Masaya Tsuruta∗

Ippei Suzuki

ishii@iplab.cs.tsukuba.ac.jp
Digital Nature Group
University of Tsukuba

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

Digital Nature Group
University of Tsukuba

Shuta Nakamae

Junichi Suzuki

Yoichi Ochiai

IPLAB
University of Tsukuba

ISI-Dentsu, Ltd.
Open Innovation Lab.

wizard@slis.tsukuba.ac.jp
Digital Nature Group
University of Tsukuba

HMD tracker

Translucent screen

Object in VR

Player with
HMD

Bystanders

Bystanders

Projector

Figure 1: Left: Overview and setup of the ReverseCAVE for public VR visualization. Right: Using the ReverseCAVE, bystanders
can see the HMD user (player) and the VR environment simultaneously without an HMD; bystanders can capture photographs
or record videos to share with others.

ABSTRACT
Virtual reality (VR) games are currently becoming part of the publicspace entertainment (e.g., VR amusement parks). Therefore, VR
games should be attractive for players, as well as for bystanders.
Current VR systems are still mostly focused on enhancing the experience of the head-mounted display (HMD) users; thus, bystanders
without an HMD cannot enjoy the experience together with the
HMD users. We propose the “ReverseCAVE”: a proof-of-concept
prototype for public VR visualization using CAVE-based projection with translucent screens for bystanders toward a shareable VRexperience. The screens surround the HMD user and the VR environment is projected onto the screens. This enables the bystanders
to see the HMD user and the VR environment simultaneously. We
designed and implemented the ReverseCAVE, and evaluated it interms of the degree of attention, attractiveness, enjoyment, andshareability, assuming that it is used in a public space. Thus, we∗ Both authors contributed equally to this research.

AH2019, March 11–12, 2019, Reims, France© 2019 Association for Computing Machinery.
This is the author’s version of the work. It is posted here for your personal use.
Not for redistribution. The definitive Version of Record was published in Augmented
Human International Conference 2019 (AH2019), March 11–12, 2019, Reims, France,
https://doi.org/10.1145/3311823.3311860.

can make the VR world more accessible and enhance the public VR
experience of the bystanders via the ReverseCAVE.

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

KEYWORDS
Environmental VR, mixed reality (MR), sharing experience, CAVE.
ACM Reference Format:
Akira Ishii, Masaya Tsuruta, Ippei Suzuki, Shuta Nakamae, Junichi Suzuki,
and Yoichi Ochiai. 2019. Let Your World Open: CAVE-based Visualization
Methods of Public Virtual Reality towards a Shareable VR Experience. In
Augmented Human International Conference 2019 (AH2019), March 11–12,
2019, Reims, France. ACM, New York, NY, USA, 8 pages. https://doi.org/10.
1145/3311823.3311860

1

INTRODUCTION

Virtual reality (VR) games with head-mounted displays (HMDs)
are rapidly increasing and are becoming part of the public-spaceentertainments (e.g., VR amusement parks and video game expositions). According to Biocca and Levy [2], sharing VR with friends
and family is more enjoyable. However, in several cases, people
without an HMD cannot share the experiences of those wearing an

AH2019, March 11–12, 2019, Reims, France
HMD. Therefore, in the current public-space VR entertainment age,
it is important to be able to share VR experiences with bystanders.
One of the commonly employed solutions to this problem is toshow the VR contents those captured from the first-person viewpoint of a player on a large display. Another alternative solution
involves the use of chroma key compositing to share VR experiences through a mixed reality medium [28, 30]. By showing chroma
key composed image using a display, it is possible to share the VR
environment with bystanders.
As previously described, there are several manners throughwhich VR can be shared; however, no study exists in which VRin public spaces has been explored. Therefore, in this study, we
focused on the “shareability” of the VR contents in public spaces. To
enhance the shareability, we propose the “ReverseCAVE” system, inwhich the experiences of the player in the VR environment (HMD
user) can be shared with bystanders (non-HMD users), as shownin Figure 1. The ReverseCAVE has a cubic screen surrounding theplayer, similar to the CAVE [4]. The screens are translucent in order for the bystanders outside the ReverseCAVE to be able to see
the player in it. The VR environment, which is experienced by theplayer, is projected on the screen. Thus, the bystanders can see
both the real player and the VR environment experienced by theplayer. The CAVE is a system for a person who is inside the cubic
screen. In contrast, the ReverseCAVE is a system for persons who
are outside the cubic screen.
We wish to expose the person who is completely isolated in the
VR space to the real world. In addition, we expect our system to be
used in public spaces, such as conventions, video game expositions,and amusement parks (not for domestic use). This is because, forexample, bystanders that wait in line to play VR games at VR game
expositions may become bored. Moreover, people who pass by the
VR booth may not be attracted by the VR games because they do
not have knowledge of the VR contents beforehand and cannot
understand how the contents are exciting. Thus, we were motivated
to excite bystanders by using various visualization methods of VR
games. We were inspired by open-air attractions in theme parks,
such as roller coasters, which can entertain the riders, as well as
the bystanders waiting in line.
In the previous papers, we present the concept of ReverseCAVE [13–15]. Following these previous work, in this paper, we
will present the design of the ReverseCAVE in detail — a proofof-concept implementation — and the results of the in-depth user
studies that were conducted for the evaluation of the ReverseCAVE.
To investigate how the ReverseCAVE can contribute to public-spaceVR, we set the following main research question: “In public-spaceVR, can the ReverseCAVE increase the Degree of attention, Attractiveness, Enjoyment, and Shareability?”. Moreover, we conducteduser studies to compare the ReverseCAVE with other similar methods. This study makes the following contributions.

Ishii and Tsuruta, et al.

2

2.1

Room Projection-based AR

Numerous research works have been conducted in which AR has
been realized by projecting the virtual world on physical objects or aspace in the real world (e.g., [25]). Raskar et al. proposed iLamps [24],a self-configuring hand-held projector, for environment-aware systems. Willson et al. [29] proposed steerable displays that can be used
to superimpose graphics onto physical objects in the real world for
AR and ubiquitous computing scenarios. IllumiRoom [16] is a system that augments the area surrounding a television with projectedvisualizations to enhance traditional gaming experiences. Benkoet al. [1] proposed a spatial AR system that combines dynamic
projection mapping, multiple perspective views, and device-lessinteraction. In addition, there are systems that transform any room
into an immersive and augmented entertainment environment [17]and an AR-based telepresence system [22] using room projection.
These approaches can be used for the sharing of the VR experience; in our study, we used an approach that is similar to theaforementioned. Compared with HMD-based AR (e.g., Microsoft
HoloLens) or a smartphone-based AR, room projection-based AR
has certain advantages: (1) users can experience AR without any additional wearable equipment, and (2) the wider area of the content
is visible because room projection-based AR is not affected by otherthan the human viewing angle. Therefore, room projection-based
AR is suited for the scenario of publicly sharing VR contents inspaces where there is a large number of bystanders.

2.2

Sharing a First-Person Video

Parallel Eyes [18] is a system through which first-person viewpoints can be shared with others simultaneously by using HMDs
and cameras. This system investigates what type of influence will
happen by sharing plural first-person viewpoints in the real world.
Furthermore, the concept of sharing first-person videos has been
explored from various aspects [5, 6, 11, 12, 19, 20, 23].
On the other hand, we aim to observe the person who is experiencing VR and the VR contents simultaneously from a third
perspective, not the first-person viewpoint of the player. By observing the player from a third-person perspective, the observer
can understand both the situation in which the player is and thebackground. Moreover, by using the third-person perspective, theinfluence of motion sickness could be reduced because the screen
does not change according to the movement of the player.

2.3• Design of the ReverseCAVE system to address the problemsof shareability in VR in public spaces.
• Implementation of a proof-of-concept of the ReverseCAVE
to evaluate the feasibility of the design.
• Experimental evaluation of the performance of the ReverseCAVE in public spaces.

RELATED WORK

We will review related work on room projection-based augmented
reality (AR), the sharing of first-person videos, and the sharingof the VR experience; moreover, we will present the focus of thisstudy.

Sharing the VR Experience

This topic is most relevant to our study. Research on sharing the VRexperience with others can be categorized into two types: (1) only
displaying the situation of the VR experience (non-participative,
bystanders do not participate in the game), and (2) both parties
engage with the VR together (participative, bystanders participate
in the game).

Let Your World OpenRight

AH2019, March 11–12, 2019, Reims, France

Back

Right

Back

Tracker

Projector

Back

Left

Right

Left

Left
Front

Front

Front

Figure 2: Relationships between four cameras and each screen for VR projection. Left: Setup of the ReverseCAVE with a cubic
screen. Middle: Captured cubic image for projection (placed on the VR environment for explanation). Right: Rendered images
for each screen plane.
2.3.1 Non-participative Approach. SAVE [30] is a system that enables sharing the experience of people in the VR environment withthose who are outside the VR environment by combining the Kinect
depth camera and the tracking system of the HTC Vive. By using
the viewpoint of the Kinect camera and the positional relationshipof the player, it generates the third-person viewpoint image of the
VR environment that the player is actually experiencing. TransparentHMD [21] is a system that enables bystanders to see theface of the HMD users. Moreover, FrontFace [3] is a system forcommunication between the HMD user and the non-HMD user
using a smartphone attached on an HMD. This provides the eyegaze information of an HMD user to the bystanders (non-HMD
users) for reducing the communication barrier between them. The
ReverseCAVE is categorized into non-participative approach as
well.
2.3.2 Participative Approach. ShareVR [7] enables asymmetric interactions between an HMD user and non-HMD users by employing
floor projection of the VR and a trackable hand-held monitor. Furthermore, research work exists on the sharing of the VR experience
with others by using an additional HMD [9]. A VR system has been
proposed with concurrent tele-collaboration among avatars controlled by and synchronized with multiple users in remote places
using multiple HMDs. Hagler et al. [10] proposed a system thatenabled bystanders to participate in the VR contents using a smartphone. The Maze Commander [26] enables asymmetric interaction
between an HMD user and non-HMD users using the Sifteo Cubes.
In addition, FaceDisplay [8] enables asymmetric interaction between an HMD user and non-HMD bystanders using a modified
HMD that consists of three touch screens and a depth camera attached to its back. Bystanders can understand the VR environment
through the screens and can participate in engaging with the VRcontents via touch or gestures.

2.4

Focus of This Study

The ReverseCAVE is a non-participative approach for the sharingof the VR experience in public spaces. We were inspired by open-air
attractions, such as roller coasters, which can entertain the riders,
as well as the bystanders waiting in line. Such open-air attractions
function as a type of advertisement. The ReverseCAVE can display
the actual VR environment to the real world to attract the attention
of bystanders. In addition, the ReverseCAVE enables and facilitatesshooting photographs with wider variety of aspects because it
adopts a cubic screen.
It should be noted that the interaction between the player andthe bystanders is not so important in public VR experiences because
in many cases at video game expositions, they are not acquainted
with one another. Consequently, the ReverseCAVE does not haveinteractive features.

3

REVERSECAVEThe ReverseCAVE is a system for sharing the VR experiences ofthe player with bystanders. In the past study [14, 15], we used
the motion capture system to acquire the position of the observer
in order to calculate the projection position to maintain visualconsistency for bystanders. However, bystanders are required towear markers in order to use the motion capture system. In addition,in the conventional system, only one person can experience a finedisplay of the VR environment in terms of the precise perspective
and consistency. We assume that the ReverseCAVE is used in public
spaces and there are a lot of bystanders, therefore, we decided not
to use the motion capture system to track them.

3.1

ScreenOur aim is to let the bystanders see both the actual appearance ofthe player and the VR environment that the player is experiencing.
Therefore, the following conditions are necessary.
• In addition to the VR environment, the player himself/herself
must blend into the VR world.
• The player should be visible from bystanders, not be hidden
by surrounding equipment.
To fulfill the above conditions, we adopted a method of surrounding
the four sides of the player using translucent screens and projecting
the VR environment on the screens. By using translucent cloths forthe screen, it is possible to create screens of various shapes, suchas rectangular or cylindrical shapes. In this study, as a proof-ofconcept implementation, we used the cubic screen because it waseasy to assemble.

3.2

Projection

In the ReverseCAVE, the VR environment that the player is experiencing is projected on the screens, as shown in Figure 1. We
mounted four virtual cameras on the head of the player in the VR

AH2019, March 11–12, 2019, Reims, France(a)Display

Chroma key(b)

Ishii and Tsuruta, et al.

(c)

(d)

PlayerReverseCAVE
Walkable area

Figure 3: Setup of Study 1. (a) Layout of the VR game booths. Participants walk around in the walkable area and see the VRbooths. (b) First-person view (FPV) and Chroma key. (c) Contents of the display. (d) ReverseCAVE.
software (Figure 2). Each of the four cameras was aligned alongeach of the screen’s cardinal directions (front, back, left, and right)
to capture the VR environment and to project it on the cubic screen(four translucent walls). The images recorded with each virtual
camera are projected on the screens with each projector.

3.3

Equipment

The equipment we used to demonstrate the proof-of-concept was
the following. As the cubic screen, we used a white mosquito net,
which is a translucent roughly knit cloth with resin fibers (diameterof approximately 0.2 mm). It is a material that diffusely reflects
images moderately, and can be looked through from one side to
the other side. By using this screen, we could simultaneously see
the images projected on the screens and observe the player inside the cubic screen. The projector was the OPTOMA EH320UST,
which is a high-intensity short-focus projector. The resolution was
1920 × 1080 pixels and the brightness was 4,000 lm. Each projector
was placed against each of the four walls of the cubic screen. One
computer was utilized to operate the ReverseCAVE, while driving
the projection and the VR system. The computer had an Intel Core
i7-6700K processor, 32 GB of memory, and two NVIDIA GeForceGTX 1080 graphics boards. Unity (game engine) was used for thecreation of the projected images of the ReverseCAVE.

4STUDY 1: THE DEGREE OF ATTENTION,ATTRACTIVENESS, ENJOYMENT, AND
SHAREABILITY

Assuming that the ReverseCAVE is used in public spaces (e.g., video
game expositions), we evaluated it in terms of the degree of attention, attractiveness, enjoyment, and shareability by comparing itwith conventional methods for the visualization of VR games. We
created an exhibition area for video game expositions in the meeting room. The floor layout is shown in Figure 3a. We demonstrated
a zombie VR game (the player fights against the zombie), which
we created with Unity and Steam VR by using three visualization
methods: the first-person view (FPV), the Chroma key, and theReverseCAVE. Then, the participants evaluated the three sharing
methods in terms of the four aforementioned aspects as visitors ofa video game exposition.

4.1

Study Design

The study was conducted using a repeated measures design with
one independent variable. The independent variable was the visualization method (FPV, Chroma key, ReverseCAVE). The FPV is themost basic method for the visualization of VR contents. The FPV
displays the first-person view of the player on a large TV monitor(Figure 3b). The Chroma key is the synthesis method in which agreen screen is used for the capturing of the player who is standing
in front of the green screen; the player is superimposed onto the
VR environment [28, 30]. Participants would achieve a more spatial
representation of the virtual environment. We used a web camera(Logicool C270 HD Webcam, 1280 × 720 pixels, 30 fps) to capture
the player and Chroma Key Kit plugin of Unity [27] to implement
the Chroma key. The visualization via the FPV and the Chroma
key was prerecorded and displayed on a single display to keep
consistency within the participants, as shown in Figure 3c.
We created questionnaires related to the degree of attention,
attractiveness, enjoyment, and shareability, which were rated on
a 5-point Likert scale. The participants rated each visualization
method and justified their rating.

4.2

Procedure

The study was conducted in a university meeting room. The room
was dim for the purposes of projection. The participants participated in the study as visitors at a video game exposition. After abrief introduction, the participants answered a demographics questionnaire. Then, our staff began to play the zombie VR game at eachexhibition booth and the participants began the evaluation of thevisualization methods as visitors of a video game exposition. The
participants were asked to walk around to observe each exhibitionbooth freely and to complete the questionnaires related to the visualization methods. We informed the participants that whether
the content was good or bad was entirely irrelevant to the evaluation; therefore, we asked them to evaluate solely the visualization
method, and not the content. Until the participants completed tofill the questionnaires, our staff continued to play the VR game. The
study required 33 min on average and the participants received a
500 JPY Amazon gift code (approximately 4.5 USD).

4.3

Participants and Apparatus

Ten participants (1 female and 9 males), aged between 21 and 26
years (M = 23.2, SD = 1.3) were recruited for participation in the experiment. Three participants had normal vision, seven participants
had corrected vision, six wore glasses, and one wore contact lenses.

Let Your World Open

AH2019, March 11–12, 2019, Reims, France

Degree of attention

Enjoyment

If you imagine that you were at a video game exposition,

you think that you would stop in front of the booth andQ1 doobserve the content of the VR game?

M

SD

F

2.60 1.17

C

3.20 1.14

R

4.20 0.42

Q4

Did you feel that the situation of the demonstrationof the VR game was enjoyable?

F

2.50 1.08

C

3.70 1.06

R

4.50 0.53

Q5
Attractivenessyou feel that the situation of the demonstration of
Q2 Didthe VR game was attractive (fun, interesting)?

F

3.00 1.05

C

3.40 1.07

R

4.40 0.70
Did you think that by using this visualization

the contents of the VR game would
Q3 method,
be attractive (fun, interesting) to you?

MSD

Did you think that by using this visualization method,
the contents of the VR game will be enjoyable to you?

F

2.60 1.17

C

3.70 0.95

R

4.00 0.67

Shareability

Q6

Did you want to share the situation of
the demonstration of the VR game withothers (e.g., talk to friends, post on SNS)?

F

3.20 1.14

F

2.10 1.37

C

3.90 0.99

C

3.20 1.40

R

4.30 0.67

R

4.30 0.48

Q7
1Strongly
disagree2

3
Neutral45Strongly
agree

F: First-person view
C: Chroma key
R: ReverseCAVE

Did you want to share the contents of
the VR game with others?

F

2.30 1.06

C

3.10 1.29

R

3.30 1.25

Figure 4: Results of Study 1 (5-point Likert scale).
They had an average experience with VR devices of 1.2 months(SD = 2.6). Their average interest in VR technology was very high(M = 4.0, SD = 1.2) and their average motivation to play VR gamesin the following 12 months was very high as well (M = 4.0, SD = 1.2).
All results were measured on a 5-point Likert scales.
In the experiment, we used the same equipment described in
Section 3.3 for the ReverseCAVE, as shown in Figure 3d. For the
FPV and the Chroma key, we used a SONY BRAVIA FHD TV (KDL52X5050, 52 inch) to display the VR environment. Two videos wereshown on one TV monitor, therefore, each video was scaled to
26 inch.

4.4

ResultThe scores that each visualization method received are illustrated
in Figure 4. We analyzed the results of the Likert scale scores with aFriedman test at a significance level of 5%. The independent variable

was the visualization methods and the dependent variable was theLikert scale score of each questionnaire.
4.4.1 Degree of Attention. For Q1, a Friedman test revealed thatthe ratings were significantly affected by the visualization method(χ(2) = 12.20, p < 0.01). The post-hoc test revealed that the ReverseCAVE was rated significantly higher in terms of attention thanthe FPV (p < 0.01).
4.4.2 Attractiveness. For Q2 and Q3, a Friedman test revealed thatthe ratings were significantly affected by the visualization method(Q2: χ(2) = 9.74, p < 0.01, Q3: χ(2) = 9.19, p < 0.05). The post-hoc
test revealed that the ReverseCAVE was rated significantly higher
with respect to attractiveness both in terms of the situation (Q2)and the content (Q3) than the FPV (Q2: p < 0.05, Q3: p < 0.05).
4.4.3 Enjoyment. For Q4 and Q5, a Friedman test revealed that the
ratings were significantly affected by the visualization method (Q4:

AH2019, March 11–12, 2019, Reims, France
χ(2) = 11.41, p < 0.01, Q5: χ (2) = 11.08, p < 0.01). The post-hoc
test revealed that the ReverseCAVE was rated as significantly moreenjoyable both in terms of the situation (Q4) and the content (Q5)than the FPV (Q4: p < 0.01, Q5: p < 0.05).
4.4.4 Shareability. For Q6, a Friedman test revealed that the
ratings were significantly affected by the visualization method(χ(2) = 11.53, p < 0.01). The post-hoc test revealed that the ReverseCAVE was rated as significantly more shareable in terms of
the situation than the FPV (Q4: p < 0.01). For Q7, there was no significant difference among the visualization methods (χ (2) = 5.85,
p = 0.05).

5

STUDY 2: SHAREABILITY ON SOCIAL
NETWORKING SERVICES (SNSS)

In Study 1, the ReverseCAVE was prone to achieve the most positive rating than other methods; however, there were no significant
differences between the Chroma key and the ReverseCAVE. Therefore, to gain insight on the shareability of each method on SNSs,
we organized a workshop of photo shoot on VR games in public
spaces for the purpose of sharing photographs on SNSs (e.g., Facebook, Twitter, Instagram) and we explored the differences among
the photographs that were captured for each visualization method.
We installed an exhibition area for a video game exposition in the
public space of the university, as shown in Figure 5. We demonstrated the same VR game in Study 1 using the Chroma key andthe ReverseCAVE. Then, participants captured photographs of thesituation in order to freely share them on SNSs as visitors at thevideo game exposition. We observed the photographs from two
viewpoints: the sharing context and the spatial variety of the shots.

5.1

Study Design

We used two visualization methods: the Chroma key and the ReverseCAVE. We divided participants into two groups: one group
captured SNS photographs of the VR game with the Chroma key
and the other group captured photographs of the VR game with
the ReverseCAVE.

5.2

Procedure

The study was conducted in a university public space. The participants participated in the study as visitors at a video game exposition.
After a brief introduction, our staff started playing the zombie VR
game at the exhibition booth. The participants were told to capture
photographs of the VR games and freely share them on SNSs. To
simulate a more realistic situation, we designed the study in orderfor the participants to feel as if they visited a video game exposition
with their friend; we instructed the participants to imagine that
our staff who was playing the VR game was their friend. After theparticipants completed the task of capturing SNS photographs, we
asked them to type a text as a post (e.g., a tweet accompanying
the photograph). We asked the participants to make a post as theywould normally do; thus, we allowed any photograph processing(e.g., color filter on Instagram). The study required an average of
8 min.

Ishii and Tsuruta, et al.

Smartphone
(b)

(a)

Figure 5: Setup of Study 2. (a) Chroma key. (b) ReverseCAVE. The participants captured photographs of the situation (their friend was playing the VR games) to freely shareon SNSs as a visitor at a video game exposition. Then, they
typed a text to be shared together with the photograph.

5.3

Participants and Apparatus

Twelve participants (2 females and 10 males) aged between 18 and24 years (M = 21.3, SD = 1.7) participated in the experiment. They
were majoring in computer science. These participants did notparticipate in Study 1. We used the same apparatus as in Study 1,
and we only showed the real time Chroma key composed image on
a TV monitor (SONY BRAVIA FHD TV KDL-52X5050, 52 inch).

5.4

Result

The photographs captured by the participants are shown in Figure 6. We evaluated the SNS photographs from two viewpoints: thesharing context and the spatial variety of the shots.
5.4.1 Sharing Context. With the Chroma key method, we observedthat participants mainly focused on and emphasized the VR player
when they were capturing the photographs, and they were noteager to shoot the content itself. Three of six participants mainly
captured the VR player (P1, P2, P3). On the other hand, with theReverseCAVE, the participants were focused both on the VR player
and the VR environment.
5.4.2 Variety of Shots. With the Chroma key method, the participants made efforts to capture photographs that included both the
VR player and the TV display in the same frame, in front of theplayer. In contrast, with the ReverseCAVE, the participants were eager to walk around the cubic screen to find the best angle to capture
a photograph, and the variety of the viewpoints of the photographs
was wider than that of the Chroma key photographs. With theReverseCAVE, the photographs were taken from not only the front
side but also the back side of the player. Four of six photographs
were taken from back side of the player (P7, P9, P10, P11), which is
unique to the ReverseCAVE condition.

6

DISCUSSIONSIn the Study 1, we asked participants to state their feelings in theform of free writing. Participant 1 (P1) commented ”I felt that it wasdifficult to completely understand the VR contents via the informationfrom only the FPV or the Chroma key. On the other hand, I felt that
the ReverseCAVE clearly informed me about both the player’s viewand feelings, so this is better for understanding the situation.” P5

Let Your World Open

AH2019, March 11–12, 2019, Reims, France
ReverseCAVE

Chroma key
P1

P4

P2

P5

P3

P7

P6

P8

P10

P9

P11

P12

Figure 6: Result of Study 2. Each text accompanying the photograph as a post was as follows. P1: Blank. P2: “Awesome!!” P3:“[Friend name] looks like fun XD.” P4: “He is fighting, but he is going to lose. #vr” P5: “[Friend name] is fighting now.” P6: “Whatis this!? so funny lol.” P7: “[Friend name] is awesome.” P8: “Hey! This is new zombie game!” P9: “Zombie and a man.” P10: “Wow,he looks too weak. lol. [Friend name] is the no.1 person who is definitely knocked down when a zombie comes.” P11: “Fighting[Friend name].” P12: “He’s really scared of the zombie. lol.”commented “Usually, I feel strange in cases where the player wears
an HMD, but I actually didn’t feel strange at all this time (with theReverseCAVE).” According to these comments, the ReverseCAVE
has an advantage in terms of sharing and visualization of the VRcontents.
Meanwhile, certain shortcomings were pointed out. P8 commented “I like the ReverseCAVE better than the other methods, but
the player was slightly obscure because the environment was dark.”
P10 commented “[...] I’ve never seen anything like this (the ReverseCAVE) before and it felt interesting in terms of being able to directly
see the player through the virtual image, but the image is slightly
low-contrast and it felt somewhat unpleasant because the display is
cubic; not truly 360◦ (cylindrical) [...].” The ReverseCAVE needs forthe environment to be moderately dark because of the projection.
The light of projectors can be used as the lighting of the player. This
enables the bystanders to see the player in dark rooms. However,this lighting depends on the brightness of the projected content.
In the experiment, we used the zombie VR game, in which thebrightness of the stage was relatively low. To solve this problem,
we plan to use a different light source for the lighting of the player(e.g., install LEDs in the frames of the cubic screen).
From Study 1, we obtained an interesting result. Regarding theshareability, the ratings of Q6 and Q7 were similar for the FPV
and the Chroma key. However, for the ReverseCAVE, the ratingsof Q6 and Q7 were not similar and the rating of Q7 was lower.
P3 commented ”I think that the topic of the visualization method(ReverseCAVE) might come up first in a conversation. The topic of
the VR content is not as likely to come up in a conversation.” P10commented “The visualization method (ReverseCAVE) may catch agreat deal of attention and people might be not interested in the VRcontent very much.” The ReverseCAVE is an eccentric and appealingvisualization method; therefore, sometimes the ReverseCAVE ismore prominent and appealing than the VR contents.

7

LIMITATIONS AND FUTURE WORK

Because the ReverseCAVE requires the player to be enclosed within
the translucent screens, the movement of the player is limited.
Therefore, VR contents which require wider space are difficult tobe applied to our current system. On the other hand, contents that
require narrower spaces, such as games in video game expositions
or advertisement demonstrations, are suitable for application to the
ReverseCAVE.
Moreover, our system employs a short-focus digital light processing (DLP) projector, the light source of which generates highbrightness. However, the ReverseCAVE requires a moderately dark
environment in order for appropriate projection luminance to be
maintained.
In the future, we will explore the transparency and open (nonscreen) area of the surrounding screen to study how these parameters effect the bystanders’ impression. For example, we will compare
impressions of bystanders when they observe the VR player surrounded by three displays from one open side with the impressionsof this study.
We also plan to increase the number of contents and participants
to normalize these effects. We will test compatibility between the
VR visualization methods and the displayed contents.
We simulated a VR game exposition in a public space for ouruser studies; thus, the result obtained may be limited. Therefore,
we will conduct further user studies at real public spaces in orderto verify that the results of the present work are in agreement withthe results obtained at real public spaces.

8

CONCLUSION

In this work, the ReverseCAVE was presented, which is a proof-ofconcept prototype for public VR visualization using a CAVE-based
projection with translucent screens to achieve a shareable VR experience with the bystanders. In this paper, a proof-of-concept implementation of the ReverseCAVE was presented and user studies
were conducted to evaluate the ReverseCAVE. First, we considered
the focus of this study and proposed that the ReverseCAVE would

AH2019, March 11–12, 2019, Reims, France
be suitable for public-space VR. Under the above assumption, we
evaluated the ReverseCAVE by comparing with conventional methods and we explored four different aspects for each visualization
method in a video game exposition. As a result, the chroma key compositing (existing method) and the ReverseCAVE were preferredin the context of sharing VR experiences in public spaces. Finally,
we organized a workshop of VR games photo shoot for SNSs andexplored the differences among the photographs that were captured
for each visualization method. As a result, with the ReverseCAVE,
the participants were more motivated to capture photographs witha wide variety of angles and viewpoints than with the chroma
key compositing, and captured a higher number of photographsthat included both the player and the contents. Consequently, theReverseCAVE increased the degree of attention, attractiveness, enjoyment, and shareability in public VR experiences and enabled
the sharing of the VR environment in an engaging and interestingmanner.

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