Optimized HMD System for Underwater VR Experience
Hiroyuki Osone

University of Tsukuba
soneo.tsukuba@gmail.com

Takatoshi Yoshida

The University of Tokyo
takatoshi yoshida@ipc.i.u-tokyo.ac.
jp

Yoichi Ochiai

University of Tsukuba
wizard@slis.tsukuba.ac.jp

Figure 1: We have optically designed the HMD so that it has a sufficient field of view even when the internal structure is filledwith water. This reduced the buoyancy, and so the user can swim comfortably while experiencing VR.

CCS CONCEPTS•Human-centered computing →Virtual reality;

KEYWORDS
Head-mounted display. Virtual reality. Visuohaptic interaction.
ACM Reference format:
Hiroyuki Osone, Takatoshi Yoshida, and Yoichi Ochiai. 2017. Optimized
HMD System for Underwater VR Experience. In Proceedings of SIGGRAPH’17 Posters, Los Angeles, CA, USA, July 30 - August 03, 2017, 2 pages.
DOI: 10.1145/3102163.3102232

1INTRODUCTION

Many people exercise in water. However, when they swim in thepool, they may get bored. Therefore, studies on virtural reality(VR) and augmented reality (AR) in water have been made. Aquacave[Yamashita et al. 2016] allows you to experience VR in anaquarium. The payload is low but the cost of setting up the environment is high. We cannot swim, over a wide area, and so it cannot
be used by many people. Zhang, Tan, and Chen (2016) have created a head-mounted display (HMD)[Zhang et al. 2016] that can beused underwater, but in this structure, air enters the device, which
greatly increases the buoyancy, making swimming uncomfortable.
In Quarles (2015)[Quarles 2015], water was present in the internal
structure of the HMD, but its optical impact was not discussed,
the viewing angle is unknown. Therefore, we designed an optimal
HMD for swimming. Because there was no air layer in the HMD,
it was expected that buoyancy would not be an issue and that theHMD could easily be worn while swimming. Our study is the firstto evaluate underwater VR by subject experiments.
SIGGRAPH ’17 Posters, Los Angeles, CA, USA© 2017 Copyright held by the owner/author(s). This is the author’s version of thework. It is posted here for your personal use. Not for redistribution. The definitive
Version of Record was published in Proceedings of SIGGRAPH ’17 Posters, July 30 August 03, 2017, http://dx.doi.org/10.1145/3102163.3102232.

Figure 2: A map of related work (underwater VR/AR).

2DESIGNING UNDERWATER HMD

In this section, we explain our HMD configuration, which uses
smartphones, planoconvex lenses and underwater goggles designed
for this study. First, as a prototype, we attached the lens of theGoogle Cardboard to underwater goggles and watched a video of
Google Cardboard content for two eyes underwater. However, theimage was located at the center of the field of view, and three images
were formed. Therefore, we developed an optical design, using
Zemax OpticStudio, that enabled the screen to be seen underwaterwith almost the same viewing field as that provided by Google
Cardboard out of the water. Because the focus and the image aresymmetrical, we only needed to consider the optical design for
one eye. First, as shown in figure 3, the optical system of Google
Cardboard, when used in air, was reproduced in OpticStudio. We
used an iPhone 7 as the display unit. The vertical width of theFigure 3: Left: Optical design of Google Cardboard. Right:
Our designed HMD.

SIGGRAPH ’17 Posters, July 30 - August 03, 2017, Los Angeles, CA, USA
Table 1: Lens data.

H. Osone et. al.

QyQz-Variablelength-shown in figure 4. These figures show that when a person puts on awatertight HMD, the head floats in the water, but when the person
puts on our designed HMD, the head sinks in the water.

-9.08

-5.11

320
22.5
25
30

45.8
51.7
65.8
69.9

-10.13
-9.77
-8.38
-8.02

-8.00
-6.42
-4.13
-3.73

Diameter

Focal lengthGoogle
Cardboard
2022.52530system was 58.00mm when it was laid sideways, so we set one rayfrom a height of 29.0 mm and another ray from the center, 0 mm.
The wavelength of the ray was set to 590 nm, which is a general
wavelength that defines the focal length of the lens. The eye model
downloaded and used on the official site of Zemax was used. The
center of the retina of the eyeball model was set as the origin of
the coordinate system. When reproducing the optical system using
Google Cardboard in the air, the coordinates of a ray coming froma height of y = 29.0 mm reached the retina as shown in figure 3.
This figure also shows the optical system for a ray with y = 0 mm.
It is designed so that the coordinates of the image formed by theretina are almost the same as when the Google Cardboard is usedin air. We tried each of the plano-convex lenses sold by Edmund
Optics one by one, and repeated the optimization calculations forthe image on the retina with the distance between the display andthe lens as a variable. For each lens, the coordinates for a ray with
y = 29 mm reaching the retina were examined as shown in table
1. Therefore, we used a lens with a diameter of 25 mm and a focal
length of 25 mm, whose coordinates were closest to the coordinates
when using Google Cardboard. The HMD was designed by laser
cutting acrylic material. Because vision is different for each person,a mechanism was provided that allows adjustment of the focus byvarying the distance between the display and the lens. Specifically,a vertical hole was made in the upper part and side of the HMD
and screws were passed through it. We designed a 3D model of theEVALUATION

Five volunteers (ages 18-21, 0 female) were recruited. Their averageheight and weight were 171.6 cm (SD=3.2, range 169-175) and 62.4
kg (SD=9.3, range 50-79). All participants had normal or correctedvision. Two types of HMD were prepared in the experiment. The
first was a water-tightened off-the-shelf HMD with adhesive andvinyl tape. It was fixed in a position that was in focus for one ofthe authors. The second was an HMD with a structure that allowed
water to fill inside. Subjects swam freely while looking at a 360
movie delivered as content for Google Cardboard from Youtube
using an iPhone 7. The movie movie screen moves according to
the movement of the head by using the motion detection capabilities of the accelerometer and gyro sensor of the iPhone 7. Whenthe subjects swam, they wore a snorkel, nose plugs, and earplugs
depending on their choice. Visibility in a wide field of view wasevaluated by the subjects using a seven-level scoring system (0 =unsatisfied, 6 = satisfied). For the watertight HMD, the average was3.0 (SD = 2.2). For our HMD we made, the average was 3.8 (SD =1.47). This result proved that there was sufficient field of vision.
We asked each subject to compare the ease of moving their head
underwater (0 = unsatisfied, 6 = satisfied), both for the watertight
HMD with large buoyancy and for the HMD with low buoyancy
designed by us. For the watertight HMD, the average was 3.2 (SD= 0.9). For our HMD, the average was 3.6 (SD = 1.7). This result
proved that players can swim comfortably by wearing an HMD withless buoyant force. We used factor analysis of an iGroup Presence
Questionnaire (iPQ) [igroup org 2010] to evaluate the immersion
feeling. In a watertight HMD, the overall presence of all reported
participants was reported as 2.78 / 6 (SD = 1.72). Spatial Presence
was reported as M = 2.92, (SD = 1.83), Involvement as M = 2.70 (SD =1.22), and Realness as M = 2.70 (SD = 1.55). In the HMD, the overall
presence of all reported participants was 3.31 (SD = 1.72). SpatialPresence was reported as M = 3.15 (SD = 0.96) for, Involvement as
M = 3.52, (SD = 1.70), , Realness as M = 3.40 (SD = 0.47). From thisresult, we can infer that though the participants were engaged withand were present in the virtual underwater world, they behaved asif they were actualy scuba diving. In other words, our HMD madeit possible to experience the virtual world more naturally.

REFERENCES
Figure 4: Left: Watertight HMD. Right: Our designed HMD.
M 1 is the centroid of the enclosure. M 2 is the overall centroid.
enclosure using Rhinoceros. For the sake of simplicity, the head
was a ball with a diameter of 20 mm and a weight of 5 kg, and its
center was set as the origin of the coordinates. For other objects,
the weight was measured and the volume was calculated from themodel. The volumes of the tape and adhesive were ignored. Therelationship between the center of gravity, weight, volume and soon is shown in the figure. The coordinates in each HMD are set as

igroup org. 2010. igroup Presence Questionnaire (IPQ) overview. http://igroup.org/pq/ipq/index.php. (2010).
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