Easy rearward visibility by the control of eye direction
in viewing panoramic images with HMD
Seitaro Inagaki

Kenji Funahashi

Nagoya Institute of Technology, japan
s.inagaki.706@stn.nitech.ac.jp

Nagoya Institute of Technology, Japankenji@nitech.ac.jp

Scenery seen when the real eye
direction is 0 degrees

Scenery seen when the real eye
direction is 30 degrees

Scenery seen when the real eye
direction is 60 degrees

Scenery seen when the real eye
direction is 90 degrees

Sensor0°

Real eyedirection

Virtual eye
direction

60°

92°

HMD

(a)

(b) -180°

Angle of eye direction 0°

30°

60°

180°

90°

(c)

180°
Rearward

Figure 1: (a) Appearance of experiment, (b) Example of panoramic 360-degree image used in the experiment, (c) Schematic
diagram when the angle in the real eye direction is 60-degree

CCS CONCEPTS• Human-centered computing → Human computer interaction (HCI).

KEYWORDS
HMD panoramic view, eye direction control, rearward visibility
ACM Reference Format:
Seitaro Inagaki and Kenji Funahashi. 2022. Easy rearward visibility by thecontrol of eye direction in viewing panoramic images with HMD. In Special
Interest Group on Computer Graphics and Interactive Techniques Conference
Posters (SIGGRAPH ’22 Posters), August 07-11, 2022. ACM, New York, NY,USA, 2 pages. https://doi.org/10.1145/3532719.3543210

1INTRODUCTION

The development of home-use HMDs has made it possible for many
people to enjoy VR in the comfort of their own homes. Most VR
services that allow users to view 360-degree images are used in aseated position. However, it is difficult for users to look rearward
while rotating the necks and hips in a seated position [K.Yonemotoand T.Kondo 1995]. Sitting in a swivel chair makes it easier to lookrearward, but it has been reported that when viewing 360-degree
images with an HMD, the rotation of the seat surface amplifies theuser’s body movements, resulting in a larger sensory discrepancy[Y.Banchi and T.Kawai 2018]. In this paper, we propose a new
method that enables rearward viewing while sitting in a chair. The
direction in which the user looks is called the eye direction. By
presenting a rearward view on the HMD that is different from theactual viewing direction, the user can have a rearward view without
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ACM ISBN 978-1-4503-9361-4/22/08.
https://doi.org/10.1145/3532719.3543210

having to sit up (Figure 1). We also examine better way to display
how much differently rearward is displayed on various parameters.

2

EYE DIRECTION EXAGGERATION METHOD

The direction in which the viewer is actually looking, regardless ofthe scenery displayed on the HMD, is called the “real eye direction”
and the direction of the scenery displayed on the HMD by the program is called the “virtual eye direction.” The virtual eye direction isbasically the same as the real eye direction, but the angle of the realeye direction is exaggerated to display the scenery on the HMD in a
virtual eye direction different from the real eye direction (Figure 2).
This angle at which the virtual eye direction differs from the realeye direction is called the “change point.” Assuming that the angle
in the real eye direction is 𝑟 degrees (−90 ≤ 𝑟 ≤ 90), the angle inthe virtual eye direction is 𝑣 degrees (−180 ≤ 𝑣 ≤ 180), and theangle of the change point is 𝑎 degree (0 ≤ 𝑎 ≤ 90), then consider
the following equation (Figure 3).
𝑣 = 𝑒 (𝑟 ) (|𝑟 | ≤ 𝑎)(1)
𝑣 = 𝑓 (𝑟 ) (|𝑟 | > 𝑎)
Here 𝑒 (𝑟 ) and 𝑓 (𝑟 ) are functions of 𝑟 . Now, noting that 𝑟 ≥ 0,𝑣 ≥ 0, and considering the new coordinate axes 𝑟 ′ and 𝑣 ′ , 𝑒 ′ (𝑟 ′ )and 𝑓 ′ (𝑟 ′ ) can be defined as follows. And substitute Equation (2)into Equation (1) to determine 𝑒 (𝑟 ) and 𝑓 (𝑟 ), as Equation (3).
 ′𝑣 = 𝑒 (𝑟 ′ + 𝑎) − 𝑎 = 𝑒 ′ (𝑟 ′ )(2)𝑣 ′ = 𝑓 (𝑟 ′ + 𝑎) − 𝑎 = 𝑓 ′ (𝑟 ′ ) ′𝑒 (𝑟 − 𝑎) + 𝑎 = 𝑒 (𝑟 )(3)𝑓 ′ (𝑟 − 𝑎) + 𝑎 = 𝑓 (𝑟 )Considering 𝑑 (𝑟 ) that is the difference between 𝑒 (𝑟 ) and 𝑓 (𝑟 )(𝑟 ≥ 0), 𝑑 ′ (𝑟 ′ ) can be defined as folows,𝑑 ′ (𝑟 ′ )=𝑑 (𝑟 ) = 𝑓 (𝑟 ) − 𝑒 (𝑟 )(4)𝑓 (𝑟 ) = 𝑑 (𝑟 ) + 𝑒 (𝑟 )′ ′′ ′′′𝑓 (𝑟 ) − 𝑒 (𝑟 ) = 𝑓 (𝑟 + 𝑎) − 𝑒 (𝑟 + 𝑎) = 𝑓 (𝑟 ) − 𝑒 (𝑟 )=𝑑 (𝑟 )

(5)

SIGGRAPH ’22 Posters, August 07-11, 2022, Vancouver, BC, Canada

S.Inagaki et al.

Here, noting that the change point is the origin, we consider difference between real eye direction and virtual eye direction asfollows,𝑑 ′ (𝑟 ′ ) = 𝑏𝑟 ′𝑐 (𝑐 ⊆ 𝑁 )(6)
Parameter 𝑐 (𝑐 ⊆ 𝑁 ) is called “variation type” and the slope of thetangent line to 𝑑 ′ (𝑟 ′ ) at 𝑟 ′ = 0 is zero, except when 𝑐 = 1. So we
obtain Equation (7) and consider again Equation (1) as Equation (8).

Average of Statisfaction Score𝑓 (𝑟 ) = 𝑒 (𝑟 ) + 𝑑 (𝑟 ) = 𝑒 (𝑟 ) + 𝑑 ′ (𝑟 − 𝑎)(7)

EXPERIMENTS

Two experiments were conducted. In the first experiment, we tested
for problems with exaggeration and explored the most appropriateexaggeration. Twelve different exaggeration patterns (3 types ofparameter 𝑐 and 4 types of parameter 𝑎) were prepared for theexperiment. Subjects were asked to use the HMD to randomly
try new methods in all exaggeration patterns and to answer aquestionnaire. The questionnaire asked about “usability” of use and“discomfort.” We defined "satisfaction" as the score for usability ofuse minus the score for discomfort, and used this score to determine
Sensor0°45°0-0.50)

5)ag(Ex3,4ag(Ex3,6)0)

3,0

3,3ag
(ag(ExEx0)

5)

ag(Ex2,4ag(Ex2,6)

0)

2,0

2,3ag
(ag(ExEx0)

5)ag(1,6ag(Ex1,40)
Ex

1,31,0)-1ag(𝑣 = 𝑒 (𝑟 ) = 𝑟 (|𝑟 | ≤ 𝑎)(8)
𝑣 = 𝑓 (𝑟 ) = 𝑟 ± 𝑏 |𝑟 − 𝑎|𝑐 (|𝑟 | > 𝑎)
The addition and subtraction signs in the Equation (8) are calculated as addition for right-handed rotation and subtraction for lefthanded rotation. We change parameter 𝑐 and 𝑎 like Figure 4, andcall “Exag(c,a).” The numbers in parentheses indicate the variation
type on the right and the angle of the change point on the left. For
example, the virtual eye direction is the real eye direction the sameas up to 30 degrees, and it is exaggerated quadratically from 30
degrees in Exag(2,30).

10.5

Ex𝑒 (𝑟 ) + 𝑏 · (𝑟 − 𝑎)

𝑐

2
1.5ag
(==

33
2.5

Ex𝑣

4
3.5

Figure 5: Result for appropriate exaggeration
the superiority of the exaggerated patterns. This relationship wasobtained from preliminary experiments. The results are shown inFigure 5, which shows that among the 12 exaggeration patterns,Exag(1,0) has the highest score of satisfaction, and the larger theangle of the change point, the lower the degree of satisfaction. It isconfirmed that low-order, near-linear exaggeration is preferred.
The second experiment examined the usefulness of the proposedexaggeration method. Subjects responded with an image of theusefulness of our method that more closely resembled actual use.
Subjects tried two display ways, assuming that they would enjoy
panoramic 360-degree image of foreign tourist destination. One was
the most satisfactory Exag(1,0) in the first experiment; the order
was the normal condition (no exaggeration). As a result, four outof four subjects responded that it was difficult to see rearward in
the normal condition, but that exaggeration made it easier to see
rearward.

Real eyedirection

4

Virtual eye
direction
HMD

(a)

180°
Rearward(b)

Figure 2: (a) Normal real and virtual eye direction, (b) Realand virtual eye direction of this system𝒅(𝒓)𝒆 𝒓 =𝒓90°𝒓!

𝒂0𝒂90°𝒓

180180180165165

165

150150150

1351201059075604530135120105907560453010590754530150030456075900

eye direction

1530456075

90

0

The angle of the real(b)eye direction

REFERENCES

60

15

The angle of the realThis work is supported in part by JSPS KAKENHI Grant Number
JP20K11918.

12001515304560

7590

The angle of the real(c)We proposed a new method that enables rearward visibility while
sitting in a chair and conducted two experiments to see if there
were any problems with exaggeration. As a result, it was confirmedthat this method facilitates rearward visibility and allows easy
enjoyment of scenery in all directions. As a future work, we would
like to further suppress VR sickness and find a better exaggeration
method that is closer to the actual VR use.

ACKNOWLEDGMENTS

135

150(a)

The angle of the virtual eye direction𝒇(𝒓)The angle of the virtual eye direction𝒗′

The angle of the virtual eye direction𝒗
180°

COUCLUSION

eye direction

Figure 3: Concep- Figure 4: Example of exaggerated
tual Diagram
pattern: (a) Exag(1,0), (b) Exag(2,30),(c) Exag(3,45)

S.Ishigami K.Yonemoto and T.Kondo. 1995. Joint range of motion display and measurement methods. The Japanese Journal of Rehabilitation Medicine 32, 4 (1995),
207–217.
K.Yoshikawa Y.Banchi and T.Kawai. 2018. Effect of chair swiveling on user experienceduring 360-degree images viewing using a HMD. TVRSJ 23, 3 (2018), 217–227.