WISS 2023

VR リダイレクションを用いたゴルフスイングトレーニングシステム
余 志皓 ∗

廖 振傑 ∗

小池 英樹 ∗

概要.
本論文は、ゴルフのトレーニングにおいて、スイング軌道を修正させるために、仮想現実（VR）
技術を用いたボール位置のリダイレクションを提案する。一連のスイング動作の中で、インパクト前にボールを前方に移動させることで、ゴルファーが無意識にボールの移動に反応し、スイング軌道を修正する。このリダイレクションを達成するために、仮想環境（VE）を開発し、高速光学トラッキングデバイスを使用
してゴルフクラブのモーションデータを収集し、リアルなシミュレーションを行った。本研究ではリダイレ
クションのためのボール移動パターンを 3 つ提案し、12 人の被験者を対象としてユーザ実験を行った。この実験により、異なるパターンのトレーニングをしたゴルファーの学習率を評価し、それぞれのパターンの効果を検証した。その結果、ボールの「間欠的な (Interspersedly)」移動が、ゴルファーに無意識にスイン
グ軌道を修正することができ、持続的な学習効果を示した。この手法をトレーニングに取り入れることにより、ユーザの偏ったフォームを改善し、技能レベルを向上させる可能性がある。

1

Introduction

For golf beginners, there is often a high degree of instability in the ball’s flying direction
when they strike it. This problem also happens to golfers with years of experience playing the round. They often perform a strong
bias in their swing path, particularly tend to deflect from outward to inward, causing the ball toveer left of the target. This outward-to-inward
path tendency often leads to a series of errors,
one of which is commonly known as a “slicing
shot”[1]. The slicing shot causes the ball to veer
sharply in the opposite direction (right side) andis a challenge for many golfers [8]. There arevarious reasons for this outward-to-inward bias,
most of which can be attributed to an erroneous
swing motion called the “over-the-top swing”.
Seeking guidance from a professional coach isarguably the most efficacious method to rectify
these swing inaccuracies. However, the associated costs might deter beginners, particularly
those pursuing golf as a mere pastime. A common alternative, self-practice, whether indoors
or outdoors, may risk ingraining poor techniquesin the absence of proper guidance.
This work proposes a virtual reality (VR) golf
training system to help golfers correct inappropriate habits during a swing. We use a spatial
distortion technique of VR to change the user’s
behavior, also called redirection, while the users∗

Copyright is held by the author(s).
東京工業大学

do not perceive the change of position. In the
VR system, we dynamically move the ball position when the users are performing a downswing. When the ball shifts a short distanceahead, the user promptly shifts his downswing
path forward, thus correcting his swing path tosome extent.
Based on previous research exploring the prolonged aftereffect of visuomotor adaptation togradually distorted reality in VR[7], we introduce three modes to shift the ball during thedownswing. To evaluate the effectiveness of the
proposed system, we develop a VR golf simulation system incorporating the three modes above
and conduct a user study.

2

RELATED WORK

2.1 Visual/Object redirection
Visual dominance[2][3] can be used to influence the user’s experience in the virtual environment and thus achieve specific desired effects,
with redirection techniques being one of the mostpopular. For example, in redirected walking [13],users may perceive themselves as walking in astraight line, although they are walking on a
curved path. A non-strict mapping between headrotation and orientation in the real and virtualworld achieves this work.
Kasuga et al.[7] had participants wear VR headsets and had them perform the task of repetitive
3D arm reaching for a target on a touchpad infront of them. The target had multiple movement modes. In the abrupt condition, the im-

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Fig.1. Make the ball shift forward by tracking the golf club while downswing, avoiding “over-the–top”-like motion that can cause outside-to-inside swing path.

ages were rotated by 20°, while in the gradualcondition, the rotation was increased stepwise
from 0° to 20°. Their results showed that the
decay of the aftereffect was slower in the case ofslow movement. This research motivated us todesign modes in which the user is unaware of theball’s movement. We hypothesize that this typeof mode could potentially help users to maintaintheir training results effectively.
2.2

Golf training in HCIThe application of technology in golf training
mainly includes the use of AR [4], VR [9], projection systems [14][5][6], and monitors to aid users
to train through various visualizations. Other
approaches involve incorporating forms of feedback, such as auditory cues [14][6], haptic feedback achieved by modifying golf clubs [10][11], or
external haptic feedback devices [15]. Moreover,research that helps users train by deep learning
the swings of skilled players has been actively
researched in recent years [12].
In a series of research [14][5][6] focusing on
the use of the so-called “Virtual Golf Shadow”
for golf training, a skilled golfer’s silhouette captured through motion capture technology is projected onto an indoor golf training course. Users
can learn and improve their golf swing in realtime by consciously aligning their silhouette withthe skilled golfer’s. However, this study is only
applicable to beginners who need to start learning from posture. Moreover, habits such as “overthe-top swing”, caused by many personal preferences and details, are challenging to correct
simply by differentiating from experts. Our approach can be used not only for beginners topractice but also for experienced users to correct
the swing path.

Fig.2. Left: The user takes the HMD for a realswing. Right: the user interface in VR.

3

Design and implementation

The system design is shown in Fig.1. To get
accurate motion tracking, we use a high-precision
motion capture system (OptiTrack) to track thegolf clubs and simulate the outcome of the ballbeing hit in VR in real time. Finally, we developed three different golf ball shift modes fortraining using the VR golf setting.
3.1 User interface in VR
The user interface in VR is shown in Fig.2.
The user must stand on the yellow line and swing,with the red flag as a target on the user’s leftside.
According to golf rules, a golf ball’s diametershould not be less than 42.7mm. Hence, the diameter of our model ball is set to 43mm. To
make it easier for beginners to hit the ball, we
let the ball model’s collision body diameter beVR リダイレクションを用いたゴルフスイングトレーニングシステム

Fig.4. The procedure of user study: Mode
1, Mode 2, and Mode 3 represent the 3modes in a randomized order.
Fig.3. Ball shift sketch for Abruptly and Gradually modes.

1.6 times larger than itself, which is 68mm.
In the VR system, when the user hits the ballwith a certain force, the ball flies slightly higher
than in reality, while the speed in the x and z
directions remains the same as in reality. Our
research focuses on the swing path rather than
the angle of the golf club face, which allows theuser to observe the ball’s flight trajectory morecomprehensively. The ball’s flight trajectory disappears after the ball hits the grass, while a newball subsequently appears on the ball spawner
for the user to continue training.
3.2 Shift of the ball
We developed three shifting modes in which
the ball shifts the same distance. The distanceof the ball movement is two times the diameter of the ball model, 86mm. The previous
study by Kasuga et al.[7] mentioned four modes:
abrupt condition, gradual condition, a mixtureof abrupt condition and baseline, and a mixture of gradual condition and baseline. Amongthem, gradual condition and the mixture of gradual condition and baseline are the most effective,
with a slower decay of after-effects. In contrast,
the mixture of abrupt conditions and baseline
mode has the worst effect. To verify whether
abrupt and gradual conditions produced similar
results in our study, we implemented “Abruptly”,“Gradually”, and the “Interspersedly” modes forthe user study.
Abruptly (A) In this mode, when the user ispreparing to hit the ball, the ball suddenly shifts
towards the front for a distance (Fig.3 Left).
Gradually (G) This mode makes the ball shiftslowly towards the front for a distance and tries
not to be noticed by the user. To achieve this, wetake advantage of the feature of the tile textureof grass by having the texture move forward withthe ball such that the user would lose their frameof reference and be as unaware of the ball’s shift
as possible(Fig.3 Right).
Interspersedly (I) This mode alternates between the G mode and the non-shift mode. We
aim to correct the user’s habit with the G modeswing while preventing over-correction with the“non-shift” mode, allowing the user to learn andverify between the two modes.

4

User Study

To test and verify the hypothesis that shifting
the ball during the swing can improve the user’s
swing path, we conducted a user study involving
12 participants.
4.1 Design and procedure
We first give instructions to the participants
on how to swing the golf club properly by having
them practice on a real-world indoor golf course.
As done in actual training and golfing, we asked
the participants to aim at the ball and keep theireyes on it throughout the swing. After we ensure
they are familiar with the basic swing by completing a full swing 5 times, we let them train
with VR headsets and try to hit the ball in VR.
We have all participants use a #7 Iron club, stayin a line throughout the test, and the participant
can see the ball’s flight path. When the participants hit the ball four times continuously in VR,
and it lands in the range of -30 °to 30 °, we consider that they are ready to train in VR. Then,we give instructions to the user about the experiment, including matters such as the purpose of
the study and the three different modes.
During the experiment, we had each participant test all three modes randomly. Before testing the three modes, the user performed 12 swings
in the non-shift mode as the baseline. As shownin Fig.4, for the three different modes, such as A
mode, we let the user perform 36 swings in the

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A mode, followed by 12 swings again in the nonshift mode. We mainly use the last 12 swings toevaluate the effective learning rate. Particularly,
in the I mode, participants first performed 6
swings in non-shift mode, followed by 6 swings in
the G mode. The participants repeat these twomodes until they complete 36 swings and thenperform the final 12 swings in the non-shift modefor evaluation. The training is approximately
10 minutes for 48 swings in each condition. We
asked the participants to take a 10-minute break
between conditions while filling out a questionnaire about this part of the experiment. The
whole experiment lasts approximately one hour.
4.2 Participants
We invited a total of 12 participants (minage =20, maxage = 31, meanage = 24.25, sdage =3.16). Eight of them were men, and four were
women. Three had no knowledge of golf, six had
some knowledge of golf, they may have watchedgolf videos or practiced swings, and the otherthree had some golf experience, they frequently
engage in indoor golf training or have practicalexperience playing golf games. Four of themused VR regularly, five of them had VR experience, and three of them had no VR experienceat all.
4.3 Questionnaire
We used a customized questionnaire to evaluate the participant’s subjective experiences ineach mode, which served to support the discussion of the result. We presented four questions
for each mode using a 5-point Likert scale questionnaire:• Q1: How about your experience of thiscondition?
• Q2: Can you feel the ball shifting when
you swing?
• Q3: Do you think the shift of the ball disturbed you?
• Q4: Do you think your swing form changed?

5

Results

5.1 Velocity bias
In our VR environment, the −x direction represents the inward, the +x direction represents
the outward, and the +z direction represents thecorrect direction, i.e., the center(Fig.2). If the xcomponent of the club velocity is negative, thehit will cause the ball to fly to the left and viceversa to the right.
vx /vz represents the offset value of the velocity
acting on the ball concerning vx , which we callthe velocity bias. arctan(vx /vz ) represents theoffset of the velocity in degrees. When vx /vz =0.1, it represents an offset of 5.71°, and 0.2 represents an offset of 11.3°. If vx /vz is negative,
the swing path swings outward to inward andvice versa. If all other factors are accurate, thenvx /vz will represent the final deflection of theball. We want to see a smaller absolute valueof velocity bias during training than during theinitial measurement. More importantly, we want
the absolute value of velocity bias to be as small
as possible after training, representing a significant training effect in the normal mode even after training.
We first conducted a two-way repeated-measure
ANOVA with turn and mode as variables for thethree modes(normally distributed and satisfies
the spherical assumption). The results showedthat for the three modes, both turn(df = 47,f =
1.93,p < 0.001) and vx /vz (df = 2,f = 39.10,p <0.001) or the interaction between turn and vx /vz(df = 94,f = 1.40,p < 0.01) have significantly
differences. We then performed a Tukey-Kramer
posthoc test on the three models and found significant differences between (A, I) and (G, I)
in all three models (both p < 0.05). No significant difference occurred between A mode and G
mode(p = 0.09 > 0.05).
5.2 Average velocity bias
Using the data from the 12 times non-shiftmode swing at the beginning, we found that 9 of
the 12 participants(P1, P2, P3, P4, P5, P6, P7,
P9, P12) were habitually biased from outward
to inward, two participants(P10, P11) were between inward and outward, one participant(P8)was habitually biased from inward to outward.
Because our ideal target is who is used to playing from the outward bias toward the in-ward, we
first averaged the data of these nine participants
individually, as shown in Fig.5. From the average data, the velocity bias (vx /vz ) of these nine
participants in the first 12 shots ranged between−0.2 and −0.1, which means that on average,
each swing would have a bias of approximately
9°from outward to inward.
We analyze the distribution of velocity bias

VR リダイレクションを用いたゴルフスイングトレーニングシステム

Fig.6. Questionnaire on a 5-point Likert scale
for participants’ experiences, perceptionof ball movement, discomfort, and conscious alteration of the downswing pathfor each mode.

Fig.5. The average Velocity Bias of the 9 out of
12 participants who have a habit of swinging from the outside to the inside.

for the first 36 times in all three modes. In the
A mode, the values were the largest among thethree modes most of the time, and the velocity
bias was between 0.05 and 0.15 mostly, meaning that the swing path was from inward to outward. In the G mode, the velocity bias fluctuated around 0.05, meaning that the average bias
angle was close to 3 degrees, and the bias towards
either side was not very strong. Intriguing results exist in the I mode because it is performed
in a cycle of six times in the non-shift mode andsix times in the G mode. The results of the first36 times are distributed in positive and negativesides with six as the number of cycles. However,
we can observe an overall tendency to converge
to 0, and the velocity bias is already close to 0
in the 30th to 36th times in the G mode.
5.3 Questionnaire evaluation
11 out of 12 participants thought it was easier to hit a golf ball in VR than in reality, andone thought it was about the same difficulty.
Nine people thought golf training using VR was
reliable and preferred practicing in a VR environment. The questionnaire results for eachmode are depicted in Fig. 6. In terms of theoverall experience, G (M = 4.25, sd = 0.72)
and I (M = 4, sd = 0.91) were better than A(M = 3.42, sd = 1.03). The majority of participants noticed the movement of the ball in the
A mode (M = 1.5, sd = 0.76), whereas in the
G (M = 3.92, sd = 1.26) and I (M = 3.58,
sd = 1.1) modes, users did not perceive the ball’s
movement frequently. Additionally, users felt

more disrupted and found it more challenging tohit the ball in the A mode, requiring a conscious
effort to modify their downswing path. After
conducting all three modes and understanding
the purpose of our user study, the majority ofparticipants said they preferred the I mode fortraining.

6

Discussion

6.1 Main ﬁndings
From the velocity bias, it can be found that all
three modes have shown positive effects during
the training. A and G modes showed the mostsignificant change. Due to its cyclical nature, theI mode experiences fluctuations over time, but
gradually approaches zero. This result is further supported by the questionnaire responses.
The questionnaire results indicate users were notaware of the shift of the ball in the G and I
modes. Therefore, users reported slight discomfort only in the A mode due to the instantaneous
shift of the ball, which made it challenging to
make accurate hits.
After 36 swings of training, the velocity bias in
the A mode regressed to the baseline level. The
G mode and I mode maintained the training effects in the short term and showed similar levels.
(RQ 4 is true) The questionnaire also supported
the superior overall performance of the I mode.
We believe this is because users can make nondeliberate swing path corrections during training
in the I mode, which allows the user to validate

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and learn.
6.2

Subjective Feedback

Some participants thought that for golf beginners, training directly with a real ball is challenging to hit and not safe enough. “I like that
there was no danger of having to pick up theball or risk a flying ball.”(P6) Hence, golf training using VR is appropriate for beginners. VR
golf can help beginners get up to speed rapidly
and is very motivating. “It’s exciting that you
could hit the ball constantly without catching
the ball.”(P4) Furthermore, visualizing the ball’s
trajectory, where it lands, and other informationin VR can be very beneficial for regular indoor
golf training. “ it is really fun that I can hit theball and can see the trajectory of the ball.”(P7)“I firstly touch the golf club, but I really enjoyed
the golf training in all section, because I can hit
the ball. It is useful to beginners to the training
to motivate them.”(P12)
For perceptions of ball shift in different modes.
P6 mentioned:“In the A mode, the ball positionchanged so significantly that I felt I needed toconsciously adjust my posture. There wasn’tmuch difference between the G and I modes
because I didn’t even notice the change in ballposition.” P12 commented:“I occasionally feela sense of space being stretched in the G and
I modes, but despite this, I don’t consciously
wonder if this is the ball shifting because thedownswing is really fast.”
Other comments were concerned with correction, i.e., what was originally an outside-in trend
but was corrected to an inside-out trend. Under the distance when we set the ball to shift,
the learning result of the A mode was not effectively retained, and the over-correction phenomenon occurred under the G mode. At thesame time, the I mode can be contracted to amore reasonable interval by the user’s verification during training. However, for user trends
that are not outside-in or more exaggerated, it
is unsuitable to train directly at this direction
and distance of ball shift.
6.3

might cause poor bias guidance when using our
method.

Limitations and future work

Several participants also indicated that evenin the G and I modes, they were still distracted
by the ball’s movement. In our user study, 1of the 12 participants had no significant swing
bias, and 2 had an inward-to-outward bias, which

Omnidirectional Redirection For different deflections, including inward-to-outward or outwardto-inward, other users may have different deflections when hitting the ball. Each user has adifferent bias; therefore, fixed ball shift distanceand direction do not suit everyone. We plan todevelop an adaptive training system that constantly adjusts to each user’s bias. This will
not only help users with a significant bias tostandardize their swing path but also help users
with a smaller bias each time to reduce their bias
trend.
Spatial Distortion of Angles Using object
position redirection to correct the downswing path
may somewhat change the overall swing plane.
Our evaluation is mainly based on velocity bias,
i.e., angles, so we plan to use spatial distortionof angles as well to allow users to learn unconsciously. We plan to use virtual arrows on the
ground to indicate the direction of the user’s
swing while gradually changing the direction of
the arrows during the swing process. This may
result in better correction with less discomfort.

7

Conclusion

In this work, we developed a VR method tohelp users correct their swing path by shifting
and redirecting golf balls. We proposed threeball-shifting modes and conducted a user study
to compare the advantages and disadvantages of
the three modes. Subsequently, we analyzed thethree modes’ learning rate by visualizing the golf
club’s speed and swing path during and after
the training sessions. Our findings revealed thattraining with the I mode, involving golf ball redirection, was particularly effective in helping individuals with an outward-to-inward swing bias
standardize their swing path. In the future, weplan to enhance the system by incorporating otherfeedback mechanisms and omnidirectional adaptive redirection and conduct further studies onother motor skill training. These future improvements aim to provide many users with further
assistance and immersive training experiences.

謝辞
本研究は JST CREST JPMJCR17A3 の支援を受けている.

VR リダイレクションを用いたゴルフスイングトレーニングシステム

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