Virtual Rope Slider
Tatsuya Kodera†, Naoto Tani†, Jun Morita†, Naoya Maeda†, Kazuna Tsuboi†,
Motoko Kanegae†, Yukiko Shinozuka†, Sho Shimamura†, Kadoki Kubo†, Yusuke Nakayama†,
Jaejun Lee†, Maxime Pruneau†, Hideo Saito† and Maki Sugimoto††Graduate School of Science and Technology, Keio University, Yokohama, Japanvropeslider@imlab.ics.keio.ac.jp

ABSTRACTThis paper proposes "Virtual Rope Slider", which expands a ropesliding experience by stimulating sense of sight, hearing, windand vestibular sensation. A rope slide in a real world has physicalrestrictions in terms of scale and location whereas our "Virtual
Rope Slider" provides scale and location independent experiencesin the virtual environment. The user is able to perceive a different
sense of scale in the virtualized scenes by multi-modal stimulation
with physical simulation.

Categories and Subject Descriptors
I.3.7 [Information interfaces and presentation]: Multimedia
Information Systems – Artificial, augmented, and virtual realities

General Terms
Human Factors, Entertainment VR

Keywords
Rope Slider, Virtual Reality, Sense of Scale, Multi-modal
Stimulation

1. INTRODUCTION
A rope slide is one of the playground equipment for outdoor
exercise. Figure 1 shows a snapshot of rope slide. The player
holds on its rope and slides downwards along the cable. A rope
slide in the real world has physical restrictions in terms of scaleand location. For the restriction of the scale, the scale of a humanis constrained, so the user can enjoy it in a fixed scale factor. For
the restriction of the location, we can only play with it in a
specific environment. Our system: "Virtual Rope Slider" expands
the experience of rope-sliding in these two points by stimulatingsense of sight, hearing, wind and vestibular sensation. Figure 2
shows our "Virtual Rope Slider".

Figure 1. Rope Slidesystem changes the sense of scale by changing the eye position of
the user in the virtual world, where other factors (sound, wind andvestibular sensation) are constant.
The main contribution of our system is to provide virtual ropesliding experience in 3D reconstructed virtual environments. It is
possible to change the sense of scale in our dynamic environment
by manipulating factors of the virtual scene graph.

There are many studies on perceived size in static environments.
The perceived size of the virtual world can be controlled byinterpupillary distance of head mounted display (HMD) [1].
However, our system is in a dynamic environment so theperceived distance of sliding motion was not only affected byinterpupillary distance but also by the human-to-virtual-world
ratio. We reconstructed and created the virtualized real world
environments to measure the perceived distance of sliding. Our
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Figure 2. Virtual Rope Slider

Sliding down from thetop of the cable

Swinging back and stopping
Hitting the stopper at the end
Figure 3. Transition State of Real Rope Slide

2. RELATED WORKIn this section, we refer to the related works of motion platform
and perceived size in a virtual environment.
A motion platform is a mechanism that produces physicalmovement to provide stimulation of vestibular sensation. Usually,
the movements of the platforms are synchronized with a visualdisplay and multi-modal effects in virtual reality applications suchas video games, virtual simulation, and so on [2]. A combinationof these effects provides a sense of immersion into a virtualenvironment and enhances the experience of kinematic changes inposition, velocity and acceleration.
The researches in size perception have been explored in manyyears [3] [4] [1] [5] [6] [7]. Here we refer to three types of scalechange factors.
Visual effect is the most common way to stimulate the sense ofscale. Tilt Sift lens [3] and blur effect [4] are known as thephotographic techniques and effects. They create scenes as if theobjects look like miniature models. Yanagida et al. [1] mention
the perceived size is affected by interpupillary distance of HMD
with a stereoscopic display.
We can also change the perceived size by displayed human size.
S.A. Linkenauger et al. [5] propose the system which displays thelarger virtual paws and the target object so that the user canmeasure the size of the object by their body scale. V.D.Hoort et al.
mention that the scale of a human is a reference scale to measure
the size of the world.
Redirected walking system [7] changes the perceived scale bychanging the distance of motion in a dynamic environment. Evenif the user walks around in a small area in a real environment, itgives an experience as if the user walked around in a large-scale
virtual room. In this system, the user can control the scene by theirwalking, but in our system user's motion is controlled by themotion platform system.
Our system is a motion platform system which provides a varietyof sense of scale by changing parameters in a dynamic virtualenvironment.

3. A SENSE OF SCALE OF MOVEMENTIN DYNAMIC VIRTUAL ENVIRONMENTThe technology of VR allows us to reproduce a sense of reality inour daily life by providing essential stimulations for humanperception. By carefully changing the stimulations, it is possible
to give different reality beyond the physical restrictions. Our
system provides a variety of perceived scale by stimulating
sensations.
There are several remarkable studies to stimulate the sense ofscale in static environments as already discussed in section 2.
According to the related works, the following elements areconsidered to be effective to the perceived size in our system.
Interpupillary distanceEye position from the ground
Gravitational acceleration

However, our "Virtual Rope Slider" is based on a dynamic
environment. Our motivation is to accomplish the elements which
affects to the perceived distance of sliding in a dynamic virtualenvironment.

4. USER EXPERIENCE
Figure 3 shows a transition state of a real rope-slide. We
investigated the experience of a real rope-slide to design oursystem. There are two important factors; a sliding and swinging
sensation of the user’s body. To produce these two sensations, oursystem stimulates sense of sight, hearing, wind and vestibularsensation.
Scenery change is the most important sensation to stimulate.
When the user is passing by an object, it looks gradually larger as
he or she is approaching and looks smaller as going away from it.
It gives a sliding sensation. For body-based scaling, the user
measures the scale of the virtual world by comparing the object
and their body size.
Auditory stimulation is strongly relevant to rope sliding
experience. When a player is sliding down along the cable, he or
she can hear the sound of the pulley.
When passing by a sound source, it sounds lager as he or she
approaches and smaller as goes away from it. A sound of

MotorIron PipeStarting signal

ImagePC

Rope
HMD

HMD

Micro-controller

SensorInformation

Sound

Controlling

Headphones

Headphones

Pressure sensor
Hearing

Sitting
seats

Sight

FansWind

User

Wire
Vestibular sensation

controlling

Moving

Fan

Rope

Fan

Motor

Figure 5. Block Diagram

Figure 4. System Configuration
collision at the end of the experience is also one of the effects tomake the user notice his/her position in the virtual world.

5. SYSTEM
5.1 Configuration

The wind is an effective sensation to give a hint of the direction ofsliding to the user. If the user slides down, he or she feels wind in
front of him by air resistance. If the user reaches the end of theinclined cable and sliding back, he or she feels wind from theback.

The system configuration is shown in Figure 4.

The user feels the gravitational acceleration in sliding down by
stimulating vestibular sensation [8]. Furthermore, a sense ofswinging user's body is also the important vestibular sensation
when the user reaches the bottom of inclined cable.

A rope with a seat is hanging from the top of the iron pipe
structure. The rope is connected to a motor by a wire. The wire
can be wound up and paid out by the motor. Fans are placed on
the ground and emit a wind to the user. The user wears HMD(Oculus Rift [9]) and headphones, which both give stereoscopic
sensations.
Figure 5 shows a block diagram of our system. The camera
position of rendering is determined by the position of the user in a
virtual world and the camera pose is determined by the direction(a) Space(b) City

Figure 6. Computer Graphic Scenes(c) Toy Bricks
Figure 7. 3D Reconstructed Scenes(d) RoomFigure 8. Sequential Images of Virtual Rope Sliderof the user's head tracked by the acceleration sensor in Oculus Rift.

6. CONCLUSIONS

We use Unity [10] for physical simulation to calculate the speed
effect to the motor, fans, volume of the sound and camera position
and rotation.
We have seven computer graphic scenes (Figure 6) and two 3Dreconstructed real environments (Figure 7). Both should becreated in the off-line phase so that the rendering works on realtime.

This paper introduces our virtual rope sliding system in 3D
reconstructed real world and the system configuration to provide
the virtual sliding experience in our virtualized environment. We
stimulate sense of sight, hearing, wind and vestibular sensationand manipulate the sense of scale through the rope-slidingexperiences in virtualized real environment. This system allows uschange physical restrictions of scale and location. It provides a
new rope sliding experience in various scenes.

5.2 Physical Simulation

7. ACKNOWLEDGMENTS

As mentioned in section 5.1, speed is related to the control of themotor, fans, volume of the sound and camera position and rotation.
In this section, we refer to physical simulation of the sliding rope.
Figure 8 shows sequential images of the user experience.
Figure 9 shows the rope model in our virtual environment. Acamera for rendering is attached to the middle of the rope. As
sliding down along the cable, air resistance affects the verticalangle of the rope. Air resistance is high in high speed. When theresistance gets high, the power of the fan gets high and thevertical angle gets steep. Since the camera is attached to the rope,a direction of the camera is facing down and the seat of the slidegets steep.
When the rope reached to the end of the cable and collides with it,
it swings forward due to the moment of inertia as shown in Figure
9. The camera is facing to the ceiling and the angle of the seatchanges.

CameraCameraCameraWe are deeply thankful to the International Collegiate VirtualReality Contest (IVRC) 2013 and its community whose commentsand suggestions were innumerably valuable.

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StaticSliding down

SwingingFigure 9. Physical Simulation of the Rope and Camera Angle[8] Virre, E. Virtual reality and the vestibular apparatus.
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