Elevate: A Walkable Pin-Array for Large Shape-Changing
Terrains
Seungwoo Je1 , Hyunseung Lim1 , Kongpyung Moon1 , Shan-Yuan Teng2 , Jas Brooks2 , Pedro Lopes2 ,Andrea Bianchi1
Industrial Design KAIST1 , Computer Science University of Chicago2{seungwoo_je;charlie9807;jkpmoon;andrea}@kaist.ac.kr,{tengshanyuan;jasbrooks;pedrolopes}@uchicago.edu

ABSTRACT
Current head-mounted displays enable users to explore virtualworlds by simply walking through them (i.e., real-walking VR). This
led researchers to create haptic displays that can also simulate different types of elevation shapes. However, existing shape-changing
floors are limited by their tabletop scale or the coarse resolution of
the terrains they can display due to the limited number of actuatorsand low vertical resolution. To tackle this challenge, we introduce
Elevate, a dynamic and walkable pin-array floor on which users canexperience not only large variations in shapes but also the detailsof the underlying terrain. Our system achieves this by packing 1200
pins arranged on a 1.80 × 0.60m platform, in which each pin canbe actuated to one of ten height levels (resolution: 15mm/level). To
demonstrate its applicability, we present our haptic floor combinedwith four walkable applications and a user study that reported
increased realism and enjoyment.

CCS CONCEPTS• Human-centered computing → Haptic devices.

Figure 1: Elevate is a walkable high-resolution and largescale pin-array display that can generate a variety of physical terrains for virtual reality. Here, we demonstrate our device generating the terrain of a landscape and a user walking
on it.

KEYWORDS
Haptic Floor, Shape Changing Display, VR
ACM Reference Format:
Seungwoo Je1 , Hyunseung Lim1 , Kongpyung Moon1 , Shan-Yuan Teng2 ,Jas Brooks2 , Pedro Lopes2 , Andrea Bianchi1 . 2021. Elevate: A Walkable
Pin-Array for Large Shape-Changing Terrains. In CHI Conference on Human
Factors in Computing Systems (CHI ’21), May 8–13, 2021, Yokohama, Japan.
ACM, New York, NY, USA, 11 pages. https://doi.org/10.1145/3411764.3445454

1

INTRODUCTION

Today, the majority of head-mounted displays, even most commercial devices, allow users to explore virtual worlds by simply
walking around in their surroundings; this is known as real-walking
Virtual Reality (VR). The advantage of real-walking VR as a locomotion modality is that it is immersive as it stimulates the user’s
proprioceptive and vestibular senses as users physically move theirbodies both in the real and virtual environments. This compelledresearchers into tackling a subsequent key challenge that arises
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https://doi.org/10.1145/3411764.3445454

in real-walking VR systems: not only should users be able to walkaround but also they should be able to feel the terrain beneath theirfeet (e.g.,[18, 23, 27] ).
In fact, although often taken for granted, walking is a rich somatosensory activity, all the way down from limb movements tothe feedback we feel from the soles of our feet. The body is capable of perceiving the slightest variation in inclination, bumps,
and holes in the terrain, with the feet serving simultaneously askinesthetic [23] and tactile [44] sensors. Different from the hands,
the static and dynamic forces applied to the feet during standing or
walking are in the order of hundreds or thousands of Newtons [44],making the experience of "feeling through the feet" a unique yet
powerful haptic experience.
The search for this elusive haptics for feet, led researchers into
engineering haptic devices that can render terrains by physicallydisplacing modular pieces that the user stands on, such as moving
robot tiles [10], tilting haptic tiles [1, 2, 5], inflatable airbags [36, 40],
tilt-adjustable treadmills [24], and pin-arrays [33]. However, theseprevious shape-changing floors are limited by their tabletop scale [1,2, 5] or the coarse resolution of the terrains they can display, due
to the limited number of actuators [2, 10, 24, 33, 36, 40] and their
low vertical resolution [2, 24, 40].
To tackle these challenges altogether and contribute to the fieldof interactive haptics, we introduce Elevate, a dynamic and walkable pin array floor on which users can not only experience large

CHI ’21, May 8–13, 2021, Yokohama, Japanvariations in shapes but also subtle details of the underlying terrain, as depicted in Figure 1. Our device achieves this by means of1200 individually controllable pins arranged on a 1.80m × 0.60m
platform. Furthermore, each 3cm × 3cm size pin can be actuated to
one of ten height levels (resolution: 15mm/level). To illustrate thedesign space enabled by this one-of-a-kind large-scale haptic floor,
we present it in combination with several real-walking VR andstandalone applications. Lastly, we validated our prototype througha user study in VR, in which participants reported increased realism and enjoyment when experiencing the VR environment via
Elevate.

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Seungwoo Je, et al.

segment of the whole floor, typically in a grid layout), such as bymanipulating the tile’s adjustable slope [2, 5], using a turntablewith a slanting mechanism [1], or even using adjustable incline
treadmills [8, 9]. For example, the Ground Surface Simulator [24]is a treadmill featuring six linear actuators that together create
various slopes on which the user can walk on. However, in thesetypes of haptic devices, the expressiveness of terrain detail felt by
the feet is limited as their resolutions are very coarse, i.e., each tile
is very large. Elevate, on the other hand, renders both the topology
of a landscape and its non-linear slope while intentionally avoiding
user’s instrumentation which causes discomfort to the users.

RELATED WORKThe work we present in our paper builds on the fields of haptics,
especially on hardware-techniques that deliver haptics to the user’s
feet, not only for virtual-reality but also for more general interactive
walking experiences.

2.1

Foot-based Haptics

Kinesthetic and tactile feedback through one’s feet, such as elicitedwhen walking [23, 44] in virtual reality, is an important factor
for attaining immersion in virtual environments or creating richinteractive experiences. To achieve this, researchers have developed
a number of wearable devices that deliver foot haptic feedback to
the user’s feet. One such approach is to create "haptic shoes", i.e.,
shoe-like interfaces, embedded with haptic actuators, that users
wear as they walk around. For instance, Turchet et al. [41] andTakeuchi [38] attached vibration actuators on the sole of the shoes
to provide a walking experience on virtual ground. Hill et al.[7]also explored transferring information by using vibration actuators.
RealWalk [32] adopted actuated MR fluid to express the deformationof materials on the ground in VR, such as snow, sand and mud. Wanget al. [46] developed air-bladder-based elastomeric shoes to express
the slope of the ground. Level-Ups [28] is a pair of mechanicalbrake-actuated shoes that can simulate different heights of a virtual
terrain. Although wearable foot haptic devices have the benefit
of working over a larger (potentially infinite) area, they require
instrumenting the user’s feet, which results in reduced comfort.
Another well-researched approach for delivering haptics to theuser’s feet is to let users stand on a platform embedded with haptic
feedback. Visell et al. [42, 43] used vibrators and spring mechanisms [44] to provide the feeling of walking over snow or sand, i.e.,achieving ground textures. Wohlauf et al. [47] introduced the haptic
tile, which works as a weight scale on which users have a senseof load with rigidity instead of the numeric weight value. Also,
researchers have explored adding tangible objects, which the users
can kick around to control their interface, on top of interactive
floors [29].
Haptic floors are of especial importance for real-walking VR
because, in this type of setups, the user is already bounded tothe tracking volume and thus the aforementioned advantages of
haptic shoes become less pronounced. As such, researchers havelong explored robotic walking simulators [11, 30] and robot tiles,
which can move up/down, allowing users to walk over different
heights. The more recent approach, is to directly manipulate theterrain by employing motor-actuated tiles (i.e., a tile is a modular

2.2

Pin-array Displays

Shape displays [6, 12, 14–16, 25, 31, 37, 50, 51] provide a higher
resolution implementation of the aforementioned actuated-"tiled"approach, allowing to display physical 2.5D shapes with high resolution. However, most shape displays are designed as a tabletop
interface for interactions with the hands and arms [6, 15, 16, 31,
37, 50, 51]. These shape displays are often implemented via a 2D
array of pin actuators, with each pin being moved independently
by a motor, typically a linear actuator as in [6, 15, 16, 31, 37, 50].
The result is high resolution with, typically, fast update speeds.
However, the limiting factor is that these linear actuators cannot
withstand hundreds of kilograms of force, i.e., users can touch themwith their hands but cannot stand or walk on them.
Our device takes inspiration from these aforementioned pinbased shape-changing tabletops but aims at redesigning their innerworkings to enable foot-based haptic feedback, aiming for a large
scale device that covers a sufficient arena and withstands a user’s
weight as they walk on the device.
In fact, other researchers have recently explored the idea ofgenerating different terrains using push-pull mechanisms, such as
pneumatic actuators [36, 40], or mechanical linear actuators [2, 24,33] installed on a platform. For instance, both TilePoP [40] andLiftTiles [36] are haptic floors that use pneumatic actuators as an
approach to scale up in one dimension to display virtual objects.
Yet, these platforms are of coarse resolution, and inflated actuators
are not stable enough for any user to walk on, as researchers havehighlighted in their findings [36, 40]. Moreover, researchers havebuilt haptic floors that generate terrains, such as the ALF (ALive
Floor) [33]. ALF has 28 pin actuators with eight triangulated panels
on each actuator. However, this device, much like those of [40]and [36], is limited to low-resolution feedback, not quite capableof generating terrains with high-resolution, e.g., they can elevatethe user’s feet but cannot generate a sharp incline or the feelingof standing on textures and uneven ground (i.e., rocky ground).
Instead, Elevate bridges between these trade-offs, by proposing awalkable large-scale and high-resolution shape changing pin-array
display that can render a variety of physical terrains with a finite
number of actuators.

Elevate: A Walkable Pin-Array for Large Shape-Changing Terrains

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FOUR KEY CHARACTERISTICS OF HOWELEVATE CREATES WALKABLE DYNAMICTERRAINSTo give the reader a complete picture of how Elevate creates walkable dynamic terrains, we describe an example walkthrough of auser experiencing a rocky desert in virtual reality (VR).
As shown in Figure 2, the user is crossing a rocky VR desert,
but the path is cut off by a canyon. To cross over the canyon, theuser picks up some nearby rocks and drops them into the canyon.
After throwing enough rocks, these start to pile up into a pillar thatstands out. As a response, Elevate creates a physical pillar by moving
its pins upwards. Because the elevation created by our device isstable, due to its strong locking mechanism, the user can cross thecanyon by physically stepping on the pillars. This depicts two amongfour key characteristics of our design: (1) it withstands humanweights; and, (2) its feedback is dynamic, i.e., it can re-configure
any pin that the user is not standing on at run-time.

Figure 2: As the user fills the bottom of the cliff with rocks,
Elevate dynamically creates pillars that match the shape ofthe rocks. These pillars are sturdy enough that the user canwalk on them to cross the canyon.
Then, on the other side of the canyon, the user encounters arocky fields for which is finding a way through is difficult. As theuser keeps walking (Figure 3 (a)), the user is able to feel the terrain
underneath. This showcases Elevate’s third key characteristic: (3)its a large walkable surface of 1.8 x 0.6 m, longer and wider than
the typical haptic floor [2, 5], and compatible with the exploredsurface area used for VR applications [33].
Finally, the user finds a way out of the desert by stepping over
several rocks of different shapes and sizes, which our device generates accordingly as depicted in Figure 3 (b)– the user feels eachrock’s shape and size at each step. This is only possible due toour fourth key principle: (4) unprecedented resolution of 1,200
pins, each covering an area of 3 x 3 cm in a 20 x 60 grid. Our
pins can also rise up to 15mm, with 10 discrete intermediate positions (15 mm vertical resolution). This level of detail, seen before
only on tabletop pin-array displays [6, 15, 16], is what allows to
depict the fine-grained differences between the rocks displayed in
Figure 3 (c-f).
In summary, compared to previous haptic floors, Elevate provides unique physical affordances that allow to realize new andunforeseen applications at a larger scale. While we demonstrated
the four benefits of Elevate (i.e., withstands human weight, dynamic, large scale, and high-resolution) in the example of this VR
walkthrough, in the Applications section we will also showcase
how Elevate enables new interactive scenarios outside of VR.

Figure 3: (a) As the user keeps walking in this VR desert, thefeet keep experiencing tactile feedback over a haptic largearea of 1.8 x 0.6 m; (b) Here, the user feels the shape of a rockunder the feet. (c-f) Elevate makes use of its high verticaland horizontal resolution to render the different shapes ofthe different rocks the user steps on.

4

SYSTEM IMPLEMENTATION

Elevate is made of three components: 1200 pins, a shape generator(the electromechanical device that moves the pins), and a locking
system (the electromechanical device that secures the pins in place)(Figure 4). Generally speaking, the mechanical principle behind
Elevate is as follows: (1) its pins are actuated by the motorizedshape generator one row at a time, allowing them to take the shapeof the intended terrain; (2) what keeps the pins from falling backdown are strong magnets that temporarily hold the pins in place
at a desired height while a single row is being rendered; (3) then,when a particular row is updated (i.e., all pins of this row have been
set at their intended height), the pins are firmly locked using our
motorized brake mechanism; lastly, (4) after locking any row of pin,the user can walk over these.

Figure 4: Three major components of Elevate: (1) the pins(top); (2) its locking system (middle), and (3) its shape generator (lower). We depict also a detail of how we layered thematerials in Elevate’s mid supporting structure.
Elevate is mounted on a box-framed structure made from aluminium profiles (120 cm wide x 248 cm deep x 73 cm high). The top
side of the box (at 73 cm) is our actuated platform, and it is coveredby a smooth sheet of birch plywood (15T), which houses the pins
and prevents them from colliding with each other. In the middle,
there is a layered structure made of an acrylic sheet (6T) and of aniron plate (14T) glued together. All these elements combined makeup for a strong platform that bears the weight of an average user.
Furthermore, the side of the box structure also has attachmentsfor protective railings that prevent users from falling down from the

CHI ’21, May 8–13, 2021, Yokohama, Japan

Seungwoo Je, et al.

Figure 5: Hardware components of the shape generating system: overview of shape generator (left); hardware components ofthe custom actuator module (right).
platform. The following subsections describe the implementation
details of the three main components of Elevate and how they
communicate with each other.

4.1

Pins

Each of the 1200 pins of Elevate was machined from a block of birch
plywood and shaped to support a 150 mm vertical displacement.
The cuboid shape of the pins was designed by referring to previous
studies [6, 15, 16] and taking into account two requirements: density(no hole between the pins) and the need to operate the pins line byline (using the shape generator). The pin mainly consists of threeparts. The top part of the pin is a solid block of 195 mm with a 30 mm
× 30 mm section that can protrude from the platform. This is thepart of the pin that has to support the user’s weight and therefore
is completely filled to avoid deformations from compression. The
lower part is a comb-shape section with 24 notches. Half of these
are larger and are used in combination with the locking system —specifically, an aluminium bar that prevents vertical translations(see detailed explanation in locking system). These large notches
have a pitch of 15 mm, resulting in the pin’s vertical resolutionof 150 mm. The remaining notches are smaller and contains 12
permanent neodymium magnets (15 mm × 10 mm × 4 mm, ofstrength 3100 G) which are used to temporarily keep the pin liftedin the desired height level before the locks are inserted into thenotches. Finally, the bottom side of the pin is fixed with a metal ironplate (18 mm × 19 mm × 4 mm) which protects the pin from impacts
with the shape generator, and serves a magnetizable surface forpulling the pin down. In total, the system contains 1200 wooden
pins with 14,400 magnets and 1200 metal plates, for a cumulative
weight of 240 Kg (200 g per pin).

4.2

Shape generator

The shape generator is the core of the system. Its purpose is toindividually push or pull each of the 1200 pins, rendering various
types of terrains and features. The main challenge is to minimize
the number of actuators needed to individually control the heightof each of the pins. We achieve this by using a shape generator
that moves row by row on a rail underneath the pins platform, andpushes or pulls at the same time all the pins on the same row.

Figure 6: One of Elevate’s pins. Note the different parts thatcomprise its mechanics, from left to right: (1) a display part,which extrudes out of the platform; (2) a comb-shaped partwith notches that lock; (3) an iron plate at its base.

The horizontal movement is generated using a pair of aluminum
timing belts (GT2, 36 teeth, 6 mm) attached to a system of pulleys.
Pulleys are driven by two coaxial stepper motors (A15K-S545-G10
with 0.75 A/Phase) using a set of micro-stepper drivers (MD5-HD14)
and powered by a single 24 V power supply at 4.5 A. A switch isplaced at one end of the platform for homing and calibration. Finally,
all parts were attached to the main frame using 3D clamps madeof PolyLactic Acid (PLA). With this configuration we achieve a
horizontal resolution of 0.6 mm/step and a maximum operating
speed of 27.3 mm/s.
Our shape generator is a motorized device that moves the pinsin their vertical axis (up/down). It contains 10 custom push-pull
modules, each able to simultaneously drive two pins (Figure 5). All
10 modules are mounted adjacent to each other on an acrylic platform attached to the moving rail and can therefore simultaneously
actuate all the 20 pins of a single row. The pushing is achieved
via a rack and pinion mechanism paired with reduction geared
DC motors (IG30-MM8.6W-E, 12 V, 800 mA). Vertical positioning
works by placing 12 small neodymium magnets (ø2 x 1 T) inside
the rack at distances of 1.5cm, sensed by a Hall sensor (WSH138XPAN2) to close the loop. Conversely, the pulling mechanism was
implemented using an electromagnet (25 N pulling force at 12 V,
260 mA) placed on the top of the the rack. When the electromagnet
is in contact with the the bottom part of the pin (where the ironplate is attached), it turns on and the DC motor drives back therack downward. All electronic parts of each module (5V regulator,
H-bridges, LEDs, home switch, and an Arduino Nano) are solderedon a custom printed circuit board and powered by a five parallel
power supplies (LRS-350-12, 12 V, 145 A).

Elevate: A Walkable Pin-Array for Large Shape-Changing Terrains

CHI ’21, May 8–13, 2021, Yokohama, Japan

Figure 7: Overview of the software implementation used to control Elevate from a variety of different applications.

4.3

Locking System

The purpose of our locking system is to firmly secure the pins at a
specific height, so as to form the desired shape of the terrain and also
to allow users to walk over the resulting terrain. The main challenge
is the large number of pins, all of which require to be locked. To
address this, we built a modular locking mechanism that can handle
80 pins (four rows) with just two servomotors (HS-311 with 5 V,
650 mA) and four aluminum pipes (800 mm, ø5). The system works
by simultaneously sliding one pipe into the notches of all the pins
placed along the same row, effectively locking these and preventing
any vertical translation (Figure 8). To simplify our resulting device,
we used two servomotors to drive simultaneously four pipes, hence
simultaneously locking/unlocking four rows at a time. To cover all
the 60 rows of Elevate, we replicated the aforementioned locking
system 15 times along the longitudinal axis of the platform.

Figure 8: The locking module (a), pins are released (b), pins
are locked (c).
More specifically, our locking mechanism is driven by a rackand pinion, with a pair of spur-gears mounted on the shafts of the
motors, and a linear gear serving as a rack, which connects the fourpipes together. This allows for a 10mm displacement, sufficient forlocking and unlocking all pins in a row. All parts were 3D printed
using PLA. The locking system is controlled using an Arduino

UNO and two servo drivers (PCA9685), and communicates withthe computer via serial. A 5 V power supply (LRS-100-5, max 18 A)
was used to provide sufficient wattage for all the motors.

4.4

Software Control

Elevate is controlled by the interactive application software, typically running on a desktop computer (e.g., for VR, etc). Our software
operates at three distinct layers: application, communication, andfirmware. This hierarchical structure, which is depicted in Figure 7,
provides an abstraction that allows for reusing parts of the system,
and for decoupling the development of hardware and software.
The application layer is responsible of generating a 20 by 60
map containing the height position of each individual pin. This map
is then internally stored as a JSON object, ready to be transmitted
to the hardware. The details of the map-generation process areapplication-dependent and are described in the Applications section.
Applications can be written in any language or with any software
platform as long as they can create a JSON file — for example, we
describe VR applications that were built using C# with Unity3D,
and a mini-golf authoring tool that was built using Javascript andruns in a browser.
The communication layer is responsible of timing and dispatching the instructions to the hardware’s individual parts (shape
generator and locking system). All maps from the application layers are stored in a queue, and rendered as soon as the hardware
is available. Maps can be added to the queue, or can replace thosealready in the queue. Once the hardware is ready to receive commands, the software creates a series of instructions describing how
to actuate the 10 modules of the shape generator (a single row).
Each instruction consists of a JSON string with the numerical IDof the target module and the height of its two pins. Specifically,
it contains both the current and target positions of the pins, fromwhich the firmware software can compute the difference of how

CHI ’21, May 8–13, 2021, Yokohama, Japanmuch to push or pull. These JSON packets are transmitted overserial to the hardware.
Specifically, the communication layer is responsible for instructing the shape generator when and where to move (i.e., it follows thedisk scheduling algorithm [39]), when to unlock the pins, when/how
much to push or pull, and when to lock the pins again. These components of our software are structured as a closed-loop, as horizontal movements are restrained until all the racks on the actuator
modules are down and click the homing switch (Figure 5, right).
Furthermore, the controlling software internally keeps track of thecurrent configuration of pins (e.g., the previous map), and instructs
the hardware to skip rows that do not require changes, resulting insaved time.
Down at the hardware, our communication layer provides a
serial channel between a PC and the Arduino Uno that manages thelocking system. Furthermore we included a second serial channel
between the PC and an Arduino Mega, which communicates with
two Complex Programmable Logic Devices (CPLD, a device akin to
an FPGA) on the shape generator. Our first CPLD serves as a signal
multiplexer: it takes as input one transmission line and duplicates
it for each of the the 10 receiving modules. Meanwhile, our second
CPLD acting as an auditing node, collects the signal from all twenty
switches at the actuator modules and checks for successful homingof the actuators. The CPLDs (using an Altera EPM3064ALC44-10)
were programmed in Verilog.
On the lowest hardware level, the firmware layer consists of
the individual programs that run on each microcontroller, all together controlling the horizontal moving platform, as well as thelocking system. Each firmware independently handles: actuating
the motors for the horizontal movement or locking/unlocking thepins; pushing and pulling the pins, position tracking via magnetic
encoding, turning on/off the pulling electromagnet; checking forpins or device homing.

4.5

Technical evaluation and prototype
limitations

Seungwoo Je, et al.

We found an average of 3.9 pins (SD: 2.64) that incorrectly rendered, leading to an accuracy of 99.7% (SD=0.22). These rare failures were caused by the pin dropping down before the locking
system was able to activate. We measured 2.9 seconds for the shapegenerator to push a row (when max height), and 1.1 seconds tomove to the next row, resulting in a total of 4 minutes for rendering
the full height terrain. Furthermore, a single pin without the locking
system can endure up to a mean force of 6.98 N (N = 100, SD = 1.43),
relying on temporal locks with magnets (forces measured with adigital force gauge, SHIMPO FGJN-5).
From these results, we shined some light also on our device’s
key limitations. Its main implementation is that it leverages a single
shape-generator to render the complete haptic floor, by moving
across the platform, row by row. While this design is cost-effective,by requiring a relatively small number of actuators for controllinga large amount of pins (a ratio 1:60), it is also inherently slow, as
only pins placed on the same row can be controlled at the sametime.
Nevertheless, these limitations can be circumvented with theappropriate interaction techniques at the application level. For example, it is not necessary to dynamically reconstruct a terrain witha high refresh rate: instead, the application designer can choose toactuate only small portions of the platform to render the interactive
elements that change more often. Our stepping-stones application,
described before, uses this mechanism: each rock thrown from thecliff only requires on average 30 s for rendering. Furthermore, theapplication designer can leverage on the tracking system and Elevate’s large surface area to selectively update only the parts of theplatforms where the user is not standing; in fact previous haptic
floors, such as TilePop, also use these techniques to keep the user
engaged while the device is updating [40]. In the next sections we
describe a set of applications aimed to explore these techniques, anda user study for measuring the impact of these system’s limitations
over the user’s sense of realism and enjoyment.

5

APPLICATIONS

To further showcase a wide range of uses of our device, we implemented four distinct applications: three virtual reality applications,and one stand-alone application that makes use of dynamic terrains.

5.1
Figure 9: Consecutively ascending pins to measure the error
rate of entire pins
We performed a series of tests aimed at measuring the accuracy
and the time required for rendering a synthetically generated terrain
on our Elevate haptic floor. As shown in 9, we constructed terrains
resembling stairs from level 0 to level 10 (15 cm); these were chosen
as they allow for quick manual inspection and enumeration of
mistakes. Specifically, the stairs were constructed so that each row
contained pins placed one level higher than the previous, and, once
reached level 10, they fold back to level 0. Starting points were
set randomly, so that none of the terrains tested were equal. We
recorded the number of incorrect pin placements and the total
rendering time by conducting 10 full cycles.

LandscapeWe developed a landscape application where users can experience
immersive places with various terrains in VR. As depicted in Figures 1, 3, and 10, users can feel the ground level difference of hills
and texture of stones in VR with their feet. The user can have uninterrupted seamless experience on the terrain while Elevate ispartially generating terrains.

Figure 10: Various terrain spots on Landscape application
For this application, we reproduce the surface of a virtual environment in the Unity 3D game engine via scripts that check theElevate: A Walkable Pin-Array for Large Shape-Changing Terrains

height of all objects on a “Floor” layer. For each pin, we cast a ray
downwards on the environment, and the layer masking enables
the selective rendering of objects by the designer, for example rendering rocks and terrain, but not a snowball rolling through theenvironment. Designers have the option to let the environment bestatic or dynamic, and control the refresh rate of the floor, which isbounded by the speed at which the device can update a section.
As a user may damage the actuator if pins are raised while theystand over them, the script additionally allows the designer todynamically mask a certain distance (mapped to rows) around a
set of targets such as the user’s feet. This creates a “dead zone”,
which does not get updated from the previous frame, making theactuator avoid the user’s space and a potential damage. A VIVE
controller is attached to a corner of the Elevate pins to align thevirtual environment with the physical display. Two VIVE trackers
are used to track the user’s feet as they walk in virtual reality.

5.2

Stepping Stones

While the landscape application generates static and continuous
topology, the stepping stone application sets up an interactive experience with a dynamic terrain that re-configures over time. The user
can interact by grabbing and throwing off a cliff some grey coloredstones. The purpose of this is to build a bridge that would allow tocross the canyon — a gap of 1.2m on the platform. When a thrownstone hits the bottom of the canyon, it starts to slowly rise up fromthe collided point. While it is lifting up, the shape generator forms
the wooden pins according to the expected stone position in the VR
environment. When the shape generator finishes the terrain, then
the texture of the stone changes just like the other rocks within the
VR environment, informing the user that the stone is ready to step
on.

5.3

CHI ’21, May 8–13, 2021, Yokohama, Japan

Figure 12: Six possible examples of stairs: (a),(b) straightascending and descending; (c) valley shaped; (d) mountainshaped; (e) u-shaped; (f) amphitheatre shaped.

5.4

Golf

Beyond VR, this application demonstrates playing a mini-golf inthe real physical world, in which the floor provides a dynamic
terrain for a physical golf ball to roll on. The users can design
various terrain patterns for mini-golf using an authoring web-basedgraphical interface. With this, they can select individual pins anddirectly adjust their heights, or they can use pattern brushes withan adjustable radius to quickly render linear or curved hills, holes,
slopes, and rocky textures. Map designers can also modify the depth
and the rotation of each of these brushes. Finally, they can savea sequence of terrain patterns as an animation that the hardware
system will playback in a loop. As a result, shown in Figure 13,
users can create an obstacle that elevates dynamically to challenge
the player.

StairsFigure 13: The web application to design the mini-golf field(left), playing the dynamic mini-golf application (right).

6
Figure 11: Descending from the Stair application in VRwith VIVE trackers (left), the user’s perspective of view—theblocks represent user’s feet (right).
The stairs application allows users to build various kinds ofstairs in the VR environment, providing adjustable parameters(width, length, height, number of steps) and different types of stairs
configurations, e.g., ascending, descending, u-shaped, mountainshaped, and valley shaped configurations (Figure 12). Users canthen wholly experience climbing a ramp of stairs, or sitting on its
steps. This gives to the users not only a visual but also the haptic
experience of height. Finally the users can dynamically design newstairs and adjust its parameters, so to physically experience inalmost real-time the results of new architectural configurations.

USER STUDY

We conducted a user study to investigate the perceived realism andenjoyment of walking over our device, as it rendered different typesof terrains for virtual reality.

6.1

Study design

Our study followed a within-subjects design with a single modality
factor: haptic (our device) vs. no-haptic experience (baseline
condition). In the haptic condition, the participants walked in a VR
simulation with terrains rendered using the Elevate system, whilein the no-haptic case, the users walked on the flat wooden platform(i.e., pins did not actuate).
Specifically, we utilized two of the applications described in theprevious section (stepping stone and landscape) and stitched them
together in a single coherent VR experience. We did so to allow
participants to be immersed in a single VR scene that allows themto experience both dynamic elements of the terrain (the stepping

CHI ’21, May 8–13, 2021, Yokohama, Japan

Seungwoo Je, et al.

stones), and large detailed features of the landscape. The application switching was scripted as part of the experience, with users
required to briefly look at the sky after having crossed the canyon— an expedient needed to render the incoming terrain. By design,
this change of scenery required users to remain still while looking
around, waiting for the terrain to be reshaped. This, purposely,
allowed us to investigate whether a forced pause during the application would disrupt the enjoyment of the VR experience.

.
Figure 14: A participant experiencing terrains during the experiment; on the left we depict a scene from our steppingstone VR application; while on the right a scene from ourlandscape VR application.

6.2

Participants

We recruited eight participants from our local institution (two females, and six males) aged 23-39 years old (M=28.5, SD=4.72) andof body weight between 60.1 - 79 Kg (M: 71.7, SD=6.70). Threeparticipants reported being familiar with both VR and haptic devices, while two others reported familiarity with one of the two.
Participants were compensated with 10 USD in local currency for
their time.

6.4

6.5

Results

Figure 15 shows the subjective assessment of realism and enjoyment
for both conditions. Results were analyzed using Friedman test followed by post-hoc pairwise analysis with Wilcoxon signed-rank
test (𝛼 = 0.05). We report statistically significant differences between the baseline and haptic conditions for both realism (𝑋 2 (2) =21.000, 𝑝 < 0.001) and enjoyment (𝑋 2 (2) = 18.280, 𝑝 < 0.001). The
post-hoc analysis further reveals that the haptic condition was rated
significantly better than the baseline regardless of the stage of theapplication, for both realism (landscape: 𝑍 = −2.527, 𝑝 = 0.012,
stepping stones: 𝑍 = −2.536, 𝑝 = 0.011) and enjoyment (landscape:𝑍 = −2.386, 𝑝 = 0.017, stepping stones: 𝑍 = −2.536, 𝑝 = 0.011);
respectively, these findings support our H1 and H2.

Hypotheses

Our main hypothesis was that experiencing the VR environment by
walking on top of our haptic floor would create a higher sense ofrealism than in the baseline condition (H1). Secondly, we postulated
that experiencing the VR environment by walking on our haptic
floor would be more enjoyable for participants than the baseline
condition (H2).

6.3

landscape). Before concluding the study, we also conducted a semistructured interview aiming to extract qualitative observations andcomments about their experience. The experiment took in total
about 40 minutes to complete.

Procedure

After completing a demographics intake form, participants wereasked to experience the applications (for at least 5 minutes) inboth conditions (haptic vs. visual-only) following previous research[13, 16, 17]. The order of conditions was fully counterbalanced.
For the whole duration of each condition, participants wore an
HTC Vive Cosmos Elite VR headset and their own shoes. Participants were instructed that they could terminate the experiment at
any time, and that, for safety measures, they had to turn aroundand wait outside of the actuated platform while the terrain was
regenerated.
An experimenter was present next to the participants all thetime for safety. After each condition, the participants were asked torate the perceived realism and enjoyment on a 7-point Likert scale(as in [13, 17]) for each part of the application (stepping stones andFigure 15: Participant’s perceived realism and enjoyment in
the application for baseline and elevate condition. We foundthat elevate improves both metrics. The error-bar represents
a 95% of confidence interval.

6.6

Qualitative findings

The qualitative findings that emerged from the interviews with ourparticipants further corroborate our previous results. All participants agreed that the VR experience using Elevate felt more realistic
and enjoyable, and, as a result, more immersive. For instance, P2
stated, "Experiencing the [stepping] stones was fascinating", whileothers described it as "amazing" (P5) and "fun" (P6). When asked
to comment on what they appreciated the most, P3 remarked that
"It was nice to experience the height and slope changes while I
walk[ed] on the landscape." Participants also commented about theresolution of the terrain’s details, reporting to be satisfied with it.
P3 described being able "to feel the geometry of the stone with myfoot", and P2 and P8 of being able to perceive terrains inclinations:"My ankles were tilted due to the slope [...] so I felt the height
and the slope very clearly" (P2). Some other participants, on thecontrary, expressed limitations regarding the resolution of details
in the landscape application, commenting that "the slope difference
was not that clear" (P4) and that the resolution of curved objects
was "a bit disappointing" (P6), but nonetheless was felt more realistic than in the visual-only condition. Additionally, participants
reported that they felt confident in walking across the device. Five

Elevate: A Walkable Pin-Array for Large Shape-Changing Terrainsparticipants reported that the device felt "solid" (P5, P7) and thatthey trusted the locking mechanisms (P4, P6, P8).
When asked which part of the VR application participants preferred, all participants agreed that the stepping stone was moreenjoyable than the landscape; this was unsurprising as it contained
more drastic physical elevations. P2, P5, and P6 responded that it
was more realistic and enjoyable because they could feel the "extreme reality of a cliff with their toes". P1 and P7 mainly appreciatedthe game dynamics of the application, such as throwing stones andstepping on them: "grabbing and throwing the stone, and watching
the stone lifting up slowly made me the entire experience pleasurable" (P3). Realism also played an important role, as participants
felt more scared about being on the edge of a cliff: "I was extremely
horrified when I moved closer to the cliff edge. I truly felt that I
was this close to fall." (P4) and "I was much scared because I could
feel the empty space with my feet."(P5).
Finally, when asked about what needs further improvements,
all participants except one responded that they would like theterrain generator to act faster. Indeed, they remarked that the pause
between the stitched applications felt "long" and "boring". P2, who
did not feel bored, commented that "I didn’t feel bored when the pins
were transitioning (...) I was watching and observing the other partsof the scene". This comment suggests opportunities for designing
entertaining expedients while participants are required to wait forparts of the terrain to reshape; similar to what previous slow haptic
displays, such as TilePoP [40] implemented to engage their users
while waiting for the device to refresh (5-20 seconds needed). Finally,
unsurprisingly, five participants (P2, P3, P4, P6, P8) requested thatthe terrain be made even larger, and with even higher resolution:"[the resolution] was enough for wearing shoes, but it is not enoughfor barefoot" (P3). The next section of this paper follows up this listof limitations and describes opportunities for future improvements.

7

DISCUSSION AND FUTURE WORK

Our user study has established the benefits of how the device adds
to immersive experience in VR environment. However, there arelimitations and possible avenues for improvements. First, the main
issue raised in the study was, as expected, the refresh rate of ourcurrent implementation. While quick terrain updates, such as theappearance of a stone in the VR canyon, did not disturb the senseof immersion, the same was not true for longer updates that reconfigured the entire area; here, our participants had to wait. To
solve this issue, one can either increase the number of actuators in
the device or add a secondary shape generator to halve the transformation time. Secondly, participants requested a wider terrain
area. This can be improved by extending the pin rows, which does
not increment the cost proportionately to the number of pins since
its sharing the same shape generator. Also, terrains can be "virtually" extended using space-folding and redirecting techniques asshown in previous work [19, 34]. Third, few participants raised theissue of limited pin height resolution, we agree that the higher resolution and the pin height would expand the rendering spectrum,
however, our pin height (3×3×15 cm, 10 steps with 1.5cm/step) is
chosen in consideration of the height of the device, the weight ofthe material, the user, and the resulting cost. Compared to previous
research, our pins are smaller but longer ([16]: 5×5×10 cm), and

CHI ’21, May 8–13, 2021, Yokohama, Japan

more importantly, each pin can support the full weight of a user.
Lastly, we explicitly did not set any restrictions on participants’shoes, hoping to show Elevate’s applicability to real-case scenarios.
However, different shoes may affect the haptics on the feet. Indeed,
our study, despite being agnostic of the shoes’ sole, demonstrates
that the perceived realism has increased for the Elevate condition
compared to VR on a flat surface.
For future work, we plan to investigate the perception on humannavigation on a pin-array terrain, and thresholds of a pin size andheights of the pin-array display. We also plan to develop applications based on haptic illusion like in [19, 20, 26, 34] to extend
the potential usage of the device and accomplish real-walking VR
experience [3, 4, 45, 49]. Regarding the technical work, we will
improve the hardware to achieve different means of interactions.
For example, by changing the size of the pins, we could render
furniture and provide whole-body interactions as in [35, 36, 40].
Also, mobilizing the pin-array terrain [10, 31] would allow to coverlarger VR environment without scaling the number of pins. Finally,
additional features such as sensing pressure, controlling stiffness,
and actuating vibro-tactile motors could be employed to enhancevarious interactions, similarly to [21, 22, 44, 48].

8

CONCLUSION

In this paper, we introduced Elevate a walkable high-resolution
pin-array display that can render a variety of physical terrains for
VR simulations. Elevate has four key characteristics that distinguishit from other previous works: 1) it withstands human weights; 2)
its feedback is dynamic; 3) it is a large walkable surface; 4) it has anunprecedented resolution of 1,200 pins. To show the design spaceof Elevate we then designed a set of VR and phsyical applications(landscape; stepping stone; stairs; and non-VR mini-golf) which
demonstrates how designers can take advantage of the system’s
unique capabilities and avoid some of the inherent limitations. Finally, though a user study with eight participants, we showed that
Elevate provides a richer degree of realism and immersion, resulting
in measurable increase of enjoyment of walkable VR experiences.

ACKNOWLEDGMENTS
This research was supported by the MSIT (Ministry of Science andICT), Korea, under the Grand Information Technology ResearchCenter support program (IITP-2021-2015-0-00742) supervised by
the IITP (Institute for Information & communications Technology
Planning & Evaluation).

REFERENCES[1] Laroussi Bouguila, Béat Hirsbrunner, Makoto Sato, and Masaru Iwashita. 2003.
Virtual Locomotion Interface with Ground Surface Simulation.. In ICAT.
[2] Nicolas Bouillot and Micha Seta. 2019. A Scalable Haptic Floor dedicated to large
Immersive SpaceWohlaufs. In Proceedings of the 17th Linux Audio Conference(LAC-19), CCRMA, Stanford University, USA (2019), Vol. 5.
[3] Elodie Bouzbib, Gilles Bailly, Sinan Haliyo, and Pascal Frey. 2020. CoVR: A LargeScale Force-Feedback Robotic Interface for Non-Deterministic Scenarios in VR.
In Proceedings of the 33rd Annual ACM Symposium on User Interface Software andTechnology (Virtual Event, USA) (UIST ’20). Association for Computing Machinery,
New York, NY, USA, 209–222. https://doi.org/10.1145/3379337.3415891[4] Lung-Pan Cheng, Thijs Roumen, Hannes Rantzsch, Sven Köhler, Patrick Schmidt,
Robert Kovacs, Johannes Jasper, Jonas Kemper, and Patrick Baudisch. 2015.
TurkDeck: Physical Virtual Reality Based on People. In Proceedings of the 28th
Annual ACM Symposium on User Interface Software &amp; Technology (Charlotte,

CHI ’21, May 8–13, 2021, Yokohama, JapanNC, USA) (UIST ’15). Association for Computing Machinery, New York, NY, USA,417–426. https://doi.org/10.1145/2807442.2807463[5] Imre Cikajlo, Jakob Oblak, and Zlatko Matjačić. 2011. Haptic floor for virtualbalance training. In 2011 IEEE world haptics conference. IEEE, 179–184. https://doi.org/10.1109/WHC.2011.5945482[6] Sean Follmer, Daniel Leithinger, Alex Olwal, Akimitsu Hogge, and Hiroshi Ishii.
2013. inFORM: Dynamic Physical Affordances and Constraints through Shapeand Object Actuation (UIST ’13). ACM Press, 417–426. https://doi.org/10.1145/
2501988.2502032[7] Erik Hill, Hiroyuki Hatano, Masahiro Fujii, and Yu Watanabe. 2014. Haptic
foot interface for language communication. In Proceedings of the 5th Augmented
Human International Conference. 1–4. https://doi.org/10.1145/2582051.2582060[8] John Hollerbach, David Grow, and Craig Parker. 2005. Developments in locomotion interfaces. In 9th International Conference on Rehabilitation Robotics, 2005.
ICORR 2005. IEEE, 522–525. https://doi.org/10.1109/ICORR.2005.1501156[9] Ryuta Ishikawa, Akifumi Inoue, and Tohru Hoshi. 2018. Investigating perceived
slope gradient in virtual environment with visuo-haptic interaction. In Proceedings of the 30th Australian Conference on Computer-Human Interaction. 559–562.
https://doi.org/10.1145/3292147.3292234[10] Hiroo Iwata, Hiroaki Yano, Hiroyuki Fukushima, and Haruo Noma. 2005. CirculaFloor [locomotion interface]. IEEE Computer Graphics and Applications 25, 1(2005), 64–67. https://doi.org/10.1109/MCG.2005.5[11] Hiroo Iwata, Hiroaki Yano, and Fumitaka Nakaizumi. 2001. Gait master: A
versatile locomotion interface for uneven virtual terrain. In Proceedings IEEE
Virtual Reality 2001. IEEE, 131–137. https://doi.org/10.1109/VR.2001.913779[12] Hiroo Iwata, Hiroaki Yano, Fumitaka Nakaizumi, and Ryo Kawamura. 2001.
Project FEELEX: Adding Haptic Surface to Graphics. In Proceedings of the 28th
Annual Conference on Computer Graphics and Interactive Techniques (SIGGRAPH’01). Association for Computing Machinery, New York, NY, USA, 469–476. https://doi.org/10.1145/383259.383314[13] Seungwoo Je, Myung Jin Kim, Woojin Lee, Byungjoo Lee, Xing-Dong Yang, Pedro
Lopes, and Andrea Bianchi. 2019. Aero-plane: A Handheld Force-Feedback Device
that Renders Weight Motion Illusion on a Virtual 2D Plane. In Proceedings of the
32nd Annual ACM Symposium on User Interface Software and Technology. 763–775.
https://doi.org/10.1145/3332165.3347926[14] Narae Lee, Ju-Whan Kim, Jungsoo Lee, Myeongsoo Shin, and Woohun Lee. 2012.
MoleBot: a robotic creature based on physical transformability. In Proceedings ofthe 2012 Virtual Reality International Conference. 1–4. https://doi.org/10.1145/
2331714.2331734[15] Daniel Leithinger, Sean Follmer, Alex Olwal, Samuel Luescher, Akimitsu Hogge,
Jinha Lee, and Hiroshi Ishii. 2013. Sublimate: State-Changing Virtual and PhysicalRendering to Augment Interaction with Shape Displays. In Proceedings of the
SIGCHI Conference on Human Factors in Computing Systems (CHI ’13). Association
for Computing Machinery, New York, NY, USA, 1441–1450. https://doi.org/10.
1145/2470654.2466191[16] Daniel Leithinger, David Lakatos, Anthony DeVincenzi, Matthew Blackshaw, andHiroshi Ishii. 2011. Direct and Gestural Interaction with Relief: A 2.5D Shape
Display. In Proceedings of the 24th Annual ACM Symposium on User Interface
Software and Technology (UIST ’11). Association for Computing Machinery, New
York, NY, USA, 541–548. https://doi.org/10.1145/2047196.2047268[17] Pedro Lopes, Sijing You, Lung-Pan Cheng, Sebastian Marwecki, and Patrick
Baudisch. 2017. Providing Haptics to Walls & Heavy Objects in Virtual Reality by
Means of Electrical Muscle Stimulation. In Proceedings of the 2017 CHI Conferenceon Human Factors in Computing Systems (Denver, Colorado, USA) (CHI ’17).
Association for Computing Machinery, New York, NY, USA, 1471–1482. https://doi.org/10.1145/3025453.3025600[18] Maud Marchal, Gabriel Cirio, Yon Visell, Federico Fontana, Stefania Serafin,
Jeremy Cooperstock, and Anatole Lécuyer. 2013. Multimodal rendering of walking over virtual grounds. In Human Walking in Virtual Environments. Springer,
263–295. https://doi.org/10.1007/978-1-4419-8432-6_12[19] Keigo Matsumoto, Yuki Ban, Takuji Narumi, Yohei Yanase, Tomohiro Tanikawa,and Michitaka Hirose. 2016. Unlimited Corridor: Redirected Walking Techniques
Using Visuo Haptic Interaction. In ACM SIGGRAPH 2016 Emerging Technologies(Anaheim, California) (SIGGRAPH ’16). Association for Computing Machinery,
New York, NY, USA, Article 20, 2 pages. https://doi.org/10.1145/2929464.2929482[20] Ryohei Nagao, Keigo Matsumoto, Takuji Narumi, Tomohiro Tanikawa, and Michitaka Hirose. 2017. Infinite stairs: simulating stairs in virtual reality based on
visuo-haptic interaction. In ACM SIGGRAPH 2017 Emerging Technologies. 1–2.
https://doi.org/10.1145/3084822.3084838[21] Ken Nakagaki, Daniel Fitzgerald, Zhiyao Ma, Luke Vink, Daniel Levine, andHiroshi Ishii. 2019. inFORCE: Bi-directionalForce’Shape Display for Haptic
Interaction. In Proceedings of the Thirteenth International Conference on Tangible,
Embedded, and Embodied Interaction. 615–623. https://doi.org/10.1145/3294109.
3295621[22] Ken Nakagaki, Yingda Liu, Chloe Nelson-Arzuaga, and Hiroshi Ishii. 2020.
TRANS-DOCK: Expanding the Interactivity of Pin-based Shape Displays by
Docking Mechanical Transducers. In Proceedings of the Fourteenth International Conference on Tangible, Embedded, and Embodied Interaction. 131–142.

Seungwoo Je, et al.

https://doi.org/10.1145/3374920.3374933[23] Niels Christian Nilsson, Stefania Serafin, Frank Steinicke, and Rolf Nordahl. 2018.
Natural walking in virtual reality: A review. Computers in Entertainment (CIE)
16, 2 (2018), 1–22. https://doi.org/10.1145/3180658[24] H. Noma, T. Sugihara, and T. Miyasato. 2000. Development of Ground Surface
Simulator for Tel-E-Merge System. In Proceedings IEEE Virtual Reality 2000 (Cat.
No.00CB37048). 217–224. https://doi.org/10.1109/VR.2000.840501[25] Ivan Poupyrev, Tatsushi Nashida, and Makoto Okabe. 2007. Actuation andTangible User Interfaces: The Vaucanson Duck, Robots, and Shape Displays.
In Proceedings of the 1st International Conference on Tangible and Embedded
Interaction (TEI ’07). Association for Computing Machinery, New York, NY, USA,
205–212. https://doi.org/10.1145/1226969.1227012[26] Sharif Razzaque. 2005. Redirected Walking. Ph.D. Dissertation. USA. Advisor(s)Brooks, Fredrick P.
[27] AF Rovers and HA Van Essen. 2006. Guidelines for haptic interpersonal communication applications: an exploration of foot interaction styles. Virtual Reality 9,
2-3 (2006), 177–191. https://doi.org/10.1007/s10055-005-0016-0[28] Dominik Schmidt, Rob Kovacs, Vikram Mehta, Udayan Umapathi, Sven Köhler,
Lung-Pan Cheng, and Patrick Baudisch. 2015. Level-ups: Motorized stilts thatsimulate stair steps in virtual reality. In Proceedings of the 33rd Annual ACM
Conference on Human Factors in Computing Systems. 2157–2160. https://doi.org/
10.1145/2702123.2702253[29] Dominik Schmidt, Raf Ramakers, Esben W Pedersen, Johannes Jasper, Sven
Köhler, Aileen Pohl, Hannes Rantzsch, Andreas Rau, Patrick Schmidt, ChristophSterz, et al. 2014. Kickables: tangibles for feet. In Proceedings of the SIGCHI
Conference on Human Factors in Computing Systems. 3143–3152. https://doi.org/
10.1145/2556288.2557016[30] Henning Schmidt, Stefan Hesse, Rolf Bernhardt, and Jörg Krüger. 2005.
HapticWalker—a novel haptic foot device. ACM Transactions on Applied Perception(TAP) 2, 2 (2005), 166–180. https://doi.org/10.1145/1060581.1060589[31] Alexa F. Siu, Eric J. Gonzalez, Shenli Yuan, Jason B. Ginsberg, and Sean Follmer.
2018. ShapeShift: 2D Spatial Manipulation and Self-Actuation of Tabletop Shape
Displays for Tangible and Haptic Interaction. In Proceedings of the 2018 CHI
Conference on Human Factors in Computing Systems (Montreal QC, Canada)(CHI ’18). Association for Computing Machinery, New York, NY, USA, 1–13.
https://doi.org/10.1145/3173574.3173865[32] Hyungki Son, Hyunjae Gil, Sangkyu Byeon, Sang-Youn Kim, and Jin Ryong Kim.
2018. Realwalk: Feeling ground surfaces while walking in virtual reality. In
Extended Abstracts of the 2018 CHI Conference on Human Factors in Computing
Systems. 1–4. https://doi.org/10.1145/3170427.3186474[33] Toshiaki Sugihara and Tsutomu Miyasato. 1998. The terrain surface simulator
ALF (Alive! Floor). Proc. of VRSJ ICAT’98 (1998), 170–174.
[34] E. A. Suma, Z. Lipps, S. Finkelstein, D. M. Krum, and M. Bolas. 2012. Impossible Spaces: Maximizing Natural Walking in Virtual Environments with SelfOverlapping Architecture. IEEE Transactions on Visualization and Computer
Graphics 18, 4 (2012), 555–564. https://doi.org/10.1109/TVCG.2012.47[35] Ryo Suzuki, Hooman Hedayati, Clement Zheng, James L Bohn, Daniel Szafir, Ellen
Yi-Luen Do, Mark D Gross, and Daniel Leithinger. 2020. RoomShift: Room-scale
Dynamic Haptics for VR with Furniture-moving Swarm Robots. In Proceedingsof the 2020 CHI Conference on Human Factors in Computing Systems. 1–11. https://doi.org/10.1145/3313831.3376523[36] Ryo Suzuki, Ryosuke Nakayama, Dan Liu, Yasuaki Kakehi, Mark D. Gross,and Daniel Leithinger. 2020. LiftTiles: Constructive Building Blocks for Prototyping Room-Scale Shape-Changing Interfaces. In Proceedings of the Fourteenth International Conference on Tangible, Embedded, and Embodied Interaction(TEI ’20). Association for Computing Machinery, New York, NY, USA, 143–151.
https://doi.org/10.1145/3374920.3374941[37] Ryo Suzuki, Junichi Yamaoka, Daniel Leithinger, Tom Yeh, Mark D. Gross, Yoshihiro Kawahara, and Yasuaki Kakehi. 2018. Dynablock: Dynamic 3D Printing for
Instant and Reconstructable Shape Formation. In Proceedings of the 31st Annual
ACM Symposium on User Interface Software and Technology (Berlin, Germany)(UIST ’18). Association for Computing Machinery, New York, NY, USA, 99–111.
https://doi.org/10.1145/3242587.3242659[38] Yuichiro Takeuchi. 2010. Gilded gait: reshaping the urban experience withaugmented footsteps. In Proceedings of the 23nd annual ACM symposium on Userinterface software and technology. 185–188. https://doi.org/10.1145/1866029.
1866061[39] Andrew S. Tanenbaum and Herbert Bos. 2014. Modern Operating Systems (4thed.). Prentice Hall Press, USA.
[40] Shan-Yuan Teng, Cheng-Lung Lin, Chi-huan Chiang, Tzu-Sheng Kuo, Liwei
Chan, Da-Yuan Huang, and Bing-Yu Chen. 2019. TilePoP: Tile-Type Pop-up
Prop for Virtual Reality. In Proceedings of the 32nd Annual ACM Symposium on
User Interface Software and Technology (UIST ’19). Association for Computing
Machinery, New Orleans, LA, USA, 639–649. https://doi.org/10.1145/3332165.
3347958[41] Luca Turchet, Paolo Burelli, and Stefania Serafin. 2012. Haptic feedback forenhancing realism of walking simulations. IEEE transactions on haptics 6, 1 (2012),
35–45. https://doi.org/10.1109/TOH.2012.51

Elevate: A Walkable Pin-Array for Large Shape-Changing Terrains[42] Yon Visell and Jeremy R Cooperstock. 2010. Design of a vibrotactile display via arigid surface. In 2010 IEEE haptics symposium. IEEE, 133–140. https://doi.org/10.
1109/HAPTIC.2010.5444664[43] Yon Visell, Jeremy R Cooperstock, Bruno L Giordano, Karmen Franinovic, Alvin
Law, Stephen McAdams, Kunal Jathal, and Federico Fontana. 2008. A vibrotactile device for display of virtual ground materials in walking. In International
Conference on Human Haptic Sensing and Touch Enabled Computer Applications.
Springer, 420–426. https://doi.org/10.1007/978-3-540-69057-3_55[44] Yon Visell, Alvin Law, and Jeremy R Cooperstock. 2009. Touch is everywhere:
Floor surfaces as ambient haptic interfaces. IEEE Transactions on Haptics 2, 3
(2009), 148–159. https://doi.org/10.1109/TOH.2009.31[45] Yuntao Wang, Zichao (Tyson) Chen, Hanchuan Li, Zhengyi Cao, Huiyi Luo,
Tengxiang Zhang, Ke Ou, John Raiti, Chun Yu, Shwetak Patel, and Yuanchun
Shi. 2020. MoveVR: Enabling Multiform Force Feedback in Virtual Reality Using
Household Cleaning Robot. In Proceedings of the 2020 CHI Conference on Human
Factors in Computing Systems (Honolulu, HI, USA) (CHI ’20). Association for
Computing Machinery, New York, NY, USA, 1–12. https://doi.org/10.1145/
3313831.3376286[46] Yue Wang and Mark A Minor. 2014. Design of a bladder based elastomeric
Smart Shoe for haptic terrain display. In 2014 IEEE/RSJ International Conferenceon Intelligent Robots and Systems. IEEE, 1236–1241. https://doi.org/10.1109/IROS.
2014.6942715

CHI ’21, May 8–13, 2021, Yokohama, Japan[47] Anne Wohlauf, Fabian Hemmert, and Reto Wettach. 2017. The Haptic Body
Scale: Designing Imprecision in Times of the Quantified Self. In Proceedingsof the Eleventh International Conference on Tangible, Embedded, and Embodied
Interaction (Yokohama, Japan) (TEI ’17). Association for Computing Machinery,
New York, NY, USA, 367–373. https://doi.org/10.1145/3024969.3025003[48] Xiao Xiao, Donald Derek Haddad, Thomas Sanchez, Akito van Troyer, Rébecca
Kleinberger, Penny Webb, Joe Paradiso, Tod Machover, and Hiroshi Ishii. 2016.
Kinéphone: Exploring the Musical Potential of an Actuated Pin-Based Shape
Display.. In NIME. 259–264.
[49] Yan Yixian, Kazuki Takashima, Anthony Tang, Takayuki Tanno, Kazuyuki Fujita,
and Yoshifumi Kitamura. 2020. ZoomWalls: Dynamic Walls That Simulate Haptic
Infrastructure for Room-Scale VR World. In Proceedings of the 33rd Annual ACM
Symposium on User Interface Software and Technology (Virtual Event, USA) (UIST’20). Association for Computing Machinery, New York, NY, USA, 223–235. https://doi.org/10.1145/3379337.3415859[50] Shigeo Yoshida, Yuqian Sun, and Hideaki Kuzuoka. 2020. PoCoPo: Handheld
Pin-Based Shape Display for Haptic Rendering in Virtual Reality. In Proceedingsof the 2020 CHI Conference on Human Factors in Computing Systems (Honolulu,
HI, USA) (CHI ’20). Association for Computing Machinery, New York, NY, USA,
1–13. https://doi.org/10.1145/3313831.3376358[51] K. Zhang and S. Follmer. 2018. Electrostatic adhesive brakes for high spatial
resolution refreshable 2.5D tactile shape displays. In 2018 IEEE Haptics Symposium(HAPTICS). 319–326. https://doi.org/10.1109/HAPTICS.2018.8357195