8/10/2019 Bend desk

1/10

ITS 2010: Displays November 7-10, 2010, Saarbrucken, Germany

1

BendDesk: Dragging Across the Curve

Malte Weiss Simon Voelker Christine Sutter Jan Borchers

RWTH Aachen University

52056 Aachen, Germany{weiss, voelker, borchers}@cs.rwth-aachen.dechristine.sutter@psych.rwth-aachen.de

ABSTRACT

We present BendDesk, a hybrid interactive desk system thatcombines a horizontal and a vertical interactive surface viaa curve. The system provides seamless touch input acrossits entire area. We explain scalable algorithms that providegraphical output and multi-touch input on a curved surface.In three tasks we investigate the performance of dragginggestures across the curve, as well as the virtual aiming attargets. Our main findings are: 1) Dragging across a curve issignificantly slower than on flat surfaces. 2) The smaller theentrance angle when dragging across the curve, the longerthe average trajectory and the higher the variance of trajecto-ries across users. 3) The curved shape of the system impairsvirtual aiming at targets.

ACM Classification: H5.2 [Information interfaces and pre-sentation]: User Interfaces. - Input Devices and Strategies.

General terms: Design, Human Factors

Keywords: Curved surface, desk environment, multi-touch,dragging, virtual aiming.

INTRODUCTION

A typical computer workplace integrates horizontal and ver-tical surfaces into a workspace. It encompasses at least one ormore vertical displays that show digital content and a largerhorizontal area, containing input devices, such as mouseand keyboard, paper-based documents, and everyday objects.Touch recognition technologies have combined the benefitsof traditional input metaphors with digital documents [24].Tablets allow high precision stylus input for graphic design;digital pens, such as Anoto1, enable annotations on physicalpaper; and multi-touch gestures [4] provide an intuitive wayto transform and modify digital data. However, despite allthe advantages these interfaces have barely found their way

into everyday workspaces yet.

1www.anoto.com

Permission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies arenot made or distributed for profit or commercial advantage and that copiesbear this notice and the full citation on the first page. To copy otherwise, torepublish, to post on servers or to redistribute to lists, requires prior specificpermission and/or a fee.

ITS10,November 710, 2010, Saarbrucken, Germany.

Copyright 2010 ACM 9781450303996/10/11...$10.00.

Figure 1: BendDesk seamlessly merges a horizontaland a vertical interactive surface with a curve.

Many systems have been proposed that use vertical and hor-

izontal interactive surfaces within a single desk environment(e.g., [7, 16]). They provide a large interactive area and allowto move digital objects across multiple displays. However,those systems suffer from a lack of spatial continuity. Ac-cording to the Gestalt Law of Closure [5], gaps between ad-

jacent displays suggest isolated interactive areas. Other lawsmay be violated that are useful in screen design, e.g., the Lawof Proximity, because objects belonging together may be sep-arated across the gap. Furthermore, splitting objects acrossbezels impairs search accuracy and tunnel steering perfor-mance [2]. Finally, those setups limit the applicability of di-rect manipulation, as movement trajectories are interruptedwhen dragging a finger or pen from screen to screen.

In this paper, we present BendDesk, a desk environment thatmerges a vertical and a horizontal multi-touch surface intoone interactive surface using a curve (Figure 1). Our systemprovides a large interactive area within the users reach andallows uninterrupted, seamless dragging gestures across theentire surface. The focus of this paper is to explore the ef-fects of a curve between two orthogonal surfaces on one ofthe most basic gestures: dragging. Our results can informthe design of more complex gestures, as most of these canbe subdivided into elementary dragging and pointing opera-tions.

8/10/2019 Bend desk

2/10

ITS 2010: Displays November 7-10, 2010, Saarbrucken, Germany

2

(a) Placing of projectors and cameras.

board

curve

tabletop

(b) Interactive areas of the BendDesk system. (c) Manual screen calibration.

Figure 2: Hardware setup and screen calibration.

RELATEDWORK

Our project was inspired by the Sun Starfire video pro-totype from 1994 that intended to predict a potential futureworkplace in 2004 [23]. The envisioned system featured alarge, interactive area, different input modalities such as ges-tures and direct manipulation, and applications, such as re-

mote collaboration.

In recent years, the specific characteristics of horizontal andvertical interactive surfaces have received great interest inthe research community. According to Morris et al. [18],horizontal surfaces are more appropriate for annotation andpen-based note-taking, while vertical displays support read-ing and intensive writing tasks using keyboards. Since nodisplay seems appropriate for all potential tasks, Morris etal. propose a hybrid system. In a later paper [17], they re-port on a field study involving multiple horizontal and ver-tical screens. Although participants were enthusiastic aboutthe extra space, one problem reported was that the horizontaland vertical screens were perceived as isolated areas. Some

studies [17, 19] indicate that interactive surfaces should al-low tilting to increase comfort, such as the FLUX table [15].However, Morris et al. also emphasize that desk environ-ments should fit into the ecologies of objects. For example, atable should allow users to put down everyday objects. Thiscoincides with observations in a long-term study by Wigdoret al. [26]. The authors point out the dual use of interactivetabletops as computing devices and as pieces of furniture. Intheir study, the participant tended to tilt the table at an anglethat avoided objects to fall from the table.

The combination of horizontal and vertical interactive sur-faces has mostly been applied to two applications: collab-orative workspaces and remote desks. While tabletops aresuitable for face-to-face group work and provide awarenessof each others actions, interactive boards can provide anoverview of information shared among groups. Accordingly,many systems have been developed that integrate vertical andhorizontal interactive surfaces into collaborative workspacesin order to add digital capabilities [8, 13, 21, 25]. The incor-poration of both surface types has also been applied to remotedesk environments. For example, the Agora system [16] andDigiTable [7] provide an interactive horizontal surface for aprivate document space and a vertical surface displaying a re-mote person via a video conferencing system. However, thevertical surface is non-interactive in most of these systems.

Nearly all multi-touch systems are limited to one or more flatinteractive devices. One exception is Sphere [1], a sphericalmulti-touch enabled display. Furthermore, the field of or-ganic interfaces [6, 11] proposes interactive non-planar sur-faces that can be freely deformed. Early examples of thisvision are Paper Windows [12] and Gummi [22]. Recently,

Curve [28] presented ergonomics and design considerationsfor building a curved multi-touch table.

DESIGN CONSIDERATIONS

We envisioned BendDesk as a multi-touch desk environmentthat supports interaction with digital documents but also re-spects the nature of traditional desks. Although there is ev-idence that tilted surfaces yield high acceptance for specifictasks (see above), we intentionally avoided them for two rea-sons: Firstly, we consider the support of the ecology of (ev-eryday) objects as crucial. With the exception of special pur-pose desks, such as drawing tables, office desks are usuallyhorizontal because people put physical objects on them. Incontrast, the possibilities of placing objects onto a tilted sur-

face, even at small angles, are limited. Secondly, tilting thevertical surface backwards would reduce its reachability atthe top.

We also accounted for ergonomic requirements: the usershould be able to sit in a comfortable position and to reachthe entire input area without much effort. We applied ISOnorm 9241-5 to choose the height of the table. Furthermore,we conducted preliminary user tests on an adjustable tableprototype to find the depth for the vertical surface. In thesetests, users perform pointing and dragging tasks where thedepth of the vertical surface was varied.

HARDWARE SETUP

As illustrated in Figure 2, our interactive desk consists of one104 cm 104 cm acrylic surface that is bent to yield twoorthogonal surfaces, seamlessly merged by a curve. The sur-face is mounted at 72 cm height2, on a half-closed woodenbox that contains all electronics, such as projectors for graph-ical output and cameras for touch input. The form factor ofour setup separates the device into three interactive areas: thevertical board(100 cm 43 cm), the curve (100 cm 16cm) with a radius of 10 cm, and the horizontal tabletop(100cm 40 cm). We choose a radius of 10 cm to provide a large

2following ISO 9241-5

8/10/2019 Bend desk

3/10

8/10/2019 Bend desk

4/10

8/10/2019 Bend desk

5/10

ITS 2010: Displays November 7-10, 2010, Saarbrucken, Germany

5

(1)horizontal

(2)curve

x-position(1) (2) (3) (4) (5) (6) (7)

(3)vertical

upwards downwards

area

Figure 4: Experimental design of vertical dragging

task.

cm), the interactive area went blank and the next trial wasdisplayed. They appeared in three different areas (in the hor-izontal plane, the curve, or the vertical plane), and draggingdirection from source to target was either upwards or down-wards. This resulted in 3 (area) 2 (dragging direction) ex-perimental conditions. We further controlled the distributionof trials across the surface by presenting trials on seven dif-ferent x-positions with two repetitions each. The order of tri-als was randomized. Participants worked throughout 84 tri-als with their dominant hand and throughout another 84 trialswith their non-dominant hand. This yielded a total number of168 dragging operations per participant. Dragging durationwas defined as the interval from touching the source untilcorrectly releasing it when the source was placed in the tar-get (given in ms). Dragging trajectory covered the observedlength of the fingers movement path, again from touchingthe source until correctly releasing it when the source wasplaced in the target (given in px).

We hypothesized the following outcomes:

H1(horizontal vs. vertical): Dragging (a) duration and (b)trajectory are shorter on the horizontal surface than on thevertical one.

H2 (planar vs. curve): Dragging (a) duration and (b) tra-jectory are shorter on planar surfaces than on the curved

area. H3(down vs. up): Dragging (a) duration and (b) trajectory

are shorter when moving upwards in GUI coordinates thanwhen moving downwards.

Results The data were analyzed for each of the dependentvariables with 3 2 analyses of variances (ANOVAs) withthe within-subject factorsareaanddirection. Dragging dura-tions are depicted in Figure 5. The ANOVA revealed a signif-icant main effect of the factor area(F(2, 34) = 14.20;p