Coordination Policies for Co-located Collaborative Travel

Andreas Simon∗ Christian Stern†

FHNW Academy of Art and Design

ABSTRACT

To make virtual environment experiences more engaging, we propose to use multiple interaction devices and to support collabo-rative travel for co-located groups of users. Results of a prelimi-nary pilot study of a collaborative travel task for pairs of users in a projection-based display system suggest that the use of multiple controllers is much more effective and satisfying than swapping and sharing a single device. The study also highlights functional differences between coordination policies for collaborative travel. KEYWORDS: Co-located collaboration, coordination, travel. INDEX TERMS: I.3.6 [Computer Graphics]: Methodology and Techniques - Interaction techniques; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism - Virtual reality

1 INTRODUCTION

For interaction, practically all installations of projection-based display systems today support only one interaction device that is typically used by a single “master user” or guide. We think there are many good reasons to give all users in a virtual environment an interaction device. Game consoles often have multiple con-trollers for a small group of players. Inkpen et al. [3], in a study of control passing protocols for collaboration in children, report that, “One interesting characteristic of children playing single-player video games is that occasionally one of the children will sit hold-ing the inactive controller while waiting for a turn. Why is it important to hold on to a device that has no impact on the game? Perhaps there is a heightened sense of control?”

In this work we propose to give every co-located user in a pro-jection-based display system a device for motion control and to use suitable coordination policies to better support collaborative travel. Results from a preliminary study of collaborative travel for two users suggest that the use of multiple controllers is more effective and satisfying than physically swapping and sharing a single device between users. Also, the study highlights functional differences between coordination policies.

2 BACKGROUND

The benefits of using virtual environments for collaboration and for providing a shared experience have been recognized for a long time. the ability to simply share the view with multiple people has been one of the major practical successes of large projection-based display systems [1].

While there is a substantial body of research on distributed col-laborative navigation and the coordination of individual view-points [2][6], there is practically no work on navigation techniques for groups of co-located users with a single, common

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Figure 1. Collaborative navigation with two interaction devices

viewpoint. We find this type of collaborative travel in interactive theatre presentations and theme park rides. In the interactive Kyongju VR Theatre presentation [5], a voting scheme allows each member of a large audience to use his keypad to collectively control the motion of a flock of butterflies. In Disney’s Virtual Jungle Cruise [4], four guests sit in a rubber raft and use paddles to row and steer a virtual river raft together. In this case, partici-pants are engaged by trying to figure out how to coordinate their rowing motions to control the raft.

Our contribution is to introduce the use of multiple interaction devices for co-located collaborative travel in projection-based display systems and to explore suitable coordination policies for collaborative motion control of a common viewpoint.

3 COORDINATION POLICIES

We have implemented and explored a number of different coordi-nation policies, suitable for collaborative motion control. Using only a single device is a very simple and natural way to coordinate co-located collaboration. Users first have to compete for control of the physical device, but once they have possession of the device it is clear who controls the application. While connecting multiple interaction devices to an application is relatively straight-forward, combining multiple inputs and mitigating collisions and interferences between users presents a more challenging problem.

Implicit coordination policies interpret the action of a user to determine his intention to take or to release control. When a user pushes the motion controller (with a small threshold to remove spurious touches), he implicitly wishes to take control, when he releases the controller (possibly after a short timeout), he implic-itly offers to release control. Combine implements a no-control policy. It combines the motion input of all active users by adding the vectors for motion speed and factoring the spin for rotation. This behavior is similar to voting schemes used for control by large audiences [5]. While it seems that groups develop a combined coordination skill, the input of other users is not transparent and impossible to anticipate.

∗email: ansimon@gmail.com †email: stern@ifi.unizh.ch

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Give implements a first-takes-all scheme. While a user is in con-trol and moving, other users are blocked out and cannot take con-trol. The user currently in control maintains control until he stops. Releasing the controller implicitly releases control. All users can now race to take control by pushing their controller, the first re-quest is granted control. Brake implements a compromise between the permissive com-bine and the restrictive give schemes. The user currently in con-trol maintains control until he stops. Other users trying to get control by pushing their controller will slow down the controlling user, but can not influence motion direction or get control. Stop-ping releases control, and now all users can take control by push-ing their controller to move. The first request is granted control. Take enables users to interrupt a controlling user at any time. By pushing the controller to move, a user immediately takes control. A user who has lost control has to first release the controller before he can push the controller to again take control and move.

Explicit coordination policies establish an additional, separate interface to negotiate control. Only after managing control, e.g. by pressing a button to explicitly request or release control, users can use the motion controller to travel. Explicit Give is similar to the give scheme implemented by Ink-pen et al. [3]. A user maintains control and can travel until he explicitly gives up control by pressing a button. After control is explicitly released, all users can implicitly take control by pushing the controller. The first request is granted control. Explicit Take is similar to the implementation of take by Inkpen et al. Anyone can interrupt and explicitly take control at any time, even while another user is in control, by pressing a button. A user maintains control until another user explicitly takes control.

Coordination policies differ not only by the way they arbitrate access to a limited resource between multiple users. An important aspect that may substantially influence performance is the way different coordination schemes provide feedback on the state of arbitration. For motion control it is practically impossible to see that a user is manipulating the motion controller and the interac-tion is largely invisible. Currently, we provide additional visual feedback on collisions, when a user requests control but is re-jected. This feedback is useful for the controlling user as it allows him to decide, if appropriate, to quickly release control so that the other user can take over.

4 PILOT STUDY

Usability of different coordination policies for a pair of users in a simple travel task was evaluated in a preliminary pilot study with four groups of two subjects. Our experimental setup uses a 2.1m x 3m L-shaped floor-and-wall stereoscopic projection system with two Ascension Wanda devices for motion control (Figure 1). The task consists of subjects hitting stationary targets by driving through them. Each subject is assigned a color (red/green) and only hitting targets of the respective color increases the score, forcing users to swap and share control between them. After the test we conducted a short interview and subjects were asked to rank control policies by preference.

Swapping the single device between users did not perform well, delivering only about 60% of the performance for multiple de-vices, regardless of coordination policy. It was also ranked the least favorite technique by all subjects.

Of the coordination policies, the give policy showed the best performance, allowing users to concentrate on the task without being interrupted. The brake control policy exhibited the easiest and most frequent change of control between users and showed the most even distribution of control time. Also, it was ranked as the favorite coordination policy by most subjects. We believe that the brake scheme can give good implicit feedback on contention, without disturbing motion control for the user in control.

Users generally preferred implicit over explicit coordination policies. The explicit give technique seemed to perform least well of all tested coordination policies. It resulted in the lowest task performance and exhibited problems with balanced exchange of control. Explicitly releasing control was frequently forgotten, producing more verbal communication than with the other tech-niques. It was also ranked least favorite of the coordination poli-cies (but still ranked better than swapping a single device).

5 CONCLUSION AND FUTURE WORK

We have presented the use of multiple interaction devices to sup-port collaborative travel for a co-located group of users. To allow shared access to move the common viewpoint, we have intro-duced a set of coordination policies, suitable for collaborative travel. A preliminary pilot study indicates that collaborative travel with multiple, individual devices can indeed perform much better than the customary swapping of a single device between users. Performance of the single device, swapped between users to share control in the task, is substantially lower than performance for the use of multiple devices.

By bringing together aspects from virtual environment research on travel and navigation and from single display group-ware, we believe there are numerous research opportunities connected with the concept of co-located collaborative travel. Future work will corroborate the preliminary study results with further research, in particular on the role of feedback for the quality of coordination.

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