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Appendix A - GreenSpace Prototype User's Guide

A.1 Introduction

This prototype of the GreenSpace virtual teleconferencing system was constructed in order to explore various aspects of my thesis, entitled Spatial Culling of Interpersonal Communication within Large-scale Multi-userVirtual Environments.

According to this thesis, users and networks of traditional multi-user virtual environment applications quickly become overloaded by positional, audio, and other types of interpersonal communication data from other users. This thesis explores intuitive and efficient techniques to reduce the cognitive and network loads with spatial culling.

This prototype allows many users to connect, via the Mbone, to a serverless (peer to peer communication only) virtual environment representing an architectural or teleconferencing application. Within this environment the users are able to see each other move around and can "listen" to what the other users have to say (audio is simulated by textual messages). For comparison, this prototype can be run in broadcast or multicast modes. While in multicast mode, the spatial culling technique is employed.

A.2 Obtaining a Userid

Before using the prototype you should request a unique id by mailing pulkka@cs.washington.edu and asking for a gsuser userid. As soon as I can, I will mail you a unique userid that is necessary for operating the prototype and will be used to identify any feedback you submit.

A.3 Starting the System

This prototype will run on any SGI in the HITLab or in CSE (both the Grail and gws machines, but not the iws machines). The program will not function, even remotely, on any other machines, as it requires your display to be GL capable.

Once you are sitting at an appropriate machine and have your userid, you should start both modes, broadcast and multicast, simutaneously from two different terminal windows.

(Figure)

Figure A.1: Example Desktop Setup for Prototype


Starting Broadcast mode:
This mode is started by executing the following at the command line:

In this environment you are tuned to a single multicast channel for sends and receives, as is everyone else in the environment. You receive position updates and "audio" broadcast from all users in the environment, regardless of their virtual position relative to you. This is considered the base case, as it was the typical approach to provide communication between users in some older virtual environ ments systems, including SIMNET. Unfortunately, this model does not scale well. As the number of users increase, the networks and users become overloaded with information.


Starting Multicast Mode (w/Spatial Culling):
This mode is started by executing the following at the command line:

This environment is automatically spatially partitioned into a grid of 10 by 10 multi cast groups. There is also a 101st multicast group that is used to broadcast group change announcements. As you move through the environment you send your position and communication data to the group that you are currently in, while lis tening to data being sent to that group and its 8 nearest neighbors. These 9 multi cast groups form your communication area. When users are outside of your communication area, you can see their approximate position based on their group change announcements (indicated by showing the user in the center of that com munication group). This is similar to the approach detailed in a NPS paper entitled Exploiting Reality with Multicast Groups, which was presented at VRAIS `95.

Furthermore, even when a user is in your communication area (which is rather large), you may not receive their "audio" data. The "audio" data is only displayed to you if you are within a specific virtual distance of the user sending the data (in this case, the width of a communication group is also the the radius of your hearing). Even within this radius, audio dropoff is simulated by informing you that "UserX is saying something, but is too far away to hear", if they are not within half the width of a communication area.

Unlike the broadcast model, this model does scale well, both in terms of the network load and the user's cogntive load.

A.4 User Interface

After a few moments of establishing the proper network connections, a GreenSpace User window will appear (the world model is a modified version of a VRML [Pesc94] demo file, from SGI, called the Palladio [Ferr95]).

The user interface is based on the OpenInventor [Wern94] WalkViewer, which you can get information on by clicking on the [?] icon in the right button panel.


Before doing anything else!!!

Please note that an unfortunate consequence of using the Walk Viewer is that it chooses our walking speed for us and it picks a rather poor speed for this demonstration. Therefore, before proceeding, please do the following!

At the low framerates Inventor yields with this size model, you will be glad you reduced the speed.

(Figure)

Figure A.2: Prototype User Interface


General Operation

If you type the letter H in the GreenSpace window you will see what commands are available.

Now feel free to explore the environment and look for other users. Keep an eye in the terminals where you started gsu, as that is where the simulated audio mes sages will be displayed. In order to generate simulated audio for other users to hear, you can either switch to select mode (by clicking on the arrow in the upper right hand corner of the window) and clicking on objects in the scene, or you can hit the T key while over the GreenSpace window to start generating a stream of predefined messages.

Pressing the spacebar will toggle on and off the display of the communication locality bounding boxes. Any users within those boxes are sending you position and audio data, while all others users are only reporting approximate positions to you.

(Figure)

Figure A.3: Another User in Prototype Environment

In fact, that box is really the bounding box of nine communication groups, which you are listening to all nine of and sending your data only to the group you are in (via group change announcements).

Notice that the other users' faces are grey, so that you can tell when they are looking your direction (the model for the users is a modified version of the triguy_w_shadow.wrl people found at Stonehenge [Ferr95]).

As you are wandering around the space, try to follow what a particular user is saying or doing. As the number of users increases, you should see this become increasingly difficult in the broadcast mode.

Note that it is difficult to see the point of all this when the environment is not well populated. In order to see anything of use, there should be at least one other user in the environment with you. So it would be good to ask a friend to join, or send mail to me to let me know you are entering so I can try to join you.

A.5 Feedback Request

After spending some time experimenting, please take some time to answer a few questions (see Appendix B) about your experience using this prototype!