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Plate 2: Three users represented by different avatars <strong>in</strong> a multi-user VRML world<br />

Our extensions to VRML <strong>in</strong> order to support avatars, <strong>in</strong>fluence several aspects of user representations:<br />

the current avatar of the user<br />

alternative avatars of the user<br />

the user-specific and avatar-specific behavior<br />

groups the user belongs to<br />

navigation and camera sett<strong>in</strong>gs for the user and/or a s<strong>in</strong>gle avatar<br />

items which belong to the user or avatar, but are not visible to other participants (belong<strong>in</strong>gs)<br />

items the user or avatar is carry<strong>in</strong>g<br />

Each user needs a unique identifier, <strong>in</strong>dependent of the local virtual world. This is necessary <strong>in</strong> order to support user<br />

movements between different worlds (a user has to be identified as a certa<strong>in</strong> user rather than just a user). A simple<br />

convention to achieve this, would be to use the user's email address or a user@host scheme as used for talk. Although<br />

users without avatars are not very useful <strong>in</strong> multi-user virtual worlds, we need to represent certa<strong>in</strong> aspects of a user<br />

which are <strong>in</strong>dependent or at least might be <strong>in</strong>dependent of the currently selected avatar. Beside the user's id this <strong>in</strong>cludes<br />

the current location of the user (represented by a 3D trans<strong>format</strong>ion), his groups and avatar <strong>in</strong>dependent behaviors,<br />

items, and belong<strong>in</strong>gs. Groups can be used to def<strong>in</strong>e certa<strong>in</strong> rights and/or restrictions for several users, <strong>in</strong>dependent of<br />

their <strong>in</strong>dividual id. A user might participate <strong>in</strong> several groups.

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