Ambient intelligence, distributed agent systems, smart buildings and other emerging architectures leave the user lost between large amounts of autonomous entities or agents. With agents in cars, personal devices and other mobile systems, the set of agents available to the user can change rapidly, adding to the problems. We propose a set of agent relations to organize agents in an ad hoc situation. There are dynamic task-, location- and user relations, creating multiple relation hierarchies in agent space. These hierarchies allow robust, space- and task limited, context-sensitive search through agent space. We show how to use this structure to keep user interfaces near the user, and how it can be used to support the user in finding the agent he needs in a context-sensitive way.

We present a client/server implementation for running demanding mobile AR application on a PDA device. The system incorporates various data compression methods to make it run as fast as possible on a wide range of communication networks, from GSM to WLAN.

A mathematical model is presented for comparing geometric and image-based simplification methods. Geometric simplification reduces the number of polygons in the virtual object and image-based simplification replaces the object with an image. Our model integrates and extrapolates existing accuracy estimates, enabling the comparison of different simplification methods in order to choose the most efficient method in a given situation. The model compares data transfer and rendering load of the methods. Byte size and expected lifetime of simplifications are calculated as a function of the desired visual quality and the position and movement of the viewer. An example result is that, in typical viewing and rendering conditions and for objects with a radius in the order of one meter, imposter techniques can be used at viewing distances above 15 meters. Below that, simplified polygon objects are required and, below one meter distance, the full-resolution virtual object has to be rendered. An electronic version of the model is available on the web.