The IRREAL system is a building information system that by its pure working principle can also be used as a navigation system within buildings. It is based on the Palm Pilot family of PDAs most of which feature a builtin infrared port located in the middle of the top end of the device, so that it points away from the user when the device is being held in front of the user. By using this port to receive data from strong infrared transmitters located in strategically important places of a building the PDAs can display localized information within the range of these senders. Since each sender is broadcasting different information, the mobile devices seemingly become location aware, or seen from a different point of view, they make visible the data from the infrared data stream that effectively augments this area of the building. In this way it is possible to attach information to certain places such as offices or segments of a hallway. Since no explicit tracking is involved all the problems connected to wide range tracking can be ignored and the devices can be kept extremely light weight.