This paper describes how to instrument the physical world so that objects become self-describing, communicating their identity, geometry, and other information such as history or user annotation. The enabling technology is a wireless tag which acts as a radio frequency identity and geometry (RFIG) transponder. We show how addition of a photo-sensor to a wireless tag significantly extends its functionality to allow geometric operations -such as finding the 3D position of a tag, or detecting

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... e in the shape of a tagged object. Tag data is presented to the user by direct projection using a handheld locale-aware mobile projector. We introduce a novel technique that we call interactive projection to allow a user to interact with projected information e.g. to navigate or update the projected information. The ideas are demonstrated using objects with active radio frequency (RF) tags. But the work was motivated by the advent of unpowered passive-RFID, a technology that promises to have significant impact in real-world applications. We discuss how our current prototypes could evolve to passive-RFID in the future.