Invisible digital post-it notes

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A focal point of the research work was to develop different ways of displaying digital graffiti. For the specialists it was a matter of particular importance to use standard commercial devices to enable the new message system to be implemented quickly.

As it turned out, a mobile phone with camera function and a very few add-on devices are sufficient to make the messages visible not just in written form but also in a photo of the vicinity. The really clever trick is that the virtual messages are superimposed on the real world (Augmented Reality (AR)).

The user can take a picture of the surroundings with a mobile phone camera. The digital graffito is then superimposed on the camera photo. One possible use for this function would be for applications in tourism. Digital messages could be attached to pictures of a local sight to provide information about the building.

The radius in which the message can be received can be selected by the writer of the message. Buildings visible from far off - the Acropolis in Athen, for instance - can be given a larger radius of a few miles enabling tourists to read the graffito as well from a long way away.

In order to superimpose the corresponding graffito correctly the mobile terminal device naturally has to know where it is located at any particular moment, and in the case of an AR display it must also know in what direction the camera is held. For this purpose the researchers coupled the device with a GPS receiver which ascertains the position to an accuracy of a few meters by means of satellite positioning.

They also linked a tiny device the size of a matchbox that determines the position three-dimensionally by means of a small electronic compass and an acceleration sensor. The upgraded cell phone then knows exactly where it is and which way it is pointing and can thus superimpose the received graffiti exactly on the live photo.

Naturally, the graffiti process can also be used in closed rooms in which reception of signals from GPS satellites is impossible. In this case different methods are applied to determine the position. A mobile terminal can be used to receive and display graffiti in museums as background information to a painting, for instance.

The connection to a server can be set up in such cases using wireless standards such as WLAN, Bluetooth or GPRS. At present the developers anticipate that the graffiti system will be rolled out in about two years time, most likely starting with applications for tourism and in the exhibition sector.

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