Invisible digital post-it notes
February 12, 2005 In the future, cell phone users will be able to leave messages anywhere in the form of what might be termed electronic post-its. They will be able to post virtual messages referring to a specific location wherever they are needed. Siemens researchers have now created the technical basis and the computer programs for this "digital graffiti service." Post-its are exceedingly practical. They're a handy way of letting people know if you've gone out quickly to shop or to lunch, or for reminding you to do things. However, you can't stick these yellow memos in mid-air - at least not yet. But that will be possible in future with the virtual post-its from Siemens Corporate Technology's research laboratory in Munich. Dieter Kolb's team of specialists have developed computer programs that assign cell phone messages to specific locations.
The user can leave a message, known as a digital graffito, at any geographical point. This is a kind of SMS attached to one spot. When the recipient reaches the defined point, the message appears on his or her display. Unlike the classic SMS, the message is not sent to the addressee as such, but is only activated when the addressee comes within a defined radius of the location specified for the graffito.
Another difference is that, if required, the message can be read not only by one person but also by a number of cell phone users - like a real graffito plastered on a building wall. This allows a whole range of new applications, for example for special offers and advertising messages aimed at a large readership, or for making arrangements with friends.
Say, for example, that you've arranged to meet a friend for a stroll round town. While on your way you can simply leave a digital graffito, for instance at the arranged meeting point: "Just looking at a few CDs in the store opposite, come and join me."
If you wanted to send your friends the same message by SMS you would have to send every single one a separate message. This would be far more time-consuming. Advertising messages could be placed in front of stores to draw attention to special offers. Anyone in the mood for shopping could switch on the advertising mode and wander from one offer to the next. People in a hurry simply switch this mode off.
The Siemens developers have shown that the system functions with a prototype produced in cooperation with the University of Linz and the Ars Electronica Center in Linz, Germany. Ultimately the digital graffiti system is based on tried and tested communications technology and works as follows. First, the user types in the message on a mobile device, a notebook, cell phone or PDA. The message is then sent via a wireless link to a server where it is stored, assigned to the geographical point and held ready for call up.
If a person approaches the place in question the server transmits the message. That is possible because mobile phones signal their positions to the mobile control center at regular intervals. Optionally, an alerting signal can be given in the same way as with an SMS. The task facing the researchers was to develop the software for the new function.
Initially they had to create corresponding server programs for administering and forwarding the data. This form of processing messages in a mobile device and user programs of this type did not exist before. The digital graffiti also have special functions such as an expiry date. A message of the type "I'll be back in 30 minutes" can be coupled to a virtual counter, and the message is automatically erased after the set time.
If the sender is delayed he or she can access the server at any time to update their message and perhaps extend the specified time. At present it would be necessary to send a second SMS to let friends know.
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.
Digital messages can 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.