CityWall is an interactive multitouch project open to public experimentation at the Lasipalatsi medical center in Helsinki, Finland. Developed by the Helsinki Institute for Information Technology, CityWall currently offers passers-by a 3D GUI to explore the benefits and nuisances of urban nature. It's able to recognize an unlimited number of fingers touching the screen and uniquely identify them.
Check out the video demo of CityWall after the cut
Similar to other multitouch screens we've seen, CityWall uses a rear-projection system with multiple cameras, projectors and infrared sensors. It presumably tracks reflected infrared light triggered by fingers touching the display screen, as seen in the NORTD DIY multitouch kit.
By sending SMS messages to +358505112572, users can add text comments to the display which can then be manipulated by finger-touch. Alternatively, CityWall automatically downloads and displays photos tagged with 'helsinki', 'citywall' or 'cwhki'; if an image is tagged "cwnicehki" CityWall categorizes it under "nice things", whereas the tag "cwnuishki" catageorizes the image as a nuisance.