Virtual graffiti

This set of use cases is centered on a mobile user receiving or sending a message based on the computed location of the user. These include experiences such as

• A mobile user poses a query where the nearest Italian restaurant is and receives a set of messages and coupons from nearby restaurant proprietors.
• A user receives a message on her phone that there is an accident on the road a few miles ahead along with a suggested alternative route to take.
• Coworkers arrive in a conference room and receive a notification that the meeting has been moved to a new location.

These use cases are important because they serve as a basis from which the other use cases are built. The resolution of the messaging content is directly related to the accuracy with which the location can be computed.

This involves anchoring a virtual reality experience at a physical location. Thus the experiences in the virtual world can only be had at a specific real location. Several use cases that are included here are

• A virtual command post can be set up at the scene of an incident. This command post involves the sharing of information in the virtual world but can only be accessed by those at the scene of the incident.
• A set of blogs and media files are left at famous outdoor sculptures. Groups of friends can contribute, copy, and share files only while they are viewing the sculpture.

Contextual messaging refers to leaving some type context-specific annotation, e.g. a virtual post-it note on a computer monitor, a time-sensitive message attached to a conference room telling the occupants you won’t be attending a meeting or location-based graffiti on a physical object.

Researchers at the University of Salford experimented with a CAVE system[1] in which a user could mark up a scene using 6-degree of freedom sensors. Obviously this is not something that is suitable for immediate use or mass market applications, but it serves as starting point from which other work could be derived.

Kit Hughes, during a research fellowship at the University of Georgia in 2003, developed a system in which users with WiFi-enabled mobile devices could mark up buildings in downtown Athens, Georgia with their own virtual graffiti via a process known as tagging.[2] In this system, the buildings are selected on a map and the graffiti is stored in a database where it can be accessed from other mobile devices and the project’s website.

A location-based messaging system[3] for leaving virtual post-it notes on physical objects was developed at the National University of Singapore. The system uses mobile devices as AR interfaces to view virtual messages associated with fiducial markers on physical objects.

In a project from Lancaster University,[4] mobile phones are used as digital spray cans. RFID tags are used to identify objects that can be marked up. The RFID tags can hold the identities of the last five people to leave graffiti. The graffiti itself is stored on a server indexed by RFID tag. When another user comes within range of an RFID-tagged object, the graffiti associated with that object is downloaded into their mobile device.