Augmented Reality, according to the Wikipedia, is:a term for a live direct or indirect view of a real-world environment whose elements are supplemented with-, or augmented by computer-generated imagery. The augmentation is conventionally in real-time and in meaningful context with environmental elements.
A lot of the research into AR has focused a form factor that projects annotations on to a lens (e.g. transparent shield or video feed) between the user and the actual objects. Examples include Heads-Up displays used by fighter pilots, visors or goggles, and video devices such as mobile phones or slates. In this case the user is given additional information which is projected or otherwise rendered on a lens of some kind. Look through the lens and you see the additional information.
Another form factor is to project the augmented data onto the object you are looking at. A couple of good example come from the Sixth Sense demonstration at TED this year where a keypad was projected on the users hand or meta data about the student was projected on their shirt.
A third form factor is to superimpose information onto objects in a video display. Examples of this include the 3D baseball cards and the First Down line while watching American football. The difference between augmenting a video and an augmented lens video is that you don't look through the augmented video as you do with a lens; you look at a computer monitor to television.
There is also various types of data that can be displayed. Some data, like that in a heads-up display, is monitoring information rather than supplemental information about the objects in the field of view (e.g. speed, altitude, etc.). F-16 Fighter Jet VS. Bird
Another type of information is based on location, for example the location of the nearest subway entrance or the location on which people left messages or tweets.
The third, and perhaps the most difficult to implement, is object recondition and annotation. The ability to recognize a face, or some type of object, and display associated data. This requires that the application be able to recognize faces or objects rather relying on geo-location and compass direction data as is the case with location based data.
These are all examples of different form factors and data that can be displayed in an augmented reality application. They are not mutually exclusive, but the ones that you'll be seeing the most are the augmented video and the augmented lens. Specifically there are a number of examples of mobile phone applications which provide an augmented lens.
The ReadWriteWeb.com provides a pretty good run down of different AR implementations in this article. I've also covered the topic before (here, here, hear, and hear).
The AR application I want to show today is by a company named Accrossair called, Nearest Tube, for the iPhone 3.1 OS on the 3GS version. Here is an interview with the designers that is pretty illuminating from a developers perspective.
The biggest problem with the mobile AR applications that use the lens form factor is the way in which information is presented. As we see more and more of these applications introduced, especially for the iPhone, the way in which annotations on the screen are shown will undoubtedly improve.






