Bimber and Raskar offer a brief introduction to augmented reality in regards to what it actually is, its relationship to virtual reality, what technology exists to support it, how it might be used and what constraints there are in terms of achieving augmented reality. They begin their definition of augmented reality by explaining that it is not, in fact, a virtual environment. In a virtual environment, our senses are controlled by the computer – ie. there is no ‘real environment’, it is synthetic. In augmented reality, the real environment exists and plays a key role, and synthetic components are embedded in. They argue that this paves the way for problems to arise, however, since the real world is difficult to control (particularly when compared to a synthetic one). The list ‘tracking’ and ‘registration’ as being the two important steps to combating these problems. They list various tracking options, but list markerless tracking as being the most promising (if not the more difficult) option for AR, since it eliminates the need for existing markers in the real world and will only improve with advancements in mobile and camera technology, as well as GPS tracking. In terms of displaying this information, they acknowledge headsets as being a popular choice for AR projects, however they suggest it still has too many limitations in regards to cost, accessibility and human factors such as it putting a strain on participants. It’s also more commonly used for VR, and AR might more closely align with live or mobile experiences.