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The Technology BehindAugmented realityAugmented Reality (AR) is a field that is primarilyconcerned with realistically adding computergeneratedimages to the image one perceivesfrom the real world.AR comes in several flavors. Best known is thepractice of using flatscreens or projectors,but nowadays AR can be experienced even onsmartphones and tablet PCs. The crux is that 3Ddigital data from another source is added to theordinary physical world, which is for exampleseen through a camera. We can create this additionaldata ourselves, e.g. using 3D drawingprograms such as 3D Studio Max, but we canalso add CT and MRI data or even live TV imagesto the real world. Likewise, animated threedimensional objects (avatars), which then can bedisplayed in the real world, can be made using avisualization program like Cinema 4D. Instead ofdisplaying information on conventional monitors,the data can also be added to the vision of theuser by means of a head-mounted display (HMD)or Head-Up Display. This is a second, less knownform of Augmented Reality. It is already knownto fighter pilots, among others. We distinguishtwo types of HMDs, namely: Optical See Through(OST) headsets and Video See Through (VST)headsets. OST headsets use semi-transparentmirrors or prisms, through which one can keepseeing the real world. At the same time, virtualobjects can be added to this view using smalldisplays that are placed on top of the prisms.VSTs are in essence Virtual Reality goggles, sothe displays are placed directly in front of youreyes. In order to see the real world, there aretwo cameras attached on the other side of thelittle displays. You can then see the AugmentedReality by mixing the video signal coming fromthe camera with the video signal containing thevirtual objects.20 21