Additional tests show high potential for VRD to be used as a display technology for patients that have low vision. In the photo at right one can see the map markers indicating runways, air traffic control tower, taxiways, and hangars overlaid on the video. The map overlays indicated the trajectories of various objects in geographic coordinates. Markerless also called instant tracking does not use marker. Virtual retinal display creates images that can be seen in ambient daylight and ambient roomlight. The most important is the position and orientation of the user's head. Computation offloading introduces new constraints in applications, especially in terms of latency and bandwidth. The computer also withdrawals from its memory to present images realistically to the onlooker. The purpose of Interaction Design is to avoid alienating or confusing the user by organising the information presented. As early as , two articles from Emergency Management magazine discussed the power of this technology for emergency management. It is important to note the two main objects in AR when developing VR applications: EyeTap[ edit ] The EyeTap also known as Generation-2 Glass  captures rays of light that would otherwise pass through the center of the lens of the eye of the wearer, and substitutes synthetic computer-controlled light for each ray of real light. A number of games were developed for prepared indoor environments, such as AR air hockey, Titans of Space, collaborative combat against virtual enemies, and AR-enhanced pool table games. It could be used to provide crucial information to a doctor or surgeon with having them take their eyes off the patient. It may also encourage tacit knowledge renewal which makes firms more competitive. To compensate for the lack of computing power, offloading data processing to a distant machine is often desired. Because the displays are not associated with each user, SAR scales naturally up to groups of users, thus allowing for collocated collaboration between users.