As mentioned earlier, virtual reality-head-mounted displays, are categorized as close HMDs and sub-divided into those with an integrated or built-in dedicated display (e.g., Oculus, HTV Vive), and smartphone display (e.g., Samsung Gear). A VHMD completely occludes the user’s view of the outside world and immerses him or her in the virtual world.
Likewise, augmented reality-head-mounted displays, which are close HMDs, are sub-divided into data and graphics. Data augmented reality head-mounted displays are those devices that only deliver information in the form of data (i.e., text and very primitive graphics objects such as a box or triangle) and graphics. Graphics augmented reality-head-mounted displays deliver complex computer-generated graphics data, such as engineering drawings, maps, or entertainment.
Augmented reality-head-mounted displays come in the form of helmets, can be data-only or graphics capable, and glasses (also known as smart-glasses). Augmented reality can also be delivered to tablets and smartphones that have forward-facing cameras. When augmented reality is used on such handheld devices, (which could include notebook computers), they are sometimes referred to as see-through or “Windows on the World” (WOW) systems.
Traditional user interfaces (UIs) for “off-the-desktop” applications display the digital information on flat 2D surfaces. Spatially augmented reality (SAR) uses projectors to display on walls, or a table top that a user can interact with without a head-mounted display or handheld device. It is like a CAVE (Cave Automatic Virtual Environment—a virtual reality environment consisting of a cube -shaped room in which the walls are rear-projection screens) but lacks the physical 3D aspect of a CAVE.