Here I’m collecting a list of terms and definitions which are often used in discussing virtual reality, augmented reality, head mounted displays, and more. This is a work in progress and will be updated as time goes on.

  • 3D 3Dimensional: An umbrella term which describes stereoscopic video playback which gives the viewer the illusion of three-dimensional space (depth) from a two-dimensional display. Because human eyes are separated by several centimeters, each eye sees a slightly different image. Animals with two eyes facing in the same direction create a sense of depth (sometimes called depth perception) by synthesizing the subtle differences between the image viewed by each eye. This is known as parallax. In order for 3D displays to work, the display must provide a different image to each eye. On an HMD, this is accomplished by simply having one screen for each eye. On a 3D HDTV, this is often accomplished by using polarized glasses which separate the incoming light from the screen causing some of it to go to one eye and some of it to go to the other. As long as a display is capable of sending one set of images to the left eye, and independently sending another set of images to the right eye, then a 3D effect is possible. See more about the history of 3D and stereoscopy here.
  • Exit-pupil: This describes the ‘sweet spot’ of a head mounted display where the image is fully in focus. A small exit-pupil would mean that only a small potion of the overall display is in focus. A large exit-pupil (preferred) means that more of the viewable area will be in focus. See more about exit-pupil here.
  • FoV — Field of View: Describes the angular distance of what is visible. This term is often applied to HMDs to describe how much of one’s vision is taken up by the display. A small FoV would mean that only a small portion of one’s vision is taken up by the display, while a large FoV would mean that the majority of one’s vision is taken up by the display. A fully immersive display would have an FoV that meets or exceeds the natural FoV of the human eye. A display with such an FoV would appear to completely surround the viewer — a desired attribute for highly immersive virtual reality simulations, but one that has not been readily achieved in consumer-available HMDs as of this writing. See more about Field of View here.
  • HCI — Human-Computer Interaction: Refers to the study and process by which humans interact with computers. Very basic HCI is something as simple as a keyboard and mouse while advanced HCI could be thought-controlled interactions between a person and a computer. See more about Human-Computer Interaction here.
  • Head-Tracking — Using some system to track the direction that a person’s head is turning and use it as a form of input. This term is most commonly used in conjunction with HMDs as the head-tracking data is used to adjust the images on the screen as the head moves to give the illusion of a complete world surrounding the wearer of the HMD.
  • HUD — Heads Up Display: An image projected on top of a scene, often with the goal of providing relevant and contextual information about the scene. You’ve likely seen a HUD in a videogame where health, ammunition, weapon selection, and other information is shown. HUDs can also be found in the real world and are commonly used in aircraft to provide airspeed, heading, horizon-tracking, and other important information, without the need for the pilot to look away from the scene. See more about Heads Up Displays here.
  • HMD — Head Mounted Display: Almost identical in concept to a TV, except an HMD is worn directly on the head with a small screen placed in front of each eye. Because of the form-factor, HMDs can only be used by one person at a time. Because HMDs are ‘stereo’ (dual) displays (there is one screen for each eye), all HMDs are inherently capable of 3D display, as long as it is possible to display different images on each display. See more about HMDs here.
  • IPD — Interpupillary Distance: The distance between the pupils of your eyes. This is an important factor in HMDs as misaligned IPD can result in blurry images and poor 3D effects. Most HMDs are designed with an adjustable IPD to accommodate varying facial structures and eye spacing. See more about IPD here.
  • VARVariable Acuity Resolution: Placing more pixels in the center of the eye than on the sides to mimic the natural way that the eye sees. This is often achieved with optics to bend an image to create the effect.

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