A Guide To VR

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Head Mounted Displays

Head Mounted Displays are the most common and in many ways the most practical way of experiencing virtual reality. As the name suggests, Head Mounted Displays (HMDs) are display devices worn on your head, like a helmet or goggles. They typically obscure your view from the real world entirely and feature one display for each eye to project a stereoscopic image onto. Tracking is either done inside the device, or via an external tracking system. Below is an extensive list of considerations for choosing a head mounted display to use for your VR applications.

Display

Resolution

Resolution is the amount of pixels the display is made out of. The higher the resolution, the more detail can be shown. However, a higher resolution requires more processing power and bandwidth.

Display Technology

Displays can be made in different ways. The most common display types are OLED and LCD. The display type influences the brightness, vibrance and contrast of the image. OLED displays typically have a better contrast with lower black values, but there is often more space between individual pixels, which can result in a more prominent screen-door effect. Also, the higher the refresh rate of the display, the better.

Lens Technology

See this article

Field of View

Field of view (FOV) is usually defined as the angle of your cone of vision inside the head mounted display. A larger field of view can increase the feeling of immersion, but it also means spreading the available resolution over a larger area, resulting in a lower level of detail. Most consumer head mounted displays have found the best balance to be around 90-100 degrees. Note: FOV is heavily influenced by the distance between your eyes and the lenses and there is no standardized way to measure it, so manufacturer specifications should be taken with a grain of salt.

Audio

Speakers

Many of the modern head mounted displays come with their own audio solutions, either through built-in speakers or flip-down headphones. Of course closed-back circumaural headphones provide better isolation from your environment and more bass than small integral speakers.

Microphone

Most of the modern head mounted displays also come with a built-in microphone, which allows for verbal communication in multi-player or speech-processing applications.

Tracking

Degrees of Freedom

Degrees of freedom (DOF) is the number of dimensions in which your head mounted display (and other trackables) are tracked. For VR, this simply comes down to the distinction between 3DOF (rotation only) and 6DOF (rotation + position). Without position tracking, the image stays static relative to the head mounted display, which can cause some nausea when you move your head but your eyes don't register a shift in perspective. Also the level of interaction possible with a 3DOF hand controller is much more limited than a 6DOF controller.

Area/Volume

The type of tracking system dictates the size of the area/volume a user can move around in. Many consumer VR devices make the distinction between standing/seated (limited body movement) and "room-scale" (typically around 16m2). With inside-out tracking or a large external tracking system, even greater areas could be covered, giving the user more freedom to walk around as they would in real life. When the tracking area is limited, applications have to resort to other means of transport, for instance teleportation.