Knowledge Base /H /HMD
HMD
Knowledge Base → HHMD (Head-mounted display or Helmet mounted display) is a display device used in immersive virtual reality. It is worn on a head or as part of a helmet that has a small display optic in front of one eye (monocular) or each eye (binocular).
A typical HMD has either one or two small displays with lenses and semi-transparent mirrors embedded in a helmet, eye-glasses (also known as data glasses) or visor. The display units are miniaturised and may include CRT, LCDs, Liquid crystal on silicon (LCos), or OLED. Some vendors employ multiple micro-displays to increase total resolution and field of view.
To achieve a stereoscopic effect, the user typically wears a helmet or glasses with two small LCD or OLED displays with magnifying lenses, one for each eye. A separate video source is displayed in front of each eye.
HMDs differ in whether they can display just a computer generated image (CGI), show live images from the real world or a combination of both.
Most HMDs display only a computer-generated image, sometimes referred to as a virtual image
Head-mounted or wearable glasses may be used to view a see-through image imposed upon the real world view, creating what is called augmented reality. This is done by reflecting the video images through partially reflective mirrors. The real world view is seen through the mirrors' reflective surface. Experimental systems have been used for gaming, where virtual opponents may peek from real windows as a player moves about. This type of system is expected to have wide application in the maintenance of complex systems, as it can give a technician what is effectively «x-ray vision» by combining computer graphics rendering of hidden elements with the technician's natural vision. Additionally, technical data and schematic diagrams may be delivered to this same equipment, eliminating the need to obtain and carry bulky paper documents.
HMDs may also be coupled with head-tracking devices, allowing the user to «look around» the virtual world by moving their head, eliminating the need for a separate controller. Performing this update quickly enough to avoid inducing nausea in the user requires a great amount of computer image processing. If six axis position sensing (direction and position) is used then wearer may move about within the limitations of the equipment used. Owing to rapid advancements in computer graphics and the continuing miniaturization of video and other equipment these devices are beginning to become available at more reasonable cost.
