head a headmounted display or helmet mounted display for aviation applications both abbreviated hmd is a display device worn on the head or as part of a helmet that has a small display optic in front of one monocular hmd or each eye binocular hmd a hmd has many uses including in gaming aviation engineering and medicine there is also an optical headmounted display ohmd which is a wearable display that can reflect projected images and allows a user to see through it a binocular headmounted display hmd a professional headmounted display hmd a man controls google glass a type of peripheral headmounted display using the touchpad built into the side of the device the oculus rift virtual reality headset a htc vive headset overview a typical hmd has one or two small displays with lenses and semitransparent mirrors embedded in eyeglasses also termed data glasses a visor or a helmet the display units are miniaturised and may include cathode ray tubes crt liquid crystal displays lcds liquid crystal on silicon lcos or organic lightemitting diodes oled some vendors employ multiple microdisplays to increase total resolution and field of view hmds differ in whether they can display only computergenerated imagery cgi or only live imagery from the physical world or combination most hmds can display only a computergenerated image sometimes referred to as virtual image some hmds can allow a cgi to be superimposed on realworld view this is sometimes referred to as augmented reality or mixed reality combining realworld view with cgi can be done by projecting the cgi through a partially reflective mirror and viewing the real world directly this method is often called optical seethrough combining realworld view with cgi can also be done electronically by accepting video from a camera and mixing it electronically with cgi this method is often called video seethrough optical hmd optical headmounted display an optical headmounted display uses an optical mixer which is made of partly silvered mirrors it can reflect artificial images and let real images cross the lens and let a user look through it various methods have existed for seethrough hmds most of which can be summarized into two main families based on curved mirrors or waveguides curved mirrors have been used by laster technologies and by vuzix in their star 1200 product various waveguide methods have existed for years these include diffraction optics holographic optics polarized optics and reflective optics applications major hmd applications include military government fire police etc and civiliancommercial medicine video gaming sports etc aviation and tactical ground helmet mounted display in 1962 hughes aircraft company revealed the electrocular a compact crt7 long headmounted monocular display that reflected a tv signal in to transparent eyepiece ruggedized hmds are increasingly being integrated into the cockpits of modern helicopters and fighter aircraft these are usually fully integrated with the pilots flying helmet and may include protective visors night vision devices and displays of other symbology military police and firefighters use hmds to display tactical information such as maps or thermal imaging data while viewing a real scene recent applications have included the use of hmd for paratroopers the defense advanced research projects agency darpa continues to fund research in augmented reality hmds as part of the persistent close air support pcas program vuzix is currently working on a system for pcas that will use holographic waveguides to produce seethrough augmented reality glasses that are only a few millimeters thick engineering engineers and scientists use hmds to provide stereoscopic views of computeraided design cad schematics virtual reality when applied to engineering and design is a key factor in integration of the human in the design by enabling engineers to interact with their designs in full lifesize scale products can be validated for issues that may not have been visible until physical prototyping the use of hmds for vr is seen as supplemental to the conventional use of cave for vr simulation hmds are predominantly used for singleperson interaction with the design while caves allow for more collaborative virtual reality sessions head mounted display systems are also used in the maintenance of complex systems as they can give a technician a simulated xray vision by combining computer graphics such as system diagrams and imagery with the technicians natural vision augmented or modified reality medicine and research there are also applications in surgery wherein a combination of radiographic data xray computed tomography cat scans and magnetic resonance imaging mri imaging is combined with the surgeons natural view of the operation and anesthesia where the patient vital signs are within the anesthesiologists field of view at all times an eye tracking hmd with led illuminators and cameras to measure eye movementsresearch universities often use hmds to conduct studies related to vision balance cognition and neuroscience as of 2010 the use of predictive visual tracking measurement to identify mild traumatic brain injury was being studied in visual tracking tests a hmd unit with eye tracking ability shows an object moving in a regular pattern people without brain injury are able to track the moving object with smooth pursuit eye movements and correct trajectory gaming and video see also virtual reality headset disney hmd mount low cost hmd devices are available for use with 3d games and entertainment applications one of the first commercially available hmds was the forte vfx1 which was announced at consumer electronics show ces in 1994 the vfx1 had stereoscopic displays 3axis headtracking and stereo headphones another pioneer in this field was sony which released the glasstron in 1997 it had as an optional accessory a positional sensor which permitted the user to view the surroundings with the perspective moving as the head moved providing a deep sense of immersion one novel application of this technology was in the game mechwarrior 2 which permitted users of the sony glasstron or virtual ios iglasses to adopt a new visual perspective from inside the cockpit of the craft using their own eyes as visual and seeing the battlefield through their crafts own cockpit as of 2013 many brands of video glasses can be connected to video and dslr cameras making them applicable as a new age monitor as a result of the glasses ability to block out ambient light filmmakers and photographers are able to see clearer presentations of their live images the oculus rift is a virtual reality vr headmounted display created by palmer luckey that the company oculus vr is developing for virtual reality simulations and video games sports a hmd system has been developed for formula one drivers by kopin corp and the bmw group according to bmw the hmd is part of an advanced telemetry system approved for installation by the formula one racing committee to communicate to the driver wirelessly from the heart of the race pit the hmd will display critical race data while allowing the driver to continue focusing on the track pit crews control the data and messages sent to their drivers through twoway radio recon instruments released on 3 november 2011 two head mounted displays for ski goggles mod and mod live the latter based on an android operating system training and simulation paratrooper training with an hmd a key application for hmds is training and simulation allowing to virtually place a trainee in a situation that is either too expensive or too dangerous to replicate in reallife training with hmds covers a wide range of applications from driving welding and spray painting flight and vehicle simulators dismounted soldier training medical procedure training and more however a number of unwanted symptoms have been caused by prolonged use of certain types of headmounted displays and these issues must be resolved before optimal training and simulation is feasible performance parameters ability to show stereoscopic imagery a binocular hmd has the potential to display a different image to each eye this can be used to show stereoscopic images it should be borne in mind that socalled optical infinity is generally taken by flight surgeons and display experts as about 9 metres this is the distance at which given the average human eye rangefinder baseline distance between the eyes or interpupillary distance ipd of between 25 and 3inches 6 and 8cm the angle of an object at that distance becomes essentially the same from each eye at smaller ranges the perspective from each eye is significantly different and the expense of generating two different visual channels through the computergenerated imagery cgi system becomes worthwhile interpupillary distance ipd this is the distance between the two eyes measured at the pupils and is important in designing headmounted displays field of view fov humans have an fov of around 180 but most hmds offer far less than this typically a greater field of view results in a greater sense of immersion and better situational awareness most people do not have a good feel for what a particular quoted fov would look like eg 25 so often manufacturers will quote an apparent screen size most people sit about 60cm away from their monitors and have quite a good feel about screen sizes at that distance to convert the manufacturers apparent screen size to a desktop monitor position divide the screen size by the distance in feet then multiply by 2 consumerlevel hmds typically offer a fov of about 3040 whereas professional hmds offer a field of view of 60 to 150 resolution hmds usually mention either the total number of pixels or the number of pixels per degree listing the total number of pixels eg 16001200 pixels per eye is borrowed from how the specifications of computer monitors are presented however the pixel density usually specified in pixels per degree or in arcminutes per pixel is also used to determine visual acuity 60 pixels 1 arcminpixel is usually referred to as eye limiting resolution above which increased resolution is not noticed by people with normal vision hmds typically offer 10 to 20 pixels though advances in microdisplays help increase this number binocular overlap measures the area that is common to both eyes binocular overlap is the basis for the sense of depth and stereo allowing humans to sense which objects are near and which objects are far humans have a binocular overlap of about 100 50 to the left of the nose and 50 to the right the larger the binocular overlap offered by an hmd the greater the sense of stereo overlap is sometimes specified in degrees eg 74 or as a percentage indicating how much of the visual field of each eye is common to the other eye distant focus collimation optical methods may be used to present the images at a distant focus which seems to improve the realism of images that in the real world would be at a distance onboard processing and operating system some hmd vendors offer onboard operating systems such as android allowing applications to run locally on the hmd and eliminating the need to be tethered to an external device to generate video these are sometimes referred to as smart goggles to make the hmd construction lighter producers may move the processing system to connected smart necklace formfactor that would also offer the additional benefit of larger battery pack such solution would allow to design lite hmd with sufficient energy supply for dual video inputs or higher frequency timebased multiplexing see below support of 3d video formats frame sequential multiplexing sidebyside and topbottom multiplexing depth perception inside an hmd requires different images for the left and right eyes there are multiple ways to provide these separate images use dual video inputs thereby providing a completely separate video signal to each eye timebased multiplexing methods such as frame sequential combine two separate video signals into one signal by alternating the left and right images in successive frames side by side or topbottom multiplexing this method allocated half of the image to the left eye and the other half of the image to the right eye the advantage of dual video inputs is that it provides the maximum resolution for each image and the maximum frame rate for each eye the disadvantage of dual video inputs is that it requires separate video outputs and cables from the device generating the content timebased multiplexing preserves the full resolution per each image but reduces the frame rate by half for example if the signal is presented at 60hz each eye is receiving just 30hz updates this may become an issue with accurately presenting fastmoving images sidebyside and topbottom multiplexing provide fullrate updates to each eye but reduce the resolution presented to each eye many 3d broadcasts such as espn chose to provide sidebyside 3d which saves the need to allocate extra transmission bandwidth and is more suitable to fastpaced sports action relative to timebased multiplexing methods not all hmds provide depth perception some lowerend modules are essentially biocular devices where both eyes are presented with the same image 3d video players sometimes allow maximum compatibility with hmds by providing the user with a choice of the 3d format to be used peripherals the most rudimentary hmds simply project an image or symbology on a wearers visor or reticle the image is not slaved to the real world ie the image does not change based on the wearers head position more sophisticated hmds incorporate a positioning system that tracks the wearers head position and angle so that the picture or symbology displayed is congruent with the outside world using seethrough imagery head tracking slaving the imagery headmounted displays may also be used with tracking sensors that detect changes of angle and orientation when such data is available in the system computer it can be used to generate the appropriate computergenerated imagery cgi for the angleoflook at the particular time this allows the user to look around a virtual reality environment simply by moving the head without the need for a separate controller to change the angle of the imagery in radiobased systems compared to wires the wearer may move about within the tracking limits of the system eye tracking eye trackers measure the point of gaze allowing a computer to sense where the user is looking this information is useful in a variety of contexts such as user interface navigation by sensing the users gaze a computer can change the information displayed on a screen bring added details to attention etc hand tracking tracking hand movement from the perspective of the hmd allows natural interaction with content and a convenient gameplay mechanism virtual reality headset virtual reality vr augmented reality ar computermediated reality eyetap headup display hud smartglasses helmet mounted display lumusoptical mixed reality mr positioning technologies screenless stereoscopy virtual retinal display list of optical headmounted display manufacturers bibliography head mounted displays designing for the user melzer and moffitt mcgraw hill 1997 o cakmakci and jp rolland headworn displays a review ieee journal of display technology vol 2 no 3 september 2006 vtemixed and virtual realityconcepts virtuality virtual cinematography augmented reality augmented virtuality real life projection augmented model realityvirtuality continuum artificial reality simulated reality ubiquitous computing virtual world persistent multimodal interaction telepresence immersion technology haptic suit wearable computer omnidirectional treadmill display headmounted display optical headup display virtual retinal display virtual reality headset stereoscopy computer vision stereo camera camera resectioning omnidirectional camera software compositing imagebased modeling and rendering realtime computer graphics visual hull chroma key hidden surface determination photography free viewpoint television 360degree video vr photography tracking motion capture tracking system types optical inertial devices wired glove gametrak google glass microsoft hololens playstation move leap motion kinect sixense truemotion immersivedevicespersonal merge vr ar daydream google cardboard htc vive oculus rift samsung gear vr playstation vr pimax osvr magic leap rooms allosphere cave treadport history sensorama virtual boy famicom 3d system sword of damocles sega vr virtuality applications pervasive game artoolkit arcore interactive art virtual graffiti simulated reality in fiction vtestereoscopyperception binocular rivalry binocular vision chromostereopsis convergence insufficiency correspondence problem peripheral vision depth perception epipolar geometry kinetic depth effect stereoblindness stereopsis stereopsis recovery stereoscopic acuity displaytechnologies active shutter 3d system anaglyph 3d autostereogram autostereoscopy bubblegram chromadepth headmounted display holography integral imaging lenticular lens multiscopy parallax barrier parallax scrolling polarized 3d system specular holography stereo display stereoscope vectograph virtual retinal display volumetric display wiggle stereoscopy othertechnologies 2d to 3d conversion 2d plus delta 2dplusdepth computer stereo vision multiview video coding parallax scanning pseudoscope stereo photography techniques stereoautograph stereoscopic depth rendition stereoscopic rangefinder stereoscopic spectroscopy stereoscopic video coding producttypes 3d camcorder 3d film 3d television 3denabled mobile phones 4d film bluray 3d digital 3d stereo camera stereo microscope stereoscopic video game virtual reality headset notableproducts amd hd3d dolby 3d fujifilm finepix real 3d infitec masterimage 3d nintendo 3ds new 3ds nvidia 3d vision panavision 3d reald 3d sharp actius rd3d viewmaster xpand 3d miscellany international stereoscopic union stereographer stereoscopic displays and applications vteheadwearhatscapsgeneral asian conical baseball beanie beret boater bonnet bowler bucket casquette cowboy cricket easter fedora trilby fez flat gandhi homburg anthony eden knit kofia newsboy pillbox pork pie sombrero stormy kromer straw sun top opera tricorne trucker ushanka military bearskin boonie campaign forage mitznefet peaked sailor side utility cover wrapped dorag hood turban veil crowns andbands astral circlet consort corolla coronation coronet diadem eastern ferronnire fillet hoop imperial makua queens state tiara wreathlaurel helmetscombat corinthian imperial barbute close great morion sallet advanced combat enhanced combat us flight mk 7 paratrooper stahlhelm vocational firefighter hard hat welding sport batting bicycle football motorcycle racing other protective balaclava earmuffs earplug face shield facekini padded headgear scarf sports visor eyewear eyeglasses pincenez browline gi rimless monocle goggles sunglasses headmounted display hairwear andother items barrette deely bobber dushtoh hair drop hair tie hairnet headband headphones headpiece kerchief peineta scrunchie shpitzel list of headwear vteemerging technologiesfieldsagriculture agricultural robot closed ecological systems cultured meat genetically modified food precision agriculture vertical farming architecture arcology building printing contour crafting domed city biomedical artificial uterus ampakine brain transplant cryonics cryoprotectant cryopreservation vitrification suspended animation deextinction genetic engineering gene therapy head transplant isolated brain life extension strategies for engineered negligible senescence nanomedicine nanosensors organ printing personalized medicine regenerative medicine stemcell therapy tissue engineering robotassisted surgery synthetic biology synthetic genomics virotherapy oncolytic virus tricorder whole genome sequencing displaysnext generation fed flcd imod laser lpd oled olet qdled sed tpd tdel tmos screenless bionic contact lens headmounted display headup display optical headmounted display virtual retinal display other autostereoscopy flexible display holographic display computergenerated holography multiprimary color display ultra hd volumetric display electronics electronic nose etextiles flexible electronics molecular electronics nanoelectromechanical systems memristor spintronics thermal copper pillar bump energyproduction airborne wind turbine artificial photosynthesis biofuels carbonneutral fuel concentrated solar power fusion power home fuel cell hydrogen economy methanol economy molten salt reactor nantenna photovoltaic pavement spacebased solar power vortex engine storage beltway battery compressed air energy storage flywheel energy storage grid energy storage lithiumair battery moltensalt battery nanowire battery research in lithiumion batteries siliconair battery thermal energy storage ultracapacitor other smart grid 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nanomaterials picotechnology programmable matter quantum dots silicene superalloy synthetic diamond military antimatter weapon caseless ammunition directedenergy weapon laser maser particlebeam weapon sonic weapon coilgun railgun plasma weapon pure fusion weapon stealth technology vortex ring gun neuroscience artificial brain braincomputer interface electroencephalography mind uploading brainreading neuroinformatics neuroprosthetics bionic eye brain implant exocortex retinal implant quantum quantum algorithms quantum amplifier quantum bus quantum channel quantum circuit quantum complexity theory quantum computing quantum cryptography quantum dynamics quantum electronics quantum error correction quantum imaging quantum information quantum key distribution quantum logic quantum logic gates quantum machine quantum machine learning quantum metamaterial quantum metrology quantum network quantum neural network quantum optics quantum programming quantum sensing quantum simulator quantum teleportation robotics domotics nanorobotics powered exoskeleton selfreconfiguring modular robot swarm robotics uncrewed vehicle space sciencelaunch fusion rocket nonrocket spacelaunch mass driver orbital ring skyhook space elevator space fountain space tether reusable launch system propulsion beampowered propulsion ion thruster laser propulsion plasma propulsion engine helicon thruster vasimr nuclear pulse propulsion solar sail other interstellar travel propellant depot laser communication in space transportaerial adaptive compliant wing backpack helicopter delivery drone flying car highaltitude platform jet pack pulse detonation engine scramjet spaceplane supersonic transport land airless tire alternative fuel vehicle hydrogen vehicle driverless car ground effect train hyperloop maglev train personal rapid transit transit elevated bus vactrain vehicular communication systems pipeline pneumatic transport automated vacuum collection other antigravity cloak of invisibility digital scent 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