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Abstract:The paper presents a design methodology and a case study for monocular headmounted displays (HMDs), wherein a user can simultaneously and easily see the physical world by looking through and/or around the display. The design approach is user-focused because of the complexity of the human visual system, and because HMDs are very task, user, and context specific. A literature review of factors related to HMD design is given. This includes considerations for basic optical design, the human visual system, and head and neck biomechanics. General HMD design guidelines are given based on these considerations. For the specific case study on fire-fighting, it is recommended that the HMD be mounted at 15• to 45• below the Frankfurt plane, with a 15• to 40• field of view. A resolution of 20-60 px/deg should be focused at 1 m or farther. The neck joint torque due to the HMD should not exceed about 1 Nm. This equates to a typical maximum weight of 0.5 to 1 kg depending on the mounting location.

A custom head-mounted display (HMD) integrated into a firefighter's facemask was evaluated for its ability to aid in navigating through large buildings in low-visibility conditions. The HMD was a monocular occluded design with a colour 640 × 480 pixel LCD mounted low in one's field of view. It showed the subject their real-time location on a floor plan. Subject location was found with an 802.15.4 wireless sensor network by using the received signal strength indicator localization method. The study consisted of two different courses of similar difficulty in different buildings in the campus of the University of California, Berkeley. There were 21 subjects, of which eight of them were firefighters and five of them were female. The subjects completed the courses in the same order, but alternated in treatment condition. Subjects with the HMD returned on average a 38 per cent faster course completion time, a 44 per cent shorter distance travelled, 60 per cent fewer navigation errors, and 60 per cent more accurate map marking. A follow-up questionnaire showed a strong preference for use of the HMD in navigation tasks, and unanimous approval of the occluded optical design and low mounting location.