Environmental Engineering Reference
In-Depth Information
Fig. 1. Visette 45 SXGA head mounted display (HMD)
Small CRT
head mounted display uses two CRTs that are positioned on the side of the
HMD. Mirrors are used to direct the scene to the viewers' eye. Unlike the projected HMD
where the phosphor is illuminated by fiber optic cables, here the phosphor is illuminated by
an electron gun as usual (Lane, 1993). CRT
head mounted display is in many ways similar to
the projected HMD. This type of HMD is heavier than most other types because of added
electronic components (which also generate large amounts of heat). The user wearing this
type of HMD may feel discomfort due to the heat and the weight of the HMD (Bolas, 1994).
Single Column LED
head mounted display uses one column of 280 LEDs. A mirror rapidly
oscillates opposite from the LEDs, reflecting the image to the user's eye. The LEDs are updated
720 times per oscillation of the mirror. As the LED column updates for each column of the
virtual screen, the mirror redirects the light to the viewers' eye, one column at a time, to form
the image of the entire virtual screen (Aukstakalnis & Blatner, 1992). Single Column LED
HMDs allow the user to interact with a virtual world and the real world simultaneously. This
type of display can be used to create a virtual screen that seems to float in the real world.
One of the common problems of HMDs is that the cable connecting the HMD and a
computer restricts the mobility of the user. The user can only move as far as the cable
allows. If the cable is not properly managed, the user could trip over it or become entangled
in it. In addition, switching frequently between a virtual world and the real world is tedious
and tiresome.
4.2.2 Binocular Omni-Orientation Monitor (BOOM)
The BOOM is mounted on a jointed mechanical arm with tracking sensors located at the joints.
A counterbalance is used to stabilize the monitor, so that when the user releases the monitor, it
remains in place. To view the virtual environment, the user must take hold of the monitor and
put her face up to it. The computer will generate an appropriate scene based on the position
and orientation of the joints on the mechanical arm (Aukstakalnis & Blatner, 1992).
Some of the problems associated with HMDs can be solved by using a BOOM display. The
user does not have to wear a BOOM display as in the case of an HMD. This means that
crossing the boundary between a virtual world and the real world is simply a matter of
moving your eyes away from the BOOM.
