Environmental Engineering Reference
In-Depth Information
mainframe computer terminal or a personal computer (PC) connected to a network.
Workstations had offered higher performance than personal computers, especially with
respect to CPU and graphics, memory capacity and multitasking capability. They are
optimized for the visualization and manipulation of different types of complex data such as
3D mechanical design, engineering simulation animation and rendering of images, and
mathematical plots. Workstations are the first segment of the computer market to present
advanced accessories and collaboration tools. Presently, the workstation market is highly
commoditized and is dominated by large PC vendors, such as Dell and HP, selling
Microsoft Windows/Linux running on Intel Xeon/AMD Opteron. Alternative UNIX based
platforms are provided by Apple Inc., Sun Microsystems, and Silicon Graphics International
(SGI) (http://en.wikipedia.org/wiki/Workstation).
4.2 Sensory displays
Sensory displays are used to display the simulated virtual worlds to the user. The most
common sensory displays are the computer visual display unit, the head-mounted display
(HMD) for 3D visual and headphones for 3D audio.
4.2.1 Head mounted displays
Head mounted displays place a screen in front of each of the viewer's eyes at all times. The
view, the segment of the virtual environment generated and displayed, is controlled by
orientation sensors mounted on the “helmet”. Head movement is recognized by the
computer, and a new perspective of the scene is generated. In most cases, a set of optical
lens and mirrors are used to enlarge the view to fill the field of view and to direct the scene
to the eyes (Lane, 1993). Four types of Head Mounted Displays (HMDs) are: (a) Liquid
Crystal Display (LCD) head mounted display; (b) Projected head mounted display; (c) Small
CRT head mounted display; and (d) Single Column LED head mounted display.
LCD head mounted display uses LCD technology to display a scene. When a liquid crystal
pixel is activated, it blocks the passage of light through it. Thousands of these pixels are
arranged in a two dimensional matrix for each display. Since liquid crystals block the
passage of light, to display a scene a light must be shone from behind the LCD matrix
toward the eye to provide brightness for the scene (Aukstakalnis & Blatner, 1992). LCD head
mounted display is lighter than most HMDs. As with most HMDs, it does provide an
immersive effect, but the resolution and the contrast are low. The problem associated with
low resolution is inability to identify objects and inability to locate the exact position of
objects. Since the crystals are polarized to control the color of a pixel, the actual polarizing of
the crystal creates a small delay while forming the image on the screen. Such a delay may
cause the viewer to misjudge the position of objects (Bolas, 1994).
Projected head mounted display uses fiber optic cables to transmit a scene to the screen. The
screen is similar to a cathode ray tube (CRT) except the phosphor is illuminated by the light
transmitted through fiber optic cables. Ideally, each fiber would control one pixel. But due
to the limitation in cost and manufacturing, each fiber controls a honeycomb section of
pixels (Lane, 1993). Projected head mounted display provides better resolution and contrast
than LCD displays. This HMD is also light weight. Higher resolution and contrast means
that the viewer is able to see an image with greater detail. The downside of this type of
HMD is that it is expensive and difficult to manufacture (Bolas, 1994).
