Texture mapping is the process of displaying a scanned picture on a polygon or formation made of polygons. Texture mapping saves on processing because the digitized image is kept in memory and does not have to be continuously redrawn. Until further development, texture mapping is a complex process, requiring much computer-intensive labor and specialized hardware.
If an update rate is too slow, it creates perceptual lag. If it takes longer than 50 milliseconds to register changes in sensor input, it can create problems with performance. Sensor lag is the time spent reading changes and drawing new images.
Virtual environments must be steady and flexible to be plausible. Human perception needs response times of under 100 milliseconds for real time. Any slower than this and the lag becomes noticeable and distracting.
Within this time, the reality engine must process the entire cycle: retrieve user input, perform calculations, and generate a new image. (Again, it takes longer if the images must be generated for left and right eyes, in the case of stereoscopic views.)
If it takes 100 milliseconds to make one pass through the event loop, then one frame is rendered every 0.1 seconds, or 10 frames per second. Movies are shown at 24 fps; television displays at 30 fps. The difference is between interaction and playback; VR images aren't stored in memory; systems must calculate new images every frame. This is what allows interactive movement of the viewpoint to any location or orientation in the 3-D world.
Factors that affect the immersive quality of a virtual experience
include:
Field of view, which is determined by whatever device is
used to display the program. Liquid crystal displays (LCD) have
proved to be the most useful, because they can be made small
enough to fit in front of the face; the Sony Watchman was the
actual prototype used in development of HMDs.
Human eyes have a 180-degree horizontal field of view. VR display optics can create the effect of wrap-around vision that can vary from 80 to 140 degrees. It's like watching a 19-inch television from four or five inches away, with optics keeping it in focus. The more closely the display can match normal vision the better the sense of presence, or immersion; but the optics required to do this affect the resolution because they must also magnify the display screens.
Resolution: Liquid crystal color displays have 360 x 240 color elements. It takes three (1 red, 1 blue, 1 green) to create a picture element (pixel). This means that the LCD can display 29,000 pixels of color image. A PC with a VGA display has 307,000 pixels of information.
Rendering: Drawing speed is measured in frames per second (fps) or Hertz (Hz). To create a sense of presence, a minimum of 10 to 12 fps is good; less than 10 fps has the simulation moving too slow to engage, more than thirty becomes too intricate for comfortable viewing.
This is also the point in building a virtual world. A simple walk-through environment will be less engaging than something that requires some kind of hands-on involvement. A virtual world that has the user flying through a landscape requires a strong sense of presence, so the world builder may opt to sacrifice resolution for field of view; a more technical VR application requires more resolution.
The creation of an environment requires the immersion of one's senses in a computer-generated world, the perception of being there. The problem isn't whether the virtual world is as real as the physical world, but whether the created world is real enough for one to suspend disbelief for its duration.
The visual space in Virtual Reality has height and width; the world-builders do their best to provide the illusion of depth and volume, and time and motion are essential to its operation. The aesthetic principles that define the four- dimensional field can therefore definitely be employed with it.
Pimentel & Teixeira believe that the aesthetic principles that apply to television and film should be employed for VR: "One way to improve the quality of interaction with computers is to learn Hollywood's techniques of entertainment. Hollywood understands realism and narrative--what it takes to involve the audience and create a compelling experience...Computer people understand interactivity. They know how to use computers to create a form of conversation with the user." (Pimentel & Teixeira, 39)
In structuring a four-dimensional field for VR one must consider
the visual field of the virtual world; how it is similar to film
and television representation but also how it differs.
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