17-01-2014, 02:07 PM
Data Glove and Digitizers
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INTRODUCTION
Fig. shows a data glove that can be used to grasp a “virtual” object. The glove is constructed with a series of sensors that detect hand and finger motions. Electromagnetic coupling between transmitting antennas and receiving antennas is used to provide information about the position and orientation of the hand.
The transmitting and receiving antennas can each be structured as a set of three mutually perpendicular coils, forming a three-dimensional Cartesian co-ordinate system. Input from the glove can be used to position or manipulate objects in a virtual scene. A two-dimensional projection of the scene can be viewed on a video monitor, or a three dimensional projection of the scene can be viewed with headset.
Digitizers
A common device for drawing, painting or interactively selecting co-ordinate positions on an object is digitizer. These devices can be used to input co-ordinate values in either a two-dimensional or a three dimensional space.
One type of digitizer is the graphics tablet and it is also referred to as a data tablet which is used to input two-dimensional co-ordinates by activating a hand cursor or stylus at selected positions on a flat surface.
A hand cursor contains cross hairs for sighting positions, while a stylus is a pencil-shaped device that is pointed at positions on the tablet.
Working principles:
Two electron guns are used in a DVST.One, the primary gun, is used to store the picture pattern; the second, the flood gun, maintain the picture display. Just behind the storage mesh is a second grid called the collector. The function of the collector is to smooth out the flow of flood electrons. Since a large number of electrons are produced at high velocity by the flood gun, the collector grid, which is also negatively charged reduces, the acceleration on these electrons and the resulting low velocity flood pass through the collector and get attracted by the positively charged portions of the storage mesh (Since the electrons are negatively charged), but are repelled by the other portions of the mesh which are negatively charged (Note that the pattern of positive charges residing on the storage mesh actually defines the picture to be displayed).
Thus, the electrons attracted by the positive charges pass through the mesh, travel on to the phosphor coated screen and display the picture. Since the collector has slowed the electrons down, they may not be able to produce sharp and bright images.
Graphics Monitor &Workstation
Most graphics monitors today operate as raster scan displays, and here we surveya few of the many graphics hardware configurations available. Graphics systems range from small general-purpose computer systems with graphics capabilities (Fig. 1) to sophisticated full color systems that are designed specifically for graphics applications (Fig. 2).
A typical screen resolution for personal computer systems as shown in fig-1, although screen resolution and other system capabilities vary depending on the size and cost of the system. Diagonal screen dimensions for general-purpose personal computer systems can range from 12 to 21 inches, and allowable color selections range from 16 to over 32,000. For workstations specifically designed for graphics applications, such as the systems shown in Fig. 2, typical screen resolution is 1280 by 1024, with a screen diagonal of 16 inches or more. Graphics workstations can be configured with from 8 to 24 bits per pixel (full-color systems), with higher screen resolutions, faster processors, and other options available in high-end systems
Liquid Crystal Display (LCD)
A liquid crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals. Liquid crystals do not emit light directly. LCD panels produce no light of their own; they require external light to produce a visible image.
LCD displays utilize two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light.
Monochrome LCD images usually appear as blue or dark gray images on top of a grayish-white background. Color LCD displays use two basic techniques for producing color: Passive matrix is the less expensive of the two technologies (e.g. calculators, wristwatches) and Passive-matrix displays are usually not backlit. The other technology, called thin film transistor (TFT) or active-matrix, produces color images that are as sharp as traditional CRT displays, but the technology is expensive and active-matrix displays almost always are backlit.
Physics behind LED
The LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.
The wavelength of the light emitted, and thus its color depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radioactive transition, which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible, or near-ultraviolet light.
LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have enabled making devices with ever-shorter wavelengths, emitting light in a variety of colors. LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.