Glossary

There are a number of specialized terms in the Volumetric display industry and so I figure I will need a glossary to help me out. This entry will serve as that Glossary. I'll update it whenever I come across a new word.

• Direct Volume Display Devices (DVDDs) - Essentially, another name for a Volumetric Display: a graphical display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. (from Wikipedia.)
  
• Emissive Volume Displays - A Volumetric Display that works by suspending active elements in a 3-D volume space. Normally in the "off" state, these elements are either dark or transparent and become opaque or luminous when put into the "on" state. These elements could be LCD panels as implemented by Lightspace technologies or a florescent agent lit up by fiber optics like the prototype built at the Dallas campus of the University of Texas.
  
• Laser Plasma Displays - A relatevely new type of Volumetric Display that works by focusing a pulsed infrared laser at a point in the air to generate a small glowing ball of plasma. The National Institute of Advanced Industrial Science and Technology (AIST) recently reported success with their version of the system. As the laser is able to produce plasma gas out of regular air, safety concerns would be paramount since the laser could severely burn your hand if you passed it through the display volume.
• Multiplaner Display Systems - Essentially, another name for a Volumetric Display: a graphical display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects. (from Wikipedia.)
• Swept-Volume Displays - The most popular type of Volumetric Display which works by sweeping the volume with a 2-D surface while a laser, a series of LEDs, a projection CRT or other device displays an image on the surface. Most swept plane displays are implemented by rotating a flat translucent surface like that demonstrated by the Holoverse Group. Less popular swept plane displays employ complex shapes like the helical assembly described by Laserfx.com. Swept plane displays require elaborate moving parts and therefore are susceptible to vibration, wobbling and other mechanical flaws.
  
• Varifocal Mirror Displays -A Volumetric Display that shows 3-D images by using a variable focus mirror to focus 2-D images at different depth planes. Normally, the mirror is vibrated rapidly in order to swept its focus across the volume. However, to show a display with high quality, the mirror must be capable of vibrating at very high frequencies. Varifocal mirror displays are one of the oldest types of volumetric displays and they were built as early as the 1960s. One example of the varifocal mirror display is the SpaceGraph system built by BBN in Cambridge, MA.
• Volumetric Display -A volumetric display device is a graphical display device that forms a visual representation of an object in three physical dimensions, as opposed to the planar image of traditional screens that simulate depth through a number of different visual effects (perspective, shading, etc.) (from Wikipedia.) What distinguishes volumeric displays from other types of 3-D displays (such as stereoscopic or holographic displays) is that they create real 3-D images that appear to float in midair, can be viewed from a wide variety of angles and does not require the use of special glasses (like most stereoscopic dislays). Holographic displays work by projecting interference patterns on the retina of the eye: the viewer is seeing a virtual image of an object instead of a real image. Volumeric displays also do not induce the eystrain many different types of stereoscopic displays generate.
  
• voxel - (VOlume piXEL) A three-dimensional pixel. In other words, the smallest element displayed in a three -dimensional image.
• Voxel Density - I'm not quite sure what this is yet. I believe it is the 3-D equivalent to pixel density. In other words, the grayscale intensity of a voxel expressed as a number in the range 0..1. (This term needs more research)
  
• Voxel Intensity - The relative brightness of a Voxel. There is a direct, linear relationship between voxel intensity and opacity. In other words, by default, the higher a voxel's intensity value, the more opaque (less transparent) that voxel is when rendered. (From the University of Iowa's Advanced Technologies website.) (Definition link)
• Voxelization - the process of adding depth to an image using a set of cross-sectional images known as a volumetric dataset. (From Webopedia)
  
• Voxel Opacity - A measure of the opacity of a voxel. Any voxel has the capability of obscuring the view of any other voxel. To get around this, voxels are given an opacity value through an opacity transformation function. There is a direct, linear relationship between voxel intensity and opacity. In other words, by default, the higher a voxel's intensity value, the more opaque (less transparent) that voxel is when rendered. (From the University of Iowa's Advanced Technologies website.) (Definition link)
  
• Voxel Processing - A means of visualizing 3-dimensional shapes and structures implied by a series of cross-sectional images. (From the University of Iowa's Advanced Technologies website.) (Definition link).
  

(Updated 4/7/06)