Glossary U-Z

undevelopable surface	(n) A surface of an object that cannot be unfolded or unrolled onto a plane without distortion. Double-curved surfaces, such as spheres, are undevelopable.
unevaluated	(adj.) A description of a model for which the final form is not explicitly represented in the database. An evaluated model is concise (i.e., it takes up smaller amounts of memory), but it is not efficient since portions of the model must be defined “on-the-fly” before the user-requested operations can be processed.
unidirectional dimensioning	(n) A style of dimensioning in which the dimension and note text are oriented to be read from the bottom of the drawing, relative to the drawing format. This is an ANSI approved style of dimensioning.
union (∪)	(n) The Boolean operation that combines the two specified solids. If the two solids intersect, the intersecting geometry is only represented once in the resulting solid.
uniqueness	(adj.) A term used to describe the representation of an object by a computer modeler. The term refers to how close the correspondence is between the representation and the object and whether the representation can in fact represent more than one possible object.
universal product code	(n) See UPC.
UPC	(n) Acronym for universal product code, a coded symbol placed on parts and products. UPC is part of a bar coding system for automatic reading by a laser scanning device. In manufacturing, bar codes are attached to parts, assemblies, and finished products, for tracking the product and for inventory purposes.
upper deviation	(n) A tolerancing term describing the difference between the maximum size limit and the basic size.
upside-down sketching	(n) A technique for improving sketching ability by turning an object upside-down before sketching.
validity	(adj.) A term used to describe the representation of an object by a computer modeler. The term refers to whether the representation actually represents a form that could exist in the real world.
valves	(n) Mechanical devices used to control the flow of liquids and gases through piping systems. The four major functions of valves are to start and stop flow, regulate flow, prevent backflow, and relieve pressure. Valves can either be manual or computer controlled and can be set to respond automatically to conditions in the pipe.
vanishing point	(n) An imaginary point in a perspective drawing or sketch, often on the horizon line, where all projection lines of one dimension of the object converge.
vector value	(n) A quantitative data type that expresses both magnitude and direction.
vertex	(n) The coincidental termination of two or more edges, defined by a point in space. This point indicates a transition from one edge to another and is often the juncture of two or more faces (surfaces).
vertical plane	(n) A plane parallel to the profile plane of projection.
videodisk	(n) An optical storage medium for analog video information. The disk has the advantages of efficient storage of analog information, high image quality, and almost immediate random access; it is similar in technology to the CD-ROM but larger in diameter.
view camera	(n) In 3-D modeling, a metaphorical camera that records what is on the image plane and then, much like a video monitor, shows the image on the computer screen. The image from the camera is contained in a port on the computer screen.
view volume	(n) A theoretical volume defining the region to be rendered. The minimum and maximum Z depths and the viewing bounds on the screen define the three dimensions of the volume. The volume appears as a rectilinear prism in parallel projection and as a truncated pyramid in perspective projection.
virtual condition	(n) The condition resulting from the worst-case combination of size and geometric tolerance applied to a feature. Virtual condition is used in the design of mating parts and for determining gage element sizes. For an external feature, virtual condition is the MMC size plus the geometric tolerance. For an internal feature, it is the MMC size minus the geometric tolerance.
virtual models	(n) A computer-based model analogous to a real or proposed object. Virtual models are endowed with the qualities of a real object, allowing the models to be used in evaluating a proposed design. Virtual models are useful for quickly performing multiple tests that could be destructive to physical models.
virtual reality (VR)	(n) A generic term used to describe artificial environments in which some or all of the human senses are immersed. The term “presence” is often used to describe the degree to which one feels immersed in the virtual environment. VR can be used in engineering design to allow more complete examination of proposed designs without having to build physical prototypes and place them in their planned environments.
visible line	(n) A line type used to represent features that can be seen in the current view. A visible line represents the boundary between two surfaces (faces) that are not tangent or the limiting element of a curved surface.
visual inspection	(v) The process of evaluating a design visually. Visual analysis is often used by industrial designers and marketing professionals to assess the consumer’s aesthetic reaction to a design. This analysis can also be used by engineers to perform a quick confirmation of geometry.
visualization	(v) The process of mentally understanding visual information. Visualization is used with both physical and virtual models to better understand their form and function. The mental image may be analogous to the object represented or of something different. Graphics and the process of creating graphics are used to help stimulate the visualization of proposed designs.
visual science	(n) The study of the visual and technical applications of graphics. Some of the applications of visual science include printing technologies, communications media, visual design, engineering graphics, and artistic drawing.
volume rendering	(n) A visualization technique used with three independent variables mapped to the three geometric dimensions. Each dependent data value is represented by a 3-D volume unit called a voxel, typically coded with color. Various sectioning techniques are used to reveal data values on the interior of the data space.
voxel	(n) The minimum 3-D unit in a volume rendering; equivalent to the pixel in a 2-D rendering.
VR	(n) See virtual reality.
warped surface	(n) A single- or double-curved transitional surface (e.g., cylindroids, conoids, helicoids, hyperbolic paraboloids). Warped surfaces are often approximated by triangulated surface sections, and may join other surfaces or entities together.
washer	(n) A round piece of material with a hole in the center, used with mechanical fasteners to improve the assembling surface, distribute load, and assist in locking nuts. Washers are specified by giving the inside diameter, outside diameter, thickness, type, and name.
web (rib)	(n) A thin, flat feature of an object that acts as a structural support. Ribs, webs, spokes, lugs, and other thin features are not section lined if a cutting plane passes through their long dimension.
width	(n) One of the three principal dimensions of an object. The width dimension is described in the front and top views of a multiview drawing. The width dimension is often associated with the X axis in a 3-D modeling system.
winged-edge data structure	(n) A common 3-D database structure used by boundary representation (B-rep) modelers. This data structure attempts to strike a balance between conciseness and efficiency by providing select redundancy of edges and vertices.
wireframe	(n) The simplest type of data representation for 3-D models. Wireframe modeling is a natural outgrowth of 2-D CAD in that such models only contain information on edges and vertices. With a wireframe modeler, there is no implicit information on the boundary between inside and outside the model volume. Wireframe can also refer to a rendering technique in which only the edges and vertices are represented in the image.
wiring (cabling) diagram	(n) A diagram or drawing showing how the components in an electronic assembly will be connected. Since wiring diagrams often depict the wiring of all the components tied into a single wiring harness, they are also called cabling diagrams. When the drawing depicts how the components are connected to the cable, it is called an interconnection (or point-to-point) diagram. When there are numerous cable connections, it is called a highway diagram.
working assembly drawing	(n) A drawing that combines the detail drawing with the assembly drawing. For relatively simple assemblies using some standard parts, it is possible to combine the detail drawing with the assembly drawing by using a section view.
working drawings	(n) The complete set of standardized drawings that specify the manufacture and assembly of a design. Depending on the complexity of the design, working drawings may be on more than one sheet and may contain written instructions, called specifications. Working drawings are often synonymous with the “blueprints” of a design.
workplane	(n) Often called a construction plane, a 2-D infinitely large plane that can be oriented anywhere in 3-D space. A workplane usually has an associated local coordinate system designated with unique letters (e.g., U, V, W). Workplanes are used to define 2-D geometry used in the development of 3-D models.
world coordinate system	(n) A fixed coordinate system, also referred to as a global coordinate system, used in CAD to define the geometric properties of elements stored in the database. The world coordinate system typically uses either a 2-D (X,Y) or 3-D (X,Y,Z) Cartesian coordinate system.
worm’s eye view	(n) In a perspective pictorial, a viewpoint looking up at the object. From this viewpoint, the ground line is substantially above the horizon line of the object.
Z-buffer	(n) A combination of computer hardware and software which stores depth (Z) information about a rendered model. A Z-buffer contains specialized memory for managing depth information, thus speeding the rendering process, especially in animated sequences.