Glossary G-H

gamut	(n) The range of colors possible at a single pixel on the computer monitor. The gamut is not the full range of colors perceivable by the eye but is typically quite large. The hardware and software of the computer system determine what that gamut will be.
gear	(n) A toothed wheel device that acts as a mechanical linkage to transmit power and motion between machine parts. Most gears transfer rotary motion from one shaft to another. They change the location and can change both the orientation and speed of the rotary motion. Certain gear types transform rotary motion into linear (reciprocating) motion.
gear train	(n) A mechanism consisting of two or more gears and used to transmit power. Normally, gear trains are used to do one or more of the following: increase speed, decrease speed, or change the direction of motion.
general notes	(n) Text placed in the drawing area, including general information that cannot be effectively or quickly communicated through graphical means.
general oblique	(n) A type of oblique pictorial drawing in which the two dimensions of the frontal surface are drawn parallel to the frontal plane and the third (receding) axis is drawn obliquely at any scale between 50 and 100 percent of the frontal plane dimensions. The receding axis is typically drawn at an angle of between 45 and 60 degrees.
general-purpose section line	(n) A default section line symbol used to indicate the cut surface of a sectional view. This symbol is used to represent cast iron, or an anonymous material if none is defined.
generatrix	(n) A straight line for which the path through space describes ruled surfaces or solids. The path the generatrix follows is called the directrix.
geometric dimension	(n) A dimension that specifies the size and location of a feature, as well as other geometric qualities such as form and orientation. Geometric dimensioning and tolerancing, combined with statistical process control, provide a robust approach to inspection and quality control for manufactured parts.
geometric transformations	(v) Basic operations used to modify existing geometry contained in the CAD database. Examples of transformations include translation and rotation. Most transformations used in CAD systems are executed as matrix operations based on linear algebra theory.
geometry	(n) The mathematical method by which elements in space are described and manipulated. Geometry forms the building blocks of engineering and technical graphics. The term is also used to mean shape or form.
GKS (Graphical Kernal System)	(n) A software program that can generate, display, and transfer computer graphics data in a comparative format.
glyph	(n) A compound mark used in a visualization that cannot be classified by other commonly used marks. Glyphs are usually custom designed to encode multiple elements of data into a single mark. The objective for designing glyphs or any other marks is to tap into the innate perceptual abilities of the viewer.
Gouraud shading	(v) A rendering method that uniformly adjusts the value of a surface color based on the relationship of the light source to normals calculated for each vertex of the model. Gouraud shading is sometimes called smooth shading because the vertex normals allow interpolation of shading values across multiple polygons representing the facets of a curved surface.
graphical analysis	(n) Analytic techniques employing primarily graphics to evaluate a potential design, such as the fit of mating parts or the movement of parts in a mechanism.
graphics	(n) A mode of communication using spatial/geometric representations.
grid	(n) A regular pattern of points or lines used to help locate and orient specific marks or features or to help guide the development of sketches and roughly proportion features.
ground’s eye view	(n) In a perspective pictorial, a viewpoint looking up at the object. From this viewpoint, the horizon line is level with the ground line of the object.
ground line	(n) In a perspective drawing or sketch, the point of the object closest to the observer.
group technology	(n) The process of identifying items with similar design or manufacturing characteristics. Items with similar characteristics are grouped into part families.
guideline	(n) A type of construction line used to guide the lettering on the drawing. The term can also refer to lines used for the placement of other elements in a drawing or sketch.
half section	(n) A section view generated by passing a cutting plane halfway through an object. The result depicts half the view sectioned.
half-space	(n) A mathematically defined boundary between two regions. The term is used in constructive solid geometry (CSG) modelers to define the boundary between the solid and the void (nonsolid). Geometric primitives in CSG modelers are defined as groups of half-spaces.
halftone approximation	(n) A method of simulating varying value_(gray) levels within an image when only one color of ink (usually) black is available. Dots of varying size are printed based on the average value level in the region. Because of the small size of the dots compared with the size of the image, the changes of dot size (and therefore ink density) give the impression of value changes when viewed at a distance. Halftones from full-color or gray-scale images can be created both electronically or photographically.
hardware	(n) A term used to define physical computer equipment. Examples of hardware include the monitor (CRT), keyboard, hard disk, and CPU.
height	(n) One of the three principal dimensions of an object. The height dimension is described in the right side and front views of a multiview drawing. The height dimension is often associated with the Y axis in a 3-D modeling system.
helix	(n) A 3-D curve characterized by a constant rate of curvature about two dimensions and a constant linear translation in the third. Threads on screws and bolts are helical and are classified as being either right- or left-handed.
hidden line	(n) A line used to represent a feature that cannot be seen in the current view. Like a visible line, a hidden line represents either the boundary between two surfaces (faces) that are not tangent, or the limiting element of a curved surface. A specific linestyle is defined by ANSI for hidden lines.
hidden surface removal	(v) The rendering process of removing the elements of a model not visible from a particular viewpoint. The removal is accomplished by calculating the relationship of edges and surfaces along the depth axis.
hierarchy	(n) An ordered set of elements in which each element belongs to a specific level. An element at each level can be a parent to elements below it on the hierarchy, or a child to elements above it, or both. Hierarchies are used to describe the organization of files in a computer system, or geometric primitives in a CAD model.
highway diagram	(n) See wiring diagram.
histogram	(n) A visualization technique used to summarize data by reporting the number of data points that fall within a certain range of values. Histograms are often represented as bar graphs. Because histograms provide only a summary, they depict the original information only indirectly.
hole basis	(n) A tolerancing measure used to describe a system of fits in which the minimum hole size is the basic size.
hole loop	(n) A close group of edges on the interior of an object, defining a penetration that goes part or all the way through. The number of hole loops is one of the variables in the Euler–Poincaré formula used to validate the topology of a model.
HOOPS (Hierarchical Object-Oriented Picture System)	(n) A software program that can generate, display, and transfer computer graphics data in a compatible format.
horizon line	(n) In a perspective sketch, a horizontal line marking the location where all projection lines from the observer converge.
horizontal line	(n) A line seen in its true size in the horizontal plane.
horizontal plane	(n) A principal orthographic plane of projection, used to define both the top and bottom orthographic views.
HSV color model	(n) A model based on the perceptual components of color, that is, (H)ue, (S)aturation, and (V)alue (lightness), modeled as a hexacone. Hue is laid out in a radial pattern around the hexacone, saturation ranges linearly from full saturation at the perimeter to white at the center, and value runs from the base of the hexacone (white) to the point (black).
hue	(n) The dominant spectral wavelength of a perceived color. Hue and color are often confused because the name given to the hue is often synonymous with the name of the color.
human’s eye view	(n) In a perspective pictorial, a viewpoint looking slightly down at the object. From this viewpoint, the ground line is equivalent to six feet below the horizon line of the object.
human factors analysis	(v) A process for evaluating a design to determine if the product serves the physical, emotional (aesthetic), quality, mental, and safety needs of the consumer. Specialists in human factors or ergonomics are often employed to conduct this evaluation.
hybrid modeler	(n) A 3-D modeling system that combines the operations and database structure of more than one of the commonly defined modeling systems. Used with more powerful computing systems, these modelers combine the advantages of more than one system. An example is the combination of CSG and surface modeling technology.
hyperbola	(n) A single-curved surface primitive, created when a plane intersects a right circular cone at an angle with the axis that is smaller than that made by the elements.
hypermedia	(n) An interactive, computer-based information system, created with authoring tools, which allows flexible, nonlinear access. Information is linked both through elements selected within the body of the information and through sophisticated search engines.