Glossary I

ideation	(n) A structured approach to thinking for the purpose of solving a problem, often employing graphics. Ideation is the conceptual phase of the design process. Feasibility studies are often performed to define the problem, identify important factors that limit the scope of the design, evaluate anticipated difficulties, and consider the consequences of the design.
ideation drawings/sketches	(n) A type of freehand sketch or drawing used early in the design process to explore design ideas quickly. These sketches are usually rough and incomplete, typically not following many of the conventions used for more finished drawings.
IGES	(n) Acronym for initial graphics exchange specification, an indirect data exchange standard used largely in the United States to exchange CAD information between disparate systems. Originally developed by the U.S. government and major defense contractors, it is used mainly on workstation, minicomputer, and mainframe-based CAD systems.
image plane	(n) An imaginary plane on which an object is projected. The graphic representation of an object on a computer screen or paper is an example of a projection as it would appear on an image plane.
inclined edge/line	(n) An edge of a face that is parallel to a plane of projection but inclined to the adjacent orthogonal planes. The edge appears as an inclined, true-length line in one of the principal views and is foreshortened in the two adjacent views.
inclined face	(n) A planar face (surface) of an object that has been rotated about one axis from one of the principal image planes. An inclined face will appear foreshortened in two of the principal views and as an edge in the third.
independent variable	(n) A variable for which the values are controlled by the experimenter to create a response in the model as measured by the dependent variable. Every independent variable value is paired with one or more dependent variables and represents the experimental manipulation of the model.
indirect data exchange	(n) A method of translating data from one CAD system to another through an intermediate, neutral data format. Examples of intermediate data formats include IGES and DXF.
industrial engineering	(n) A field of engineering concerned with the analysis and design of systems for organizing the basic production resources such as personnel, information, materials, and equipment. Industrial engineers use mathematics, the physical and engineering sciences, and the management and behavioral sciences.
infinite light source	(n) A light source located at a theoretically infinite point in space. The sun is analogous to an infinite light source. In rendering, the user specifies an orientation for the light rays, all of which are parallel to each other.
initial graphics exchange specification	(n) See IGES.
input device	(n) Computer hardware used by the operator to input information into a software program. Examples are keyboard, mouse, scanner, etc.
instances	(n) Cloned copies of geometry already existing in a database. Typically, an instance is linked directly to the geometric and topological information of its parent but contains unique information pertaining to its location, orientation, and scale in the model/drawing. Some systems refer to instances as symbols.
integrated circuit	(n) An electronic component made up of a large number of diodes, transistors, and resisters and integrated onto a single semiconductor substrate such as silicon. An example of an integrated circuit is a central processing unit (CPU) in a computer.
intensity depth cueing	(n) A rendering technique which calculates the Z-depths of the edges in a model and sets their brightness (intensity) relative to their depths. This technique taps the aerial perceptual depth cue and has the effect of making the model fade as it goes back in depth.
interconnection diagram	(n) See wiring diagram.
interference fit	(n) A fit in which two toleranced mating parts will always interfere when assembled because the “male” part is larger than the “female” part. The resulting difference in sizes, also called the allowance, means that force is required to assemble the part. An interference fit fixes or anchors the two parts as if they were one.
International System of Units	(n) See SI.
international tolerance grade	(n) A group of tolerances that vary depending on basic size but have the same level of accuracy with a given grade. The smaller the grade number, the smaller the tolerance zone.
intersecting lines	(n) Lines that share one or more common points in space. Lines that share all their points in common, or lines for which one could be considered a subset of the other, are called coincident.
intersection	(n) The Boolean operation in which only the intersecting geometry of two solids remains.
interval scale	(n) A data scale that preserves the units used but does not have a natural zero point. Interval scales often result from the difference between two values using the same scale.
involute	(n) A curve defined as the spiral trace of a point on a flexible line unwinding from around a line, circle, or polygon. The contacting surfaces between gear teeth are designed as involutes.
isometric drawing	(n) A pictorial representation of an object rotated 45 degrees, tilted 36 degrees 16 minutes, then drawn full scale. An isometric drawing differs from an isometric projection in that all three dimensions are drawn at full scale rather than foreshortening to the true projection.
isometric ellipses	(n) A special type of ellipse used to represent holes and ends of cylinders in isometric drawings. In an isometric drawing, circular features are often not viewed normally, foreshortening them and making them appear as ellipses.
isometric grid	(n) A network of evenly spaced lines drawn at 30, 90, and 120 degrees. Paper preprinted with this grid is used to sketch isometric drawings.
isometric line/plane	(n) A line or plane that is parallel to one of the principal isometric axes or to two adjacent isometric axes, respectively. Isometric lines and planes are typically the simplest elements to represent in an isometric drawing.
isometric projection	(n) An axonometric projection in which three of the axes are measured on the same scale and are at the same angle relative to each other. An isometric drawing is less pleasing to the eye than other types of axonometric projections, but it is the most common since it is the easiest to draw.
isosurfaces	(n) A surface in 3-D space that defines constant values of a dependent variable. Isosurfaces are the logical extension of contour lines (isolines), which map constant values in 2-D space. Every point on an isosurface identifies the location where three independent variable values result in the dependent variable value of interest. Like isolines, multiple isosurfaces can be used to map different dependent variable values.
italic	(adj.) A style of text in which vertical elements of letters are slanted forward. This technique is used to make words or letters visually stand out from the rest of the text.