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Glossary A thru D
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Glossary Terms A thru D
absolute coordinates  (n) Coordinates associated with an origin that never changes location and thus gives a stable method of locating geometry in space. The absolute coordinate system is also called the world or global coordinate system.
absolute scale  (n) A data scale that has both a defined zero point and units. The Kelvin temperature scale is an example of an absolute scale.
actual size  (n) A tolerancing measure used to describe the size of a finished part after machining.
additive  (adj. or v) A process or state whereby elements combine together, such as two primitive shapes combining to form a larger, more complex one. Additive is the opposite of subtractive.
additive primaries  (n) The three primary colors: red, green, and blue. Color systems use these primaries in differing amounts, working on the principle of adding spectral wavelengths to the light energy to create new colors. This system is used in lighting and computer display graphics. The complementary colors are the subtractive primaries: cyan, magenta, and yellow.
adjacent areas  (n) Surfaces that are separated on a multiview drawing by lines that represent a change of planes. No two adjacent areas can lie in the same plane.
adjacent view  (n) Orthographic views that are aligned to each other, allowing dimensional information to be shared. Examples are the front and top views or the front and right side views.
aerial perspective  (n) A perceptual cue where objects farther away appear bluer and hazier. The cue is based on the effect of particles in the atmosphere blocking the passage of light.
aerospace engineering  (n) A field of engineering concerned with the design and operation of aircraft, missiles, and space vehicles.
aesthetics  (n) The artistic qualities or aspects that elicit an emotional response to an object.
agricultural engineering  (n) A field of engineering concerned with production agriculture and its natural resource base and the processing and chemistry of biological materials for food and industrial products.
aligned dimensions  (n) A style of dimensioning in which text is placed parallel to the dimension line, with vertical dimensions read from the right of the drawing sheet. The aligned method of dimensioning is not approved by the current ANSI standards but may be seen on older drawings.
aligned section  (n) A section view created by bending the cutting plane line to pass through an angled feature. The resulting section does not show the section in true projection, yet it gives the clearest possible representation of the features.
allowance  (n) A tolerancing measure used to describe the minimum clearance or maximum interference between parts. Allowance is the tightest fit between two mating parts.
alphabet of lines  (n) The standard linestyles established by ANSI to be used for technical drawing. The standards specify both the thickness and the design (i.e., dashed, solid, etc.) of the lines.
alternate four-center ellipse method  (n) A method of creating an approximate ellipse. The method is used for cavalier oblique drawings.
ambient light source  (n) A light source defined by its lack of orientation or location. Fluorescent lighting in an office is an example of ambient lighting. In renderings, an ambient light source is sometimes used as a default light source to give a baseline level of lighting to the model.
analogous  (adj.) A concept meaning similar or comparable in some respects. The concept is used to describe the extent to which a graphic representation compares with a real object.
analytic geometry  (n) The analysis of geometric structures and properties, principally using algebraic operations and position coordinates. The term also refers to a particular geometric method for describing 3-D solid models.
angle  (n) The relative orientation of two linear elements with respect to each other. The angle is usually measured relative to the point of intersection or termination of the two lines.
angularity  (n) An orientation control for geometric dimensioning and tolerancing. Angularity is a condition of a surface, center plane, or axis at an angle other than a right angle to a datum plane or datum axis.
apparent motion  (n) The sense of motion induced by rapidly displaying a series of images of an object to make the object appear to change location or shape. Animation techniques take advantage of this perceptual effect.
archiving  (v) A term used to describe the storing and retrieval process for engineering documentation. Although originally involving paper documents, the term increasingly refers to the storage of computer-generated information on magnetic or optical media.
area rendering  (n) A data visualization technique in which the pixels in a 2-D area are each assigned a value. A color lookup table maps a specific color to each data value to create a rendered region.
array  (n,v) Either the process of or resulting geometry of a single feature being duplicated in a regular fashion in a model. An array is procedural, in that instructions are given as to how a feature(s) is to be duplicated rather than having the user define the final location of each duplicate. Arrays are defined as being either linear or radial, depending on how the duplication is defined. Typically, the operator will indicate the direction (in one or two dimensions) of the duplication, spacing between each duplicate feature, and how many duplicates to create.
arrow plot  (n) A visualization technique in which the dependent variable is a vector rather than a scalar and is represented by line or arrow marks. Because there are typically a large number of arrow marks in a small region, pattern (texture) perception can be used to evaluate trends in the data.
artistic drawing  (n) A type of drawing used to express aesthetic, philosophical, and abstract ideas. These types of drawings are not intended to communicate clear, concise information pertaining to a design.
artwork drawing  (n) See fabrication drawing.
assembly drawing  (n) A drawing showing how each part of a design is put together. An assembly drawing normally consists of all the parts drawn in their operating positions and a parts list or bill of materials.
assembly section  (n) A section view of multiple parts in an assembly. Differing section line designs differentiate between different materials, or between similar materials belonging to different parts.
authoring  (v) The process of using computer programming tools to assemble different media into an interactive presentation. automation (n) The use of machinery in place of human labor.
autorouting  (v) A specialized software process that suggests routing connections between components on a circuit board. Autorouting is usually part of a suite of CAD electronics software functions that also include automated component placement, programming of CNC board drilling, and component insertion equipment.
auxiliary section  (n) A section view derived from an auxiliary view. The term distinguishes from section views derived from standard orthographic views.
auxiliary view  (n) A view derived from any image plane other than the frontal, horizontal, or profile planes. Auxiliary views are usually termed primary or secondary, depending on whether or not they are perpendicular to one of the above-mentioned primary projection planes. Primary auxiliary views are termed depth, height, or width auxiliaries, depending on the dimension transferred from the measuring view.
axis  (n) The line or vector representing a center of rotation, such as the longitudinal center line that passes through a screw thread cylinder. Also, a vector indicating a dimension in model space or in a visualization such as a graph.
axonometric axes  (n) The axes used to define the orientation of the primary dimensions in an axonometric pictorial projection. The relative angle of the axes to each other determines the type of axonometric projection.
axonometric projection  (n) A parallel projection technique used to create pictorial drawings of objects by rotating the object on an axis relative to a projection plane.
automation  (n) The use of machinery in place of human labor.
B-spline curve  (n) A parametrically defined freeform curve that approximates a curve to a set of control points and provides for local control. Multiple 2-D curves are often combined to create 3-D surface patches.
backface culling  (n) In rendering, a preprocessing step that removes all faces of the model that will be completely hidden from view.
bar graph  (n) A graph (usually 2-D) in which one dimension represents the independent variable and the other represents the dependent variable. The magnitude of the dependent variable is represented by a line or area of uniform width (a bar).
basic dimension  (n) A tolerancing measure used to describe the theoretically exact size of a feature.
basic size  (n) A tolerancing measure used to describe the theoretical size used as a starting point for the application of tolerances.
bearing  (n) A mechanical device designed to transfer radial or axial loads from a shaft while minimizing energy loss due to friction from the rotating shaft. Bearings are usually divided into two general categories: plain and rolling contact.
Bezier curve  (n) A special case of the B-spline curve. Unlike a standard B-spline curve, the Bezier does not provide for local control, meaning that changing one control point affects the entire curve.
bicubic surface patch  (n) A 3-D freeform surface bounded by a set of curves described by third degree (cubic) functions. The bounding curves, often B-spline or Bezier curves, and their associated control points are used to manipulate the shape of the surface.
bill of materials  (n) A listing of parts or materials used in an assembled object. The listing is usually included as part of the working drawing of the full assembly.
binary tree  (n) A hierarchical, logical structure used to organize related elements. Each node on the tree is linked to exactly two leaves on the next level down. Binary trees are used to describe the relationship of geometric elements in a CSG solid modeler.
bird’s eye view  (n) In a perspective pictorial, a viewpoint looking down from above the object. From this viewpoint, the ground line is below the horizon line of the object.
blind hole  (n) A hole that does not go completely through the material. Blind holes can be created by any cutting device (such as a twist drill bit) that is capable of plunging into the material.
block diagram  (n) A relatively simple diagram that quickly identifies the relationships between systems, groups, people, or other physical or abstract entities. (See also flow diagrams.)
boldface  (adj.) A style of text in which the lines that make up the letters are thicker than normal. This technique is used to make words or letters stand out visually from the rest of the text.
bolt  (n) A mechanical fastening device with a head on one end of an externally threaded shaft. A nut is placed on the threaded shaft and rotated to clamp the material between the head and nut.
bonding  (v) A process in which a material (usually, a hardening liquid) is added to an assembly to hold parts together. Bonding is a permanent fastening method, using processes such as welding, soldering, brazing, and gluing.
Boolean operations  (v) Local operations used to define the relationship between two geometric objects. Boolean operations between new and existing geometry are used extensively to modify solid models in 3-D modeling software.
bottom view  (n) A principal view of an object, created by rotating the object 90 degrees about the horizontal axis below the front view. This view is not typically included in a standard multiview drawing.
boundary representation (B-rep)  (n) A popular method of representing solid models. This database structure describes the geometric and topological elements of the surface of the model. Unlike wireframe modeling, a B-rep explicitly defines the surface of the model. Unlike CSG modeling, a B-rep does not explicitly define the interior volume of the object.
bounding box  (n) An imaginary box representing the maximum dimensions of the object being drawn. Sketches of objects often begin with this box, and it is used to define the boundaries and guide the placement of individual features.
brainstorming  (v) A process used to identify as many solutions to a design problem as possible by freely suggesting ideas without criticism or discussion of feasibility. A brainstorming session will normally have a moderator and a recorder.
break lines  (n) Freehand lines used to show where an object is broken to reveal interior features of a part. Such lines can also be used to show where a portion of a line or object has been left out for clarity or because of space limitations.
broken-out section  (n) A section view used to reveal interior features of a part by breaking away a portion of the object. A broken-out section is often used instead of a half or full section view when the feature of interest is not symmetrical with the overall object. The result is a more efficient drawing. Unlike most other section views, a cutting plane line is not defined in an adjacent view.
bump mapping  (n) A rendering technique used to add surface detail to a model. Bump mapping perturbs the normals used in shading the surface polygons in such a way as to give the impression of a regularly undulating surface (i.e., texture). A golf ball could be represented as a shaded sphere, with the dimples created through bump mapping.
cabinet oblique  (n) Atype 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 half the scale of the frontal plane. The receding axis is typically drawn at an angle of between 45 and 60 degrees.
cabling diagram  (n) See wiring diagram.
CAD  (v or n) Acronym for computer-aided drafting, computer-aided design, or computeraided design/drafting. The usage depends on the context in the design process and on whether the acronym refers to the physical computer system or the activity of using such a system to support technical and engineering graphics.
callouts  (n) See line balloon.
cam  (n) Amechanical device used to transform rotary motion into reciprocating motion, using a rolling or sliding contact with another part called a cam follower. Radial cams move the follower perpendicular to the shaft; cylindrical cams move the follower parallel to the shaft. The shape of the contact surface determines the motion of the follower.
CAM  (n) Acronym for computer-aided manufacturing, which is the use of computers to control the production process. Examples are robots for assembly and numerically controlled machine tools. CAM is often combined with CAD to describe the integration of design and manufacturing through the use of a common computer database.
cam follower  (n) Amechanical device in which one end follows a linear, reciprocating path as the other end traces the surface of a rotating cam. Followers are often spring loaded to guarantee a good contact with the surface of the cam.
cap screw  (n) Amechanical threaded fastener with a head on one end, used to screw into a mating part. Differing from a bolt, a cap screw has a longer thread length and does not use a nut.
CAPP  (n) Acronym for computer-aided process planning, a technique that uses computers to assist in the planning process. CAPP is an expert computer system that can be used to determine the optimal sequence of operations for a part and can then generate the optimal process and routing sheets necessary to make the part.
Cartesian coordinate system  (n) Common coordinate system used in mathematics and graphics to locate the position of geometry in space. First introduced in 1637 by Rene Descartes (1596–1650), the system is typically used to locate points in 2-D (X,Y) or 3-D (X,Y,Z) space by assigning values to the points based on the mutually perpendicular (orthogonal) axes.
cavalier oblique  (n) A type of 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 to the frontal plane and at the same scale. The receding axis is typically drawn at an angle of between 45 and 60 degrees.
CD-ROM  (n) Acronym for compact disk-read only memory, a mass storage device that uses optical technology to store large amounts of information on a small reflective platter. Information is written to the disk only once, at which point the disk is unchangeable. CDROMs are used for archiving audio, graphic, and textual information, and for publishing and distributing software, graphic images, multimedia materials, etc.
center lines  (n) A type of linestyle used to represent symmetry and paths of motion and to mark the centers of circles and the axes of symmetrical parts, such as cylinders and bolts. Unlike visible and hidden lines, center lines do not represent geometry directly.
central view  (n) The view from which related views are aligned in an orthographic drawing. Distances and features are projected or measured from the central view to create the adjacent views.
ceramics  (n) Materials, usually with crystal structures, created from compounds of metallic and nonmetallic elements. Ceramics can withstand high temperatures and resist wear. Some ceramics, such as glass, are not crystalline in structure.
chamfer  (n or v) A beveled corner used on the opening of a hole and the end of a cylindrical part to eliminate sharp corners. Chamfers facilitate the assembly of parts and are specified by giving a linear and angular dimension. When used as a verb, the term refers to the process of creating a chamfer on an object.
check print  (n) A type of hard-copy output used to check the accuracy and format of a technical drawing. The check print is a lowquality, high-speed method of troubleshooting the final print or plot.
chemical engineering  (n) A field of engineering that includes all phases of technical activities in which a knowledge of chemistry, along with other basic sciences, is used to solve problems related to energy, health, the environment, food, clothing, shelter, and materials.
CIM  (n) Acronym for computer-integrated manufacturing, a system for linking manufacturing operations into a single integrated computer system. CIM differs from CAD/CAM primarily in its integration of business functions, such as accounting, marketing, and personnel, into a common computer database shared by all components of the business.
circle  (n) A closed, planar curve that, at all points, is an equal distance (the radius) from a point designated as the center. A circular arc is an open, planar curve equidistant from a center. The arc will subtend an angle of less than 360 degrees. Acircle is sometimes described as a 360-degree arc.
circuit side  (n) The side of a printed circuit board on which a majority of the circuit connections for components are made. The opposite side of the board is called the component side.
circularity (roundness)  (n) A form control for geometric dimensioning and tolerancing. For a cylinder or cone, circularity means that all points on a surface intersected by a plane passing perpendicular to a common axis are equidistant to that axis. For a sphere, all points on a surface intersected by a plane passing through the center are equidistant to that center.
civil engineering  (n) A field of engineering involved with planning, design, construction, operation, and maintenance of transportation, environmental, and construction systems. Along with military engineering, this field is often considered the first true engineering field.
civil piping  (n) The piping used to transport water and waste at the municipal level.
clash  (v) A condition in which two parts of a mechanism partially overlap in space, causing interference. Kinematic analysis using the Boolean intersection operation is often used to evaluate clashes in computer models of the mechanism.
clearance fit  (n) A tolerancing measure used to describe a fit in which two mating parts always leave a space when assembled. The resulting space is called an allowance or a clearance and is usually specified in the assembly drawings.
clip  (v) The rendering process of removing portions of lines or surfaces that reside outside the view volume. Clipping refers to removing the portion of the model that resides outside the horizontal and vertical bounds of the viewing area and outside the specified near and far depth (Z) bounds.
clock speed  (n) The rate at which the central processing unit (CPU) of the computer performs functions. The clock speed is measured in megahertz (MHz). The higher the clock speed, the more powerful the CPU.
closed loop  (n) The condition required for a group of edges to form a face (surface) on an object. The edges must be connected end to end, forming a continuous path around the perimeter of the face.
CNC  (n) Acronym for computer numeric control, which describes a form of programmable automation of a machine tool using a computer in the controller unit. In a computer controlled manufacturing center, the individual machines would use CNC programs, either sent from a main computer or programmed locally.
color  (n) The perceptual quality of a surface that results from the combined response to lightness, hue, and value. Hue is often confused with color since the names of hues (e.g., red, purple, yellow, etc.) are used as the primary classification terms for color.
color lookup table  (n) A modular database that allows colors to be mapped to specific data values in a visualization. The color lookup table can be associated with a single rendered image or be used as a standard table in a library. Color lookup tables are often referred to as palettes.
command history  (n) A listing of commands entered into the CAD system by the user, along with the values of the specified parameters. Command histories can be used as a “script” to replay sequences of commands or track down input errors.
composites  (n) The combination of two or more materials, one a reinforcing element and the other a resin binder or matrix. A common composite is fiberglass, which is made of glass fibers and a resin. The more advanced reinforcing elements include carbon/graphite, boron, and Kevlar (aramid), which are stiff, strong, and lightweight.
computer animation and simulation  (n) Simulation is the precise modeling of complex situations that involve a time element; animation is the imprecise modeling of complex situations over time. An animation will replicate a real situation by approximate means; a simulation will replicate a real situation by accurate means.
computer numeric control  (CNC) (n) See CNC.
computer-aided drafting/design  (CAD) (n) See CAD.
computer-aided manufacturing (CAM)  (n) See CAM.
computer-integrated manufacturing (CIM)  (n) See CIM.
concentricity  (n) In geometric dimensioning and tolerancing a condition in which all crosssectional elements of a cylinder, cone, or sphere are common to a datum axis.
conciseness  (adj.) A term used to describe one attribute of a CAD database. The more concise the database, the less space each record takes in the hard drive of the computer.
concurrent  (adj.) The technique of organizing numerous steps so that they happen in parallel rather than one after another (serially). Concurrent engineering, for example, involves all members of the design process working simultaneously in close coordination with each other rather than each member waiting for other members to finish with their components of the design.
cone  (n) A geometric solid described by a straight line (the generatrix), one end of which is attached to a fixed point (the vertex) and the other end of which traces a closed, curved path. The most common cone is a right circular cone, for which the curved path is a circle and the vertex lies on an axis that is perpendicular to the circle and through its center.
cone of vision  (n) A term used to describe the amount of space visible by the human eye looking in a fixed direction. The visible volume is approximately described by a right-angled cone for which the vertex is at the eye and the axis is aligned with the view direction.
conics  (n) Special case single-curved lines that can be described in many different ways: sections of a cone, an algebraic equation, and the locus of points. For our purposes, conics are sections of a right circular cone and include the ellipse, parabola, and hyperbola. The circle is a special-case conic.
connection list  (n) The list of all connections that need to be made between components on an electronic circuit board. This list is usually managed by the electronic CAD program.
connectors  (n) Devices used to join electronic components together to allow the transmission of signals. Connectors include plugs (external components) and jacks or receptacles (internal components) and can provide either temporary or permanent connections. Devices used for mechanical connection are typically called fasteners.
constraint  (n) A mathematical requirement placed on geometric elements in a 3-D model. Dimensional constraints define the distance between two geometric elements while geometric constraints define a relationship such as parallelism or perpendicularity between elements. The operator establishes an explicit constraint while the software automatically places an implicit constraint. A fully constrained feature has all of its geometry unequivocally defined while an underconstrained feature does not. An overconstrained feature has conflicting geometric requirements.
construction geometry  (n) Geometric elements that are used in the creation of a 2D drawing or 3D model but do not represent actual geometry of the virtual object being created.
construction lines  (n) Light, thin lines drawn to lay out the framework or structure of a drawing or sketch. Portions of these lines are often overdrawn with the final linework.
constructive solid geometry (CSG)  (n) A method of 3-D solid modeling in which geometric primitives are related to each other in a binary tree structure via Boolean operations. Each primitive is defined as a solid by a group of analytic surfaces (half-spaces), and the final object is defined by the calculation of the Boolean operations between primitives.
contour line  (n) A line that represents the independent variable (X,Y) combinations that result in a constant dependent variable value (also called an isoline). Acontour line can also represent the juncture between two surfaces of differing orientations or depths. In this definition, a contour line is an alternate term for edge.
contour plot  (n) A visualization in which the horizontal and vertical scales both represent independent variable values, and the contour lines show the mapping of constant, dependent variable values. Multiple contour lines are typically drawn on a plot, representing a uniform sampling of dependent variable values.
control points  (n) Points used in conjunction with spline curves. These points are not part of the curve proper, but the relationship between the control points and the points on the curve is used to define the shape of the curve.
controlling  (v) The procedures used to control materials, machines, and processes in the manufacturing and production cycle through automation, measuring, inspection, and testing.
conventional break  (n) A drawing symbol used to indicate that the object material continues past where the symbol is, but is not drawn. Conventional breaks are often used to reduce an overall dimension so that the object can be shown at a larger scale on paper or computer screen.
conventions  (n) Commonly accepted practices, rules, or methods. In technical drawing, a convention is the use of dashed lines to designate a feature hidden from the current viewpoint.
convolute  (n) A single-curved surface generated by a straight line moving such that it is always tangent to a double-curved line.
Coons’ surface  (n) A 3-D surface defined by input curves. This surface was named after Steven A. Coons, who developed the mathematical method for defining complex shapes used in the design of aircraft, automobiles, and ships’ hulls.
coordinate dimensioning  (n) A technique in which all dimensions are calculated as Cartesian X and Y distances from an origin point, usually located at the lower left-hand corner of the part. Also known as datum dimensioning or baseline dimensioning, coordinate dimensioning should be used cautiously because of the tolerance stackup that takes place.
coordinates  (n) A set of real numbers defining the location of a point in space. One value is given for each dimension of the space (i.e., 2-D, 3-D), and each value is determined by the point’s distance from the defined origin.
corner  (n) The nontangential intersection of two or more surfaces of an object. The intersection of two surfaces is usually referred to as an edge. Corners are represented on a drawing by either a single line or multiple co-terminating lines.
CPU  (n) Acronym for central processing unit. The CPU is the heart of the computer, coordinating all primary activities of the computer and processing a majority of operations or “calls” from the software. Computers are often classified by their CPUs. Examples are Intel’s Pentium™ and Motorola’s PowerPC™ 601.
crest  (n) A threading term describing the peak or top surface of a screw thread.
cross-hatch lines  (n) An alternate term for section lines. Cross-hatch often refers to section line symbols in which the lines cross each other rather than simply running parallel to each other.
curved line  (n) A line which does not follow a straight path. Curved lines are often classified by their underlying mathematical functions. Examples are circular and elliptical curves.
cutting plane  (n) An imaginary plane in space used to define the division between two parts of an object. Acutting plane is often used to define a portion of an object to be removed in order to reveal the interior detail.
cutting plane lines  (n) A line showing the location of a cutting plane in section drawings. The cutting plane line is drawn in the view for which the line of sight is parallel to the cutting plane. Arrows on the ends of the section line point toward the material to be retained in the corresponding section view.
cycle time  (n) The total time required for a process to take place.
cycloid  (n) A curve generated by the motion of a point on the circumference of a circle that is rolled in a plane along a straight line.
cylinder  (n) A planar geometric solid described by a straight line (the generatrix) that traces a closed, curved path and always stays parallel to itself. The most common cylinder is a right circular cylinder for which the curved path is a circle and the generatrix is perpendicular to the path.
cylindrical coordinates  (n) A system for locating points in space with one angle and two lengths. Cylindrical coordinates describe a point as a distance from the origin, its angle in the X–Y plane, and its Z value. Cylindrical coordinates are useful when designing circular shapes and geographic applications.
cylindricity  (n) A form control for geometric dimensioning and tolerancing. Cylindricity indicates that all points on the surface should be equidistant from a common axis. Unlike circularity, cylindricity refers to both the circular and the linear (longitudinal) elements on the surface.
data region  (n) The region in a visualization where the actual data is represented. In a graph or plot, the region would be bounded by the scales (axes) where the point or line markers representing the data are drawn.
data visualization  (n or v) The method or end result of transforming numeric and textual information into a graphic format. Visualizations are used to explore large quantities of data holistically in order to understand trends or principles.
datum  (n) A theoretically exact point, axis, or plane used as a reference for tabular dimensioning. A datum marks the origin from which the location and orientation of geometric features are established.
datum feature  (n) A term used in geometric dimensioning and tolerancing to describe a real or theoretical feature selected to ensure the proper orientation or location of other features on a part. Controls define features on the part relative to the datum features.
datum reference frame  (n) A term used in geometric dimensioning and tolerancing to describe the theoretical reference frame used to evaluate the location and orientation of features of a part. The frame consists of three mutually perpendicular (orthogonal) planes, which typically correspond to the principal planes of projection in a multiview drawing or the global coordinate system in a 3-D modeling system. In inspections, a physical surface may be established to simulate one of the reference planes.
declarative information  (n) A term used to describe the current state of an object. This type of information can be thought of as descriptive nouns. The location of a point in a coordinate system (8,3,5) is an example of declarative information.
density slicing  (n) A visualization technique, used with area and volume renderings, in which a particular data value or small range of values is highlighted in contrasting color. This technique can be used either for a single static image or for sequential images highlighting different data values in the image.
dependent variable  (n) A variable dependent on the response of the model and not controlled by the experimenter. Every dependent variable value is paired with one or more independent variables and represents the model’s response to the independent variable values.
depth  (n) One of the three principal dimensions of an object. The depth dimension is described in the right side and top views of a multiview drawing. The depth dimension is often associated with the Z axis in a 3-D modeling system. Depth can also refer to the distance cut into an object using a machining process (e.g., the distance measured between the crest and root of a thread normal to the axis or the depth of a drilled hole).
descriptive geometry  (n) The fundamental basis of the science of projection drawing, attributed to the work of Gaspard Monge (1746–1818). It is the basis of all types of 3-D representations on 2-D media used today.
design analysis  (n) The evaluation of a proposed design during the refinement process, using the criteria established in the ideation phase. The refinement stage is normally the second of three major phases in the design process.
design for manufacturability (DFM)  (n) A technique in which ways are found to simplify a design and reduce manufacturing costs. Using CAD/CAM technology, DFM determines the manufacturability of a design before it is produced.
design process  (n) The method used to create a solution to an engineering or technical problem. The result is often a product, either one of a kind or mass produced. The design process, though unique to each problem, typically includes standard stages and uses graphics to communicate information between and within these stages.
design visualization  (n) A process using the fundamental capabilities of a human visual system; the ability to perceive 3-D form, color, and pattern. Visualization is an analysis method used in the second stage of the design process, the refinement phase.
detail drawing  (n) A dimensioned multiview drawing of a single part, using ANSI standard conventions to describe the part’s shape, size, material, and finish. Detail drawings are sufficiently descriptive that the part can be manufactured using the drawing as the only communications device. Detail drawings are produced from design sketches or extracted from a 3-D computer model.
development  (n) An alternative description of the surfaces of a 3-D object as a 2-D pattern. The creation of a development is often thought of as an unfolding of the surfaces of an object. A developable surface, then, can be unfolded or unrolled onto a plane without distortion. Single-curved surfaces, such as cylinders and cones, are also developable.
deviation  (n) A tolerancing measure used to describe the difference between the size of a produced part and the basic size.
DFM  (n) See design for manufacturability.
diameter symbol  (n) A symbol used in ANSI dimensioning that precedes a numerical value, indicating that the value shows the diameter of a circle. The symbol used is the Greek letter phi (ø).
difference  (-) (n) The Boolean operation that subtracts, or removes, the intersecting geometry from the specified solid. For example, in the Boolean operation A - B, the intersection of solids A and B is removed from A.
diffuse  (adj.) A term describing a reflection of light that strikes a surface and reflects uniformly in all directions, creating no highlights or hot spots.
digital terrain model (DTM)  (n) A 3-D computer model of a land form generated from survey data. Such models are often used by civil engineers and land planners to explore possible placements of structures or changes to the terrain before actual construction begins.
dimension  (n or v) The physical size of an object, or the process of documenting physical sizes. The number of dimensions used to describe the object depends on whether length (1-D), area (2-D), or volume (3-D) is being measured. Dimensioning can also refer to the measurement of size, location, and orientation of particular features on an object.
dihedral angle  (n) The angle between two planes. Finding the true measurement of a dihedral angle requires an edge view of the two planes and is a common application for the use of auxiliary views.
dimension line  (n) A thin, solid line that shows the extent and direction of a dimension. Dimension lines are paired with the number representing the physical size of the feature, and extension lines are used to associate the dimension to the corresponding feature on the drawing.
dimetric projection  (n) An axonometric projection in which two of the three axes have the same scale and the same angle relative to the third axis. A dimetric drawing is less pleasing to the eye than a trimetric projection but is easier to draw.
direct data exchange  (n) A method of data exchange between CAD systems. Data is directly translated from the format native to one system to the format native to another system.
direct view  (n) A descriptive geometry technique (sometimes referred to as the natural method) that places the observer at an infinite distance from the object, with the observer’s line of sight perpendicular to the geometry in question. In third-angle projection, a projection plane is placed between the observer and the object, and the geometry is projected onto the projection plane.
directrix  (n) A line (typically curved) that describes the path of a straight line (the generatrix). The path of the generatrix along the directrix describes ruled surfaces or solids.
discretization  (v) The method of dividing more complex geometry into simpler geometry. A discretized model can be manipulated using techniques such as finite element analysis, in which all the simple geometric components of a model are evaluated simultaneously.
displacement  (n) The linear or angular distance moved by a part or mechanism. In cam design, a displacement diagram is used to chart the linear location of the follower relative to the angular position of the cam.
display devices  (n) The hardware used to display output text and graphics of computer software, such as CAD. The most common display device is the cathode ray tube, or CRT, used in computer monitors.
dither pattern  (n) A method of simulating varying value (gray) levels within an image when only one color of ink (usually black) is available. The patterns are achieved by grouping square matrices of pixels in an image (e.g., 3 × 3) and coloring a pattern of pixels in the matrix, based on the average value level in the matrix region. Because of the small size of the pixels relative to the size of the image, the pixel patterns give the impression of value changes when viewed at a distance.
document sketches  (n) A more formal type of freehand sketch used during the refinement stage of the design process. These sketches often contain many of the conventions found in more formal drawings.
domain  (n) A term that describes the types of objects that can or cannot be represented by a computer modeler. The larger the domain, the greater the number of objects the CAD system can describe.
donut  (n) See feed-through.
double-curved surface/line  (n) A surface or line that curves in two orthogonal dimensions at the same time. A sphere is an example of a double-curved surface.
double-line drawing  (n) See piping drawing.
drill drawing  (n) See fabrication drawing.
drawing exchange format  (n) See DXF.
drilling  (v) A process that uses a rotating cutting tool to produce holes. It can also refer more specifically to a process that produces holes using twist drill bits.
DTM  (n) See digital terrain model.
DXF  (n) Acronym for drawing exchange format, a nonproprietary CAD data format developed by Autodesk to facilitate the exchange of CAD-based graphic information. It has become a de facto neutral data exchange format for the microcomputer CAD industry.
dynamic analysis  (n) The evaluation of a design as it changes over time. Unlike kinematic analysis, dynamic analysis assumes that forces (e.g., gravity, angular momentum) are both acting on and created by the mechanism being analyzed.





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