Chapter 5 Key Terms

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. (See 265)
base feature	(n) The first feature created when defining a solid model. The base feature creates the initial geometry of the model from which additional geometry can be added or subtracted. (See 243)
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. (See 236)
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. (See 240)
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. (See 248)
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. (See 241)
construction geometry	(n) Any geometry created as part of the CAD modeling process that does not represent actual part geometry. Example of this would be workplanes, axes, or points used to locate geometry in a solid model. (See 245)
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. (See 236)
design intent	(n) A phrase describing the integration into the model of how feature dimensions and geometry relate to each other in order to satisfy the design constraints of the final product. Design intent is usually embodied in the model through the definition of features and their constraints. (See 241)
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 Aand B is removed from A. (See 236)
ergonomics	(n) A technical field concerned with optimizing the interface between humans and technology. The field has numerous specialties, including industrial safety and hygiene, human–computer interface design, and the design of control panels in manufacturing plants, cars, airplanes, etc. (See 281)
Euler operations	(v) Low-level operations used to construct models from geometric primitives, such as vertices, edges, and faces. The validity of the model is guaranteed by a simple mathematical formula, credited to both Leonhard Euler (1707–1783) and Jules Henri Poincaré (1854–1912). (See 240)
exploded assembly	(n) An assembly drawing, usually a pictorial, in which the parts of the assembly are spread apart (exploded) from their functional location in order to provide a larger, clearer view of the features of the individual parts. Flow lines are used to relate the parts to each other and to demonstrate assembly. This type of assembly drawing is used extensively for technical illustrations in such applications as parts catalogs and assembly instructions. (See 279)
feature	(n) A general term applied to physical portions of a part. Features typically serve a function, either in the final application of the part or in the specification or manufacture of it. Examples are a hole, slot, stud, or surface. (See 241)
feature tree	(n) A computer interface element common to most constraint-based solid modelers. The feature tree lists the geometric features contained in the model in order in which they are interpreted by the modeler. New features will typically be placed at the bottom of the tree. A feature in the tree can be construction geometry, part features, or components in an assembly. (See 263)
finite element modeling and analysis (FEM/FEA)	(n) An analysis technique used extensively to model and analyze forces within a computer model or a proposed design. In the modeling phase, the continuous surface or volume is discretized into a finite number of linked primitive geometries. In the analysis phase, the model is subjected to theoretical forces applied at certain locations, and the resulting forces are calculated across the rest of the model. (See 281)
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. (See 249)
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. (See 240)
intersection	(n) The Boolean operation in (U) which only the intersecting geometry of two solids remains. (See 236)
kinematic analysis	(n) The evaluation of a design as it changes over time. Of particular interest is multicomponent mechanisms in which parts move at varying rates through different volumes of space. The positions of the parts relative to each other at various points in time are studied through kinematic analysis. (See 280)
manifold models	(n) Models that unambiguously define a boundary between the inside and outside of an object. Solid modelers are usually restricted to manifold objects, whereas surface modelers often define unclosed, nonmanifold objects with no clear division between inside and outside. (See 235)
mass properties analysis	(n) Analytic techniques directly related to the geometric properties of an object. Typical calculations are the mass, centroids (center of gravity), and intertial properties of the object. In order to successfully use these techniques, the model must be able to unambiguously define the volume the object occupies and the density of the material within the volume. (See 280)
open loop	(n) A set of edges in a CAD model that does not connect end to end, creating a closed loop. Solid modelers differ as to whether open loops can be used as profiles for feature generation. Open loops cannot be used to define faces on a solid model. (See 248)
parent-child	(n) Describes the relationship orthogo-nal between features in a model. The parent is created first and the child feature is dependent on the parent feature for its definition in some way. An example would be that workplane might be the parent of a swept feature if the workplane was used in part to define the feature profile of the sweep. (See 263)
primitive	(n or adj.) A term used primarily to describe the fundamental geometric forms used for building 3-D CAD models. Primitives are typically defined parametrically or with singlesweep operations. Primitives are used as tool solids in Boolean operations. (See 235)
profile	(n) A form control for geometric dimensioning and tolerancing. A profile is the outline of a feature projected onto a plane. They usually consist of combinations of contiguous lines, arcs, and other curves. The profile tolerance zone may be made of a combination of straightness, roundness, parallelism, etc. (See 244)
profile sketch	(n) Typically a closed loop of lines drawn on a workplane as part of the feature definition process in 3-D modeling. In a constraint-based modeler, the profile sketch is constrained with dimensions and other geometric relations and then swept out to form a 3-D solid model feature. (See 248)
rapid prototyping	(n) A broad term used to describe several related processes that create physical models directly from a CAD database. Prototyping systems use a variety of techniques, including stereolithography and fused deposition modeling (FDM). Rapid prototyping is used to create prototypes for concept modeling, injection molds, and investment casting. (See 279)
relative coordinates	(n) Coordinate locations specified in reference to a previously defined location other than the origin. Relative coordinates are sometimes referred to as delta coordinates, meaning changed coordinates. (See 247)
solid geometry	(n) The geometry of 3-D objects, such as cylinders, cubes, and spheres, and their relationships. (See 235)
sweeping	(n) A 3-D modeling operation in which a closed polygon, called a profile, is drawn on the workplane (the U–V plane) and is transformed along a defined path. The sweeping technique is procedural in nature in that instructions are given as to how far and in what direction the sweep of the profile is to occur in order to create the solid. (See 244)
topological	(adj.) In 3-D modeling, a term that refers to the connectivity of the model, that is, how the elements of the object (i.e., the faces, edges, and vertices) are organized. Geometry specifies where elements are located in space and how they are shaped; topology describes how these elements are connected to each other. (See 248)
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. (See 236)
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. (See 266)
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. (See 280)
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. (See 279)
workplane	(n) Often called a construction plane, a 2-D infinitely large plane that can be oriented anywhere in 3-D space. Aworkplane 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. (See 245)
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. (See 245)