Absolute Coordinates
The location of a point in terms of distances and/or angles from a fixed origin.


Annotation
The text included on a drawing such as notes, instructions, dimensions, etc. In today's 3D modeling systems, annotation text can also be placed on a datum plane or planar face.


ANSI
Acronym for the American National Standards Institute. Founded in 1918, ANSI is a voluntary organization composed of over 1,300 members (including all the large computer companies) that creates standards for the computer industry.


Array
A rectangular or circular pattern of graphical objects. The objects can be wireframe entities, surfaces, features, components or another pattern.


Assembly Modeling
Process by which individual solid (or surface) models are brought together to form an assembly model. The original geometry file of each model (component) resides outside the assembly and is instanced (referenced) into it.

In a bottom-up assembly design, complex assemblies are broken down into smaller sub-assemblies and components, modeled separately, and then instanced into the final assembly.

In a top-down assembly design, all components are modeled within the context of the assembly. In either approach, each component part eventually resides within a separate model file, but can be activated for editing from within the context of the assembly. This is referred to as "In Context Assembly Modeling."


Automatic Mesh Generation
In Finite Element Analysis (see FEA), a function that automatically generates a mesh of elements from a 2D or 3D structure. Shell elements are usually used for surface models, and solid elements are used for solid models.


Boundary Prepresentation (B-Rep)
Acronym for Boundary Representation. A 3D modeling database structure that defines and stores a solid (open or closed) as a topological set of explicitly defined vertices, edges, and faces. The B-Rep database structure is used by virtually all commercially available 3D CAD systems today. (See also CSG)


Base Feature
The first feature created to start a new part model. The base feature can be an analytic shape such as a box, sphere, or cone, or a free-form shape such as a sweep or loft. The base feature chosen should define as much of the overall shape of the part as possible to keep the total number of operations to a minimum


Bit Map
The digital representation of an image in which bits are referenced (mapped) to pixels. In color graphics, a different value is used for each red, green, and blue component of a pixel. In advanced rendering, a bit map image can be used as a texture map attribute that is applied to a surface or plane. In 3D modeling, a bit map image can be embossed onto a surface where each pixel in the map determines the height of the surface at that location.


Boss Feature
Any feature that adds material to the model.


Bottom-Up Assembly Design
(See Assembly Modeling)


Buffer
(see Frame Buffer)


Cartesian Coordinate System
(See Coordinate System)


CGM
The acronym for Computer Graphics Metafile. CGM (ISO/IEC 8632:1999) is a format defined by the International standard ISO/IEC 8632:1999 for digitally describing vector, raster, and hybrid (raster and vector) graphic pictures compactly. For example, the technical illustrations in electronic documentation, geophysical data visualization, and other 2-dimensional graphics presentation applications. See also ISO.


Chamfer
A beveled edge or corner between two otherwise intersecting lines or surfaces.


Closed Profile
A 2D sketch or a group of attached planar curves whose perimeter profile forms a closed loop. Until recently, all feature based sketches had to form closed profiles. Today's 3D modeling systems are intelligent enough to support open profiles by determining how to close the profile during construction. The closure technique used can be system defined or user defined.


Configuration
A particular grouping of computer hardware as a functional unit. It may also include the allocation of hardware resources and sometimes refers to software parameter settings.

In today's assembly modeling applications, configuration refers to a particular group of components in a family of components. An assembly can have multiple configurations that reference alternate components.


Control Key
A key on the keyboard used in conjunction with other keys to perform special functions.


Coordinate System
Geometric relation used to denote the location of a point in 3D space. The most common is the Cartesian or rectangular coordinate system, whereby points are located by traversing the x-, y-, and z-axes of 3D space. Normally the origin of the coordinate system is defined as 0,0,0. Other coordinate systems can more easily express the coordinates of specific geometric shapes. For example, you can use a spherical coordinate system to locate points on the surface of a sphere and a cylindrical coordinate system to locate points on the face of a cylinder.


Crosshairs
A cursor usually made up of two perpendicular lines on the display screen used to select coordinate locations.


CSG
Acronym for Constructive Solid Geometry. CSG is database structure that was used in early solid modeling systems. It defines and stores a solid as a series of unions, intersections, and differences of analytic or freeform shapes by Boolean techniques.

The topology of a CSG solid is implicitly defined (that is, the intersecting boundaries are mathematically implied). CSG is no longer used by viable commercial systems today because of its inability to support complex blends and shapes. The B-Rep database structure of today's 3D modeling systems can define CSG like operations using Boolean techniques.


Cursor
A pointer on a video display screen that can be moved around and is used to place textual or graphical information.


Curve Fitting
The process of passing arc segments through a number of control points to create a curve.


Curve Smoothing
The process of curve or surface approximation using polynomial equations to generate a curve that passes near, but not always through, a set of control points or mesh vertices.


Cut Feature
Any feature that removes material from the 3D model.