Glossary of Terms
The following sections define many of the basic terms and concepts you should know in order to use rapidform effectively.
A | B | C | D | E | F | G | H | I | L | M | N | O | P | R | S | T | U | V | W
ACIS
A component software that
provides a solid modeling "engine" (also called
"kernel") used by many
commercial and research organizations as the core of
CAD/CAM/CAE applications.
Creates models in the SAT format. (Note: ACIS is
not an acronym). (Spatial
Technology Corp.)
Anti-aliasing
Anti-aliasing is sub pixel interpolation, a technique that makes edges appear to
have better resolution.
API
API (Application Programming Interface) is a series of functions that programs can use to make the operating system do their dirty work. It serves as a software interface to be used by other programs.
Aspect Ratio
Ratio of width to height
Bezier Curve(Surface)
A smooth curve controlled by three or more
control points.
The Bezier
curve always intersects the first and last
control point,
but is usually only influenced by the others.
The Bezier surface is an extension of the Bezier curve.
Named after its inventor, Pierre Bézier, a CAD system designer
in France.
Bitmap
A Bitmap is a pixel by pixel image.
Boundary
Borders of a model
Boundary Edge
Edge of a polygon that is not shared with another polygon
Boundary Representation (B-rep)
A solid modeling database structure that defines and stores a solid as a topological set of explicitly defined vertices, edges, and faces.
Box
A closed box composed of three pairs of rectangular faces placed opposite each
other and joined at right
angles to each other, also
known as a rectangular parallelepiped.
C0 or G0 Continuity
Positional continuity. Two surfaces that share a set of boundaries are C0 or G0 continuous when the adjoining edges of the surfaces match up exactly with respect to surface position.
C1 or G1 Continuity
Tangential continuity. Two surfaces that share a set of boundaries are C1 or G1 continuous when the normal at the boundaries of those surfaces are exactly aligned in direction and are the same in magnitude.
C2 or G2 Continuity
Curvature continuity. Two surfaces that share a set of boundaries are C2 or G2 continuous when they have the same curvature values where they meet.
CAD
Computer Aided Design
Centroid
The centroid (sometimes called a center of gravity) is the center point or middle point of the area. Traditionally, this point is found by cutting the area out of cardboard and balancing it on a pin. The balance point location is the centroid.
CMM
Coordinate Measuring Machine
Control Points
A set of points that parameterize and control the shape of a NURBS curve or surface
CT
CT (Computed Tomography) scans measure photon linear attenuation of a tissue relative to water. These scans produce high-resolution anatomic images because the contrast between soft tissue and skeletal structures such as calcifications and bone are easily seen with this modality and has a spatial resolution of about 1 mm.
Curvature
This is a mathematically-defined term which refers to the amount of roundness located at a point on a curve or surface. If a curve is flat, then its curvature is zero. As the curve becomes more rounded, the radius of curvature goes down and the curvature goes up. Curvature 'k' = 1 / rho, where rho is defined as the radius of curvature. These two values ('k' and 'rho') are inversely related.
Curve
A curve is a mathematical function that describes the path of a point moving through space. In rapidform, curves are displayed by sampling the mathematical description of the curve at specified intervals, then drawing line segments between these sample points. rapidform uses NURBS to represent the curve geometry.
Decimation
An operation that reduces the count of entities. This operation usually attempts to preserve the object's overall shape and sharp features.
Depth Cueing
Depth cueing is the lowering of intensity as objects move away from the
viewpoint.
DICOM
The Digital Imaging and Communications in Medicine (DICOM) standard was created by the National Electrical Manufacturers Association (NEMA) to aid the distribution and viewing of medical images, such as CT scans, MRIs, and ultrasound.
Displacement map
A function defined on NURBS surfaces that depicts the deviations between a NURBS surface and the original polygonal mesh.
Draft Angle
The amount of angle required to permit release of the part from the tool, measured from the die removal angle.
Edge
Line between two connected vertices on a polygon
Face
A face is a triangle composed of three vertices, and it is defined as three edges connected with each other.
Feature
In rapidform, the base feature can be an analytic shape such as planes(including box), a sphere, cylinder, or cone. And the advanced feature can be one of a hole, cut, fillet, chamfer, or an extrusion, a revolution, or a free-form shape such as a sweep or loft.
Feature Curve
Curve that maintain characteristics in the feature topology of a model
Feature-based modeling
Modeling technique in which you design the part by applying features that are similar to how the part is manufactured (e.g., holes, ribs, fillets, cuts, and bosses)
Flat Shading
The flat shading method is also called constant shading. For rendering, it
assigns a uniform color throughout an entire polygon. This shading results in
the lowest quality, an object surface with a faceted appearance and a visible
underlying geometry that looks 'blocky'.
Gaussian
Curvature
The double curvature of a
point on a surface. If a surface is developable (flat in one direction), then
the Gaussian curvature is zero. As the surface becomes more curved in two
directions (twisted), the Gaussian curvature increases (positively or
negatively). Mathematically, the Gaussian curvature is the product of the two
principal curvatures.
Geometric
Dimensioning and Tolerancing (GD&T)
Geometric dimensioning and
tolerancing (GD&T) is a language used on mechanical engineering drawings
composed of symbols that are used to efficiently and accurately communicate
geometry requirements for associated features on components and assemblies.
Geometric
Tolerance (GT)
A geometric tolerance describes the degree to which a nominal design feature can
vary while satisfying functional requirements.
It also describes the
variation that is allowed when fabricating parts from a design. Manufacturing
processes have particular and repeatable ranges of variation. The tolerance
associated with a process depends on expected process variation and the
techniques used for measurement.
In rapidform, flatness, straightness, circularity and etc are defined as GT.
Gouraud Shading
Gouraud shading, one of the most popular smooth shading algorithms, is named
after its French originator, Henri Gouraud. Gouraud shading, or color
interpolation, is a process by which color information is interpolated across
the face of the polygon to determine the colors at each pixel. It assigns color
to every pixel within each polygon based on linear interpolation from the
polygon's vertices.
Grid
A tessellation of congruent squares sometimes used to measure distance
GUI
Graphic User Interface
Hidden lines
Broken lines used to signify lines that normally wouldn't be seen in a drawing
Healing
A series of functions whose purpose is to correct geometric abnormalities contained within a surface or solid model. Common functions may include surface simplification (mapping spline surfaces to analytic shapes such as planes, cylinders, cones, etc.), face stitching, and edge gap repair. More advanced functions may include the ability to merge coincident vertices, repair self-intersections, and reduce and/or redeploy curve and surface control nodes. Programs typically perform healing on geometry that you import through neutral formats such as IGES, STEP, and SAT with problems caused by conditions ranging from imprecise geometric definitions to poor entity mapping to poorly written translator code. A CAD system may perform healing externally (on the neutral file), as it imports the neutral file, or internally after the neutral file is imported.
Hybrid
Solid modeling system that employs two or more distinct database structures (e.g., CSG and B-Rep) to store and define a solid. Hybrid systems are known for their ability to mix advanced surfacing and solid functions within the same database. Hybrid systems may also let you explode a solid, perform surface and solid functions on open volumes, and then sew the faces back into a solid.
IGES
Initial Graphics Exchange Specification, the standard for exchanging geometric information
Interpolation
The process of defining a curve (or surface) that passes through a set of points.
Isocurve(Iso-parameter curve)
A set of curves on the surface that occur in the UV direction and define the surface shape. A parametric surface is typically crossed with flow lines that are constant U or V parameter curves on the surface, which are referred to either as isocurves.
LMB
Left Mouse Button
Loop
A set of curves with ends that meet
Manipulator
An interactive control device, which is usually used to transform an object
Model
A model is a logical set of several shells. Only one model can exist on the workspace window.
Mouse Drag
Moving the mouse while pressing and holding the mouse button.
MRI (Magnetic Resonance Imaging) scans acquire highly detailed anatomic information. Magnetic pulse sequences highlight the different amounts of water (hydrogen protons) contained in anatomical structures and fluids.
Noise
Erroneous data resulting from the scanning process. Usually represented as unnecessary points in a point cloud.
Normal
A vector perpendicular to a polygonal mesh
NURBS
Non-Uniform Rational B-Spline. This is a type of spline where the curve passes close to but not through the control points or knots and used in spline-based modeling.
OLE
OLE (Object Linking and Embedding) allows users to integrate data from different applications. Object linking allows users to share a single source of data for a particular object.
Parameter
For B-splines, this refers to the independent value or parameter that is used to define the curve or surface. For curves, the parameter is called 'u' and its value changes from 0.0 at one end of the curve to 1.0 at the other end. Rectangular-like B-spline surfaces have two parameters: constant 'u' for the row direction and constant 'v' for the column direction. Their values also range from 0.0 to 1.0, so that every combination of 'u' and 'v' values between 0.0 and 1.0 define the entire surface.
Parasolid
A solid modeling engine used by many commercial and research organizations as the core of CAD/CAM/CAE applications. (Unigraphics Solutions Inc.)
Parameterization
The flow of the curves defining a parametric surface
Patch
A portion of a surface defined by a set of control points. The program allows you to deal with the surface on a patch-by-patch basis.
Perspective view
A view in which perspective can be observed. Perspective views are used to give a 3D appearance.
Phong
Shading
Phong shading is a sophisticated smooth
shading method, originated by Phong Bui-tuong. The Phong shading algorithm is
best known for its ability to render precise, realistic specula highlights.
During rendering, Phong shading achieves excellent realism by calculating the
amount of light on the object at tiny points across the entire surface instead
of at the vertices of the polygons. Each pixel representing the image is given
its own color based on the lighting model applied at that point. Phong shading
requires much more computation for the hardware than Gouraud shading.
Point Cloud (or Point Set)
A point cloud is defined as a set of points in 3D space. A point cloud may consist of a single point or several million points. In rapidform, the number of points in a point cloud is limited only by the memory limitations of the host computer.
Polyline
A collection of n lines defined by the n +1 points that define the endpoints of each line segment
Polygonal model
A model composed of polygon faces.
Primitives
Pre-defined objects, either 2D or 3D, i.e., circle, square, arc, plane or sphere, cube, cylinder, cone, torus, and various polyhedrons.
Profile
A 2D sketch drawing on a reference plane.
Propagate
The process of creating equal numbers of isocurves across the boundary of two or more adjacent surface patches along the boundary's perpendicular direction
Region
A region is a user-selected set of vertex or face, which is just a temporary set in the job process. A region is released after the corresponding job is finished.
Rendering
The process of creating life-like images on a screen using mathematical models and formulas to add shading, color, and lamination to a 2D or 3D wireframe
Reverse Engineering
In general, the processing of understanding the design and funtionality of a product using a sample of the product itself. For CAD, the term refers more narrowly to the process of scanning or digitizing the shape of an object and turning that data into a model which can then be treated as a normal CAD model, ultimately to re-manufacture the part or product.
RMB
Right Mouse Button
RP (Rapid Prototyping)
A various manufacturing processes as well as a burgeoning industry. RP processes involve devices--ranging from office modelers to four-ton machines--that accept 3D CAD files, slice the data into cross-sections, and construct layers from the bottom up, bonding one on top of the other, to produce physical prototypes for applications such as engineering form, fit, and function; soft tooling for prototypes; and patterns for hard tooling. The RP industry consists of RP systems, materials, and after-market products as well as a services sector.
SAT
A file format for 3D solid geometry, created by systems that use the ACIS solid modeling engine. (Spatial Technology Corp.)
Shell
A shell is a logical set of several faces. Faces are usually connected with each other, but not always. Normally, polygon meshes obtained through triangulation process of a point cloud measured on one view are managed as a shell.
Shell curve
Curves that are automatically connected to a shell when they are created
Shell surface
Surfaces that are automatically connected to a shell when they are created
Sketch
2D geometry, such as lines, arcs, circles, and curves, used to drive geometric features. The sketch environment contains a constraint manager that lets you place dimensional and relational constraints on geometry.
SLA
The 3D file format used by Stereolithography Apparatus (SLA) rapid prototyping machines. Can also be used as a general 3D file format for viewing. (3D Systems Inc.)
Space curve
Curves that are not connected to any shell. Space curves can be usually generated by importing foreign data formats such as IGES, STEP or VDAFS.
Space surface
Surfaces that are not connected to any shell and operations related to shell are not available. Space surfaces can be usually generated by importing foreign data formats such as IGES, STEP or VDAFS. They may be introduced by generic surface creation tools such as blend, loft, sweep, and N-boundary filling.
STL(Stereolithography)
Stereo Lithography file format. A rapid prototyping (RP) process, introduced in 1987 by 3D Systems Inc. launched the RP industry. A Stereolithography Apparatus (SLA) machine builds physical models in this manner: it focuses an ultraviolet (UV) light onto the surface of a vat filled with liquid photopolymer. The light beam, moving under computer control, draws each layer of an object onto the surface of the liquid. Wherever the beam strikes the surface, liquid changes to solid. 3D parts are built from the bottom up, one layer at a time; when the part is finished, it is exposed to UV light for curing. (3D Systems Inc.)
STEP
The Standard for the Exchange of Product Model Data is a comprehensive ISO standard (ISO 10303) that describes how to represent and exchange digital product information.
Surface (Patch)
A surface is defined as a mathematical function that describes the geometry fit to polygonal meshes. A surface(called patch) is bounded by iso-parameter curves(called flow line), controlled by a selected set of control points in the bi-direction, U-direction and V-direction. The surface is divided into 2 types, untrimmed and trimmed surface. The untrimmed surface has 4 boundary curves, while the trimmed surface has 2, 3, or more than 4 boundary curves. The trimmed surface is a special type of surface that is trimmed by its boundary curves after a basic surface, that is, an untrimmed surface is generated. rapidform uses NURBS to represent the surface geometry.
Template
A function that copy, save, and reuse layouts. Thus, you can copy and use them on other parts of the same model.
Tessellation
Tessellation is the process of subdividing a surface into smaller shapes. To describe object surface patterns, tessellation breaks down the surface of an object into manageable polygons. Triangles or quadrilaterals are two usually used polygons in drawing graphical objects because computer hardware can easy manipulate and calculate these two simple polygons.
Texture Mapping
Texture mapping is based on a stored bitmap consisting of texture pixels, or
texels. It consists of wrapping a texture image onto an object to create a
realistic representation of the object in 3D space.
Toggle
To switch from one setting to another. The term toggle implies that there are only two possible settings and that you are switching from the current setting to the other setting.
Toolbar
Movable palette of tools that perform operations
Topology
Data that tells the software how to connect the entities
Torsion
A twisting deformation of a body about an axis in which straight lines that are initially parallel to the axis become helixes. In mathematics, it is defined by the magnitude of the derivative of the normal to the plane of curvature with respect to distance on the curve.
Torus
A torus is a surface having a single hole. The usual torus embedded in three-dimensional space is shaped like a donut, but the concept of the torus is extremely useful in higher dimensional space as well. In general, tori can also have multiple holes.
Transformation
Change of coordinates; a series of mathematical operations that act on output
primitives and geometric attributes to convert them from modeling coordinates to
device coordinates.
Undercut
A face that is oriented opposite to the direction in which the mold will be pulled.
UV Direction
Each surface patch has two directions, U and V. Isocurves within a patch run in U or V direction.
VDAFS
Vereinung Deutsche Automobilindustrie Flächen Schnittstelle is a German neutral file format for the exchange of surface geometry. It was developed to exchange free form surfaces and it became a DIN standard in 1986. VDAFS supports elementary curve and surface geometry entities and some topology to define more complex models.
Vertex
A single point defined by its Cartesian coordinates(X, Y and Z)
Voxel
A voxel is an element in a 3D volume. A voxel is the 3D equivalent of a picture element, or pixel. It is also defined as the smallest discrete spatial component of a digital volume.
VRML(Virtual Reality Modeling Language)
A language that lets Web browsers view and interact with 3D models; requires a special viewer.
Wireframe
A geometric model that describes 3D geometry by outlining its edges.
World Coordinates
In 3D space, a coordinate system that enables the software and the artist to establish an exact location for objects, lights, or cameras. The origin of the world coordinate system is (0, 0, 0).