CATIA V5 曲面词典

只看该作者 · 发表于 2005-10-10 14:53:52

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Aesthetic: Pleasing in appearance. Used in context to describe styled (“Organic”) products.
Analytical: Separating something into component parts or constituent elements. Used in context to describe products that are primarily functional (“Mechanical”).
B-rep: Boundary Representation. The description of a 3D object’s shape, resulting from the assemblage of topological entities. See Topology.
Bezier: A type of spline curve named after its inventor, Pierre Bézier. Popular within the CAD/CAM and computer graphics industries because of their ease of manipulation. See Spline.
Points: Sometimes referred to as Control Vertices (“CV’s”). Suspended above or below the span of a curve or surface, control points establish a support lattice (“Control Polygon” or “Hull”) that defines and influences the curve or surface shape.
Cell: A single element (surface or curve) in CATIA V5 that has no visible discontinuities. For a curve, this implies no internal vertices; for a surface, no internal edges. See Continuity.
Conic: Mathematically, a curve that results from the intersection of a plane and a cone. In practice, conics are used to define smooth shapes that require analytical precision. Conics can be fully defined from only five pieces of information: beginning/end position, beginning/end tangency, and a parameter ranging between 0 and 1. Entities belonging to the conic family are: circle, ellipse, parabola, and hyperbola.
Continuity: The connection and/or smoothness between curve or surface segments. In mathematical form, continuity is the derivative of a curve(s) defining function, expressed as Cx. Beginning with C0 as positional connectivity, C1 implies tangent, C2 curvature, C3 rate of curvature, C4 rate of rate of curvature.
Foreign: In the context of CATIA V5, refers to geometry, e.g. IGES data, created in another CAD system. Foreign curves and surfaces have no associative (“parametric”) history.
Free form: A term used to describe geometry with little or no prismatic characteristics (straight lines, planar faces, etc.).
Hybrid: Refers to a mixed environment in which surface and solid modeling technique can be utilized to create geometry. In this context, CATIA V5 is a true hybrid modeling program.
Isoparm: Short for “Isoparametric Curve”. A line that exists on a surface, having a constant position along the latitude or longitude direction (“U” and “V”) of the surface. See U,V,W.
Loft: An ambiguous industry term used to describe (1) a surface consisting of multiple cross sections, (2) the act of creating free form shapes (“lofting”) or (3) the individual or department responsible for such activity (“loftsman”). The term is derived from the pre-computing age in which curvilinear shapes were manually drafted, often 1:1 scale. In the case of shipbuilding, these curves were too large for a drafting table; therefore this activity was often performed in the loft area of a large building. See Spline.
Manifold: A mathematical condition in which a sum of individual pieces of geometry can be defined in 3D space without ambiguity. It is typically used as a check for valid geometry in CATIA V5. A simple example would be a cross-section in the shape of an “X” (two intersecting lines). Such a shape cannot be offset or thickened as a whole because it is non-manifold.
Normal: In context, refers to a vector that is perpendicular to a curve or surface; much like the Z axis of an XY plane. Sometimes referred to as the “Porcupine”.
NURBS: Non Uniform Rational B-Spline. A robust mathematical form used to describe curves and surfaces. Almost any shape can be described with NURBS, including exact circles. Bezier curves are a special type of NURBS curves. See Bezier.
NUPBS: A term unique to CATIA, stands for Non Uniform Polynomial B-Spline. Also known as “NUPS”, the mathematics behind this type of curve is slightly different from NURBS in that it is non-rational. This means that the control points of a NUPBS curve all have the same amount of influence (“weight”) on the overall curve. In other words, modifying a single control point changes the entire curve vs. just having a local effect in the case of NURBS. Most curves in CATIA V5 are of this type. See NURBS, Control Points.
Patch: In context, a surface method of “filling” an area that has defined boundaries.
Point Cloud: A collection of XYZ points, usually collected with a scanning laser or light beam, that describes a 3D object. Often used in the process of reverse engineering a physical model. A supporting industry file format is ASC (ascii text).
Polygon Mesh: A set of polygonal faces (triangles) which represent the surface(s) of a 3D model. In industry practice, this type of data is commonly used for Stereolithography, or “rapid prototyping”. A supporting industry file format is STL.
Raster: A graphical image consisting of pixels or dots. Common industry file formats are BMP, JPG, and TIFF.
Segmentation: Splitting up a heterogeneous data set into subsets based on homogeneous characteristics. For curves and surfaces, this is typically based on curvature continuity. See Continuity.
Spine: The characteristic “backbone” of certain surface types, e.g. multi-section loft. A spine is used to define the position of a series of planes along its length, upon which curves are calculated that describe the surface.
Spline: Formerly a thin metal or wooden strip used by a draftsman that was held in place by weights positioned along its span. With the advent of computers, splines are now represented digitally, but serve the same purpose of defining curvilinear profiles. Beginning with “Cubic Polynomial Splines”, then “B-splines” (B stands for Basis), and then NURBS, we now have the mathematical equivalent of the former draftsman's tool. See NURBS.
Subdivision: A relatively new technology used to represent 3D models. Widely used in the computer graphics industry, e.g. Pixar Animation, a subdivision surface is actually a polygon mesh that is refined via smoothing algorithms to closely approximate a NURBS surface. Some believe this technology will replace NURBS modeling in the future. See NURBS, Polygon Mesh.
Surface: In context, refers to a 2D shape that defines the boundary of an object in three dimensions.
Tension: A force or stress causing stretching. In context, the amount of influence put upon a curve or surface by a tangency or curvature constraint.
Tessellate: The process of decomposing a curve or surface into a polygon mesh. See Polygon Mesh
Tolerance: The acceptable deviation from specification. A consequence of attempting to digitally model real world objects, tolerance is a persistent concern when using surfacing tools and technique. Often times, a design is iterated many times before it satisfies tolerance, continuity and segmentation requirements. See Continuity, Segmentation.
Topology: The physical anatomy of a 3D model. Primary topological elements are vertices, edges and faces.
Trim: In context, a relimitation of a surface or curve. Almost all surfaces intrinsically have four sides and do not allow holes. Irregular shapes and holes are created via trimming, sometimes automatically by the system if provided sufficient input parameters.
U,V,W: The coordinate system of a surface, expressed as a ratio of overall length ranging from 0 to 1 along each direction. In the case of a curve, only U exists. Akin to Cartesian XYZ space, U corresponds to the X direction, V to the Y direction, and W (usually referred to as the “normal”) to the Z direction.
Wireframe: A general term used in CATIA V5 to represent zero and one-dimensional geometry (points, planes, curves, etc.). A significant portion of time spent during the “surfacing” process is actually creating and modifying wireframe entities.
Vector: An entity that has magnitude and direction. In graphics form, a vector image is described by curves and algorithms. Supporting industry file formats are HPGL or DXF.