Design and CAD glossary

A plain-language glossary of the surfacing, CAD and AI reconstruction terms used across automotive and industrial design: NURBS, Class A surfaces, curve networks, patch layout, retopology, IGES, STEP and more.

NURBS: Non-Uniform Rational B-Splines: mathematically defined curves and surfaces used by CAD systems. Unlike meshes, NURBS surfaces are resolution-independent and editable through control points, which is why manufacturing CAD is built on them.
Class A surface: An exterior surface built to the highest continuity and reflection-quality standard, typically curvature-continuous (G2 or better). Used for visible automotive bodywork and premium consumer products.
Curve network: The structured grid of primary and secondary curves that defines a surface model. Patch quality depends almost entirely on how the curve network is laid out.
Patch layout: The arrangement of four-sided regions across a curve network that each become a NURBS patch. A clean layout gives predictable continuity across boundaries.
Retopology: Rebuilding a mesh with cleaner, usually quad-dominant topology. Required before reliable UV mapping, subdivision or surface fitting.
Orthographic views: Side, front, rear and top projections without perspective distortion. They are the standard input for reconstructing accurate 3D geometry from 2D imagery.
Image-to-3D: Reconstructing a 3D mesh from one or more images. Multi-view input yields more accurate proportions than a single image.
IGES: A neutral CAD interchange format that carries NURBS curves and surfaces. Widely used to move surface data between Alias, Catia, NX and Rhino.
STEP: ISO 10303 neutral CAD format carrying solids and surfaces with more structure than IGES. The default choice for engineering interchange.
CMF: Colour, Material and Finish: the specification layer that defines how a designed form is finished in production.
Zebra / diagnostic shading: Striped reflection analysis used to inspect surface continuity. Breaks or kinks in the stripes reveal continuity defects at patch boundaries.
Parametric morphing: Adjusting a model through named dimensions such as wheelbase, overhang or ride height, regenerating only the geometry affected by the change.
SubD: Subdivision surfaces: a smooth surface defined by refining a coarse control cage. Common in concept modelling and convertible to NURBS for CAD.
Watertight mesh: A mesh with no holes or boundary edges, so it encloses a volume. Required for 3D printing, simulation and reliable surface fitting.