A rectangular surface defined by a grid of points which represent the control points of a Non-Uniform Rational B-Spline (NURBS) definition of a surface.
NURBS is a common mathematical representation in the CAD industry.
NURBS surfaces are not often used, because they are limited to a rectangular shape; trimmed surfaces are more useful.
Surfaces provide important information for meshing operations, enabling better meshes to be achieved than by using facet-based mesh input.
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