Geometric design (GD), also known as geometric modelling, is a branch of computational geometry. It deals with the construction and representation of free-form curves, surfaces, or volumes. Core problems are curve and surface modelling and representation. GD studies especially the construction and manipulation of curves and surfaces given by a set of points using polynomial, rational, piecewise polynomial, or piecewise rational methods. The most important instruments here are parametric curves and parametric surfaces, such as Bézier curves, spline curves and surfaces. An important non-parametric approach is the level set method.