An extension of the quartic Wang–Ball closed curves with a given tangent polygon

An algorithm for constructing an extension of the close quartic Wang–Ball curves, which are tangential to the given polygon, is described. The control points of an extension of the close quartic Wang–Ball curves to be constructed are computed simply by using the vertices of the given polygon. The constructed curves are shape-preserving to the polygon. The local modification to the extension of the close quartic Wang–Ball curves can be completed by simply adjusting the corresponding control parameters. One example is also given.