A geometric constraint on curve networks suitable for smooth interpolation

A key problem when interpolating a network of curves occurs at vertices: an algebraic condition, called the vertex enclosure constraint, must hold wherever an even number of curves meet. This paper recasts the vertex enclosure constraint in terms of the local geometry of the curve network. This allows formulating a new geometric constraint, related to Euler’s Theorem on local curvature. The geometric constraint implies the vertex enclosure constraint and is equivalent to it where four curve segments meet without forming an X. Also the limiting case of collinear curve tangents is analyzed.