SRFPACK is a Fortan 77 software package that constructs a smooth interpolatory or approximating surface to data values associated with arbitrarily distributed points in the plane. It employs automatically selected tension factors to preserve shape properties of the data and to avoid overshoot and undershoot associated with steep gradients. The domain of the fitting function may be nonconvex or multiply connected, and the surface may be constrained to have discontinuous value or derivative across a user-specified curve representing, for example, a geological fault line. Although triangle based, the method provides a means of avoiding the inaccuracy associated with long thin triangles on the boundary of the convex hull of the data abscissae. (Source:

This software is also peer reviewed by journal TOMS.