This document specifies linear spline filters for the filtration of surface profiles. It defines, in particular, how to separate large- and small-scale lateral components of surface profiles.

The concepts presented for closed profiles are applicable to the case of roundness filtration. Where appropriate, these concepts can be extended to generalized closed profiles, especially for surface profiles with re-entrant features.

Examples for the application of the spline filter are given in Annex A. The influence of the tension parameter  on the large-scale lateral component of the profile is shown in Annex B.