ISO 16610-22:2015

Overview

ISO 16610-22:2015 is part of the ISO 16610 series on Geometrical Product Specifications (GPS) - Filtration. It specifies spline filters for linear profile filtration and explains how to separate a measured profile into its long-wave (low‑frequency) and short‑wave (high‑frequency) components. The standard defines filter equations for both non‑periodic (open) and periodic (closed) profiles and describes transmission behaviour, parameterization and implementation recommendations.

Key topics and technical requirements

• Filter basis: Spline profile filters based on cardinal cubic splines; the low‑pass result is a spline.
• Filter equations: Matrix formulations are provided for:
  • Non‑periodic spline profile filters (open profiles)
  • Periodic spline profile filters (closed profiles) These equations use matrices P and Q and require numerical solution (matrix algorithms).
• Parameters and notation: Key parameters include the cut‑off wavelength (λ), sampling interval (Δx), alpha (α = 1/(2 sin(π Δx / λ))) and the tension parameter (β, 0 ≤ β ≤ 1) which controls spline tightness.
• Weighting function: No simple closed form exists in general; numerical weighting functions are possible. An approximate continuous weighting function for the ideal cardinal cubic spline (β = 0) is given for small Δx.
• Transmission characteristics: Analytical approximations (for small Δx) for long‑wave and complementary short‑wave transmission are provided so users can assess filter frequency response.
• Recommendations and implementation: Guidance on nesting index (cut‑off choices), setting the tension parameter, and practical implementation including end‑effect handling and filter designation.

Practical applications and users

ISO 16610-22 is intended for:

• Metrology and quality‑control engineers performing surface texture analysis and profilometry
• Software developers embedding standard‑compliant filtration algorithms in measurement tools
• Instrument manufacturers and calibration labs implementing profile filtering for parts and components
• Designers and process engineers who need consistent separation of form, waviness and roughness for specification or process control

Practical benefits:

• Standardized, reproducible separation of long‑ and short‑wave components
• Usable for both open and closed profiles (spline filters can keep usable ends of open profiles, an advantage over some phase‑correct filters)
• Predictable transmission properties for frequency‑domain interpretation

Related standards

• ISO 16610‑1:2015 - Overview and basic terminology
• ISO 16610‑20:2015 - Linear profile filters: Basic concepts
• ISO 16610‑21:2015 - Linear profile filters: Gaussian filters
• ISO/IEC Guide 99 and ISO/IEC Guide 98‑3 (VIM & GUM) - measurement vocabulary and uncertainty

Keywords: ISO 16610-22:2015, spline filters, profile filtration, GPS, linear profile filters, cut‑off wavelength, tension parameter, sampling interval, transmission characteristic.