ISO 16610-31:2016

Overview

ISO 16610-31:2016 - "Geometrical product specifications (GPS) - Filtration - Part 31: Robust profile filters: Gaussian regression filters" defines the characteristics of the discrete robust Gaussian regression filter used to separate long- and short-wave components of surface profiles that contain spike discontinuities (deep valleys and high peaks). The document specifies a regression filter of degree p = 2, combining a Gaussian weighting function with a biweight influence function to reduce the effect of extreme outliers while preserving form up to second degree. The filter is designated FPRG.

Keywords: ISO 16610-31:2016, robust Gaussian regression filter, profile filtration, GPS, surface texture, spike discontinuities, FPRG.

Key topics

• Scope and purpose: Evaluation of profile data with spikes for robust long/short separation.
• Filter type: Discrete regression filter (degree p = 2) with Gaussian weights and a biweight influence function (robust M-estimator).
• Weighting and robustness:
  • Space-variant Gaussian weighting function determined by cut-off wavelength (λ) and sampling interval (Δx).
  • Biweight influence function provides scale-invariant down-weighting of outliers; scale parameter c is defined (default ≈ three times Rq for Gaussian-distributed profiles).
• Profile modes: Separate filter equations and treatments for open and closed profiles.
• Nesting index / cut-off recommendations: Choose a nesting index equivalent to three times the feature width; suggested series includes 2.5 μm, 8 μm, 25 μm, 80 μm, 250 μm, 0.8 mm, etc.
• Transmission characteristic: Not provided - weighting depends on local profile values and position, so no universal transmission curve is defined.
• Designation: Filters following this standard use the code FPRG.

Applications

• Surface metrology and quality control: Robust separation of roughness from form on components with pores, burrs, pores, or spikes (ceramic, sintered, ground, turned, milled surfaces).
• Measurement software and algorithms: Implementing robust filtration routines for profilometers and analysis packages.
• Instrument manufacturers and calibration labs: Defining filter behavior for stylus or optical profilometry where extreme discontinuities bias standard linear filters.
• Engineering design & failure analysis: Characterizing functional stratified surfaces where extreme features must not dominate roughness parameters.

Related standards

• ISO 16610-1:2015 (Filtration overview and basic concepts)
• ISO 16610-20, ISO 16610-30 (profile filter foundations and other robust filters)
• ISO 14638 (GPS matrix model), ISO 8015 (GPS fundamentals)
• ISO 14253-1 (decision rules for conformity) and ISO 3274 (profilometer nominal characteristics)

ISO 16610-31:2016 is part of the ISO 16610 series on filtration and is intended for metrologists, quality engineers, software developers, and equipment manufacturers working with surface texture measurement and robust profile filtering.