ISO 16610-21:2025

Overview

ISO 16610-21:2025 - "Geometrical product specifications (GPS) - Filtration - Part 21: Linear profile filters: Gaussian filters" specifies how to use linear Gaussian filters to separate and analyse surface profile components. It defines the Gaussian weighting function, the convolution-based filter equations, and the filter’s transmission behaviour (the Fourier transform of the weighting function). The standard covers both open and closed profiles (including roundness filtration) and provides implementation details and treatment of end effects in annexes.

Key topics and technical requirements

• Gaussian weighting function: Defines the shape and parameters of the Gaussian kernel used to compute the large-scale lateral component by convolution with a profile.
• Filter equations: Prescribes how to compute the large-scale lateral component (via convolution) and the small-scale lateral component (by subtraction).
• Cut-off wavelength (nesting index): The specified wavelength at which a sinusoidal component is transmitted at 50% - used to identify and designate the filter.
• Transmission characteristic: The Fourier transform of the weighting function; specifies attenuation vs. wavelength and is central to filter selection and interpretation.
• Open vs closed profiles: Distinguishes ideal (unbounded) open-profile treatment from practical finite-length open profiles; provides specific implementation guidance for closed (periodic) profiles, including roundness and generalized closed profiles (re-entrant features).
• Implementation details: Annex A (open profiles) and Annex B (closed profiles) give practical guidance for numerical implementation and handling of end effects.
• Series of nesting index values and filter designation: Guidance on standard cut-off values and how to reference filters unambiguously in specifications.

Practical applications and users

ISO 16610-21 is essential for professionals working with surface metrology, where profile filtering is needed to separate roughness, waviness and form components:

• Metrologists and quality engineers specifying or verifying surface texture requirements.
• Manufacturing engineers assessing machining, grinding, or finishing processes.
• Software developers and instrument manufacturers implementing profile-analysis algorithms (profilometers, roundness instruments, surface-analysis software).
• R&D and academic researchers studying surface functional performance (friction, wear, sealing). The standard ensures consistent, reproducible filtration results and clear communication of filter parameters in technical documentation and conformity assessment.

Related standards

• ISO 16610-1 - Filtration: Overview and basic concepts
• ISO 16610-20 - Linear profile filters: Basic concepts
• ISO 14638 / ISO 8015 - GPS matrix and fundamental GPS rules (context and decision rules)
• ISO/IEC Guide 99 (VIM) - Metrology terminology

ISO 16610-21:2025 is part of the ISO 16610 series for profile filtration and should be used alongside the series’ other parts for comprehensive GPS-compliant surface specification and verification.