Overview
ISO 14406:2010 - "Geometrical product specifications (GPS) - Extraction" establishes the basic terminology, concepts and framework for GPS extraction used in surface metrology and dimensional verification. The standard formalizes how a workpiece’s functional surfaces (skin model, mechanical surface, electromagnetic surface) are represented as a primary surface and how discrete measurements produce a primary extracted surface for digital processing. ISO 14406 introduces the concepts of sampling and reconstruction for extraction and documents principal sampling schemes for basic geometries.
Key topics and technical requirements
- Terminology and models: Definitions for skin model, real surface, mechanical/electromagnetic surfaces, integral features, primary mathematical model, nesting index and degrees of freedom.
- Primary extracted surface & reconstruction: Formalizes the extracted data set (finite sample points) and the notion of reconstruction - choosing a primary mathematical model of fixed nesting index that passes through sampled points.
- Sampling vs. aliasing: Explains sampling aliasing when multiple primary mathematical models fit the same sampled data and highlights the need to choose sampling so reconstruction is reliable.
- Wavelets (exact reconstruction): For linear primary mappings (e.g., wavelet-based multi-resolution), the standard references exact-reconstruction theorems analogous to the Nyquist criterion: the number of sampling points must meet or exceed the degrees of freedom to avoid information loss.
- Morphological filters (zone of possible reconstruction): For non-linear operators (morphological filters), there is no universal Nyquist-equivalent; instead the standard describes limits on information loss (zones of possible reconstruction) and sampling considerations for structuring elements (e.g., circular disk, horizontal line).
- Sampling schemes catalogued: Practical sampling patterns are listed, including orthogonal grids (including polar/birdcage variants), specified grids, stratified, helix, spiral, spider web and points method.
Applications and who uses it
ISO 14406 is applicable to professionals and organizations involved in:
- Metrology and inspection labs - defining measurement strategies and data acquisition for surface characterization.
- Quality and manufacturing engineers - selecting sampling intervals and schemes to ensure reliable reconstruction and conformity assessments.
- CMM, profilometer and optical scanner vendors - implementing acquisition modes and reconstruction algorithms in hardware/firmware.
- CAD/CAM and metrology software developers - integrating sampling, filtering and reconstruction routines consistent with GPS.
- Standards bodies and accreditation - harmonizing terminology and procedures across GPS matrix standards.
Practical benefits include improved traceability of measurement workflows, reduced sampling aliasing risk, and clearer guidance on choosing sampling patterns that support accurate digital filtering and parameter computation.
Related standards (normative)
Keywords: ISO 14406:2010, GPS extraction, sampling and reconstruction, surface metrology, primary extracted surface, wavelets, morphological filters, sampling schemes, Nyquist.
