Overview
EN ISO 17450-4:2018 / ISO 17450-4:2017 - Geometrical product specifications (GPS) Part 4 - defines general rules for quantifying GPS deviations for individual geometrical characteristics. Published by CEN as the European adoption of ISO 17450‑4:2017, this standard explains how to transform local geometrical deviations into global characteristic values using formal quantifying functions. It is a general GPS document intended to be used across the ISO GPS matrix for consistent specification, measurement and reporting of geometric deviations.
Key topics and requirements
- Scope: General rules for quantifying GPS deviations for individual GPS characteristics (intrinsic and situation characteristics).
- Local geometrical deviation: Definition of local signed distance between a point on an input feature and the corresponding point on a reference feature (exists in a reference space).
- Reference space: Linear (A1) or areal (A2) spaces attached to the reference feature used to map local deviations.
- Quantifying function: Mathematical function that aggregates the complete set of local deviations into a single geometrical characteristic (can be rank‑order based).
- Rank‑order characteristics: Standardized types of global measures derived from local deviations, including maximum, minimum, average, median, mid‑range, range and maximum absolute deviation.
- Reference feature and datum relationships: Rules for using associated reference features as the basis for deviation evaluation; distinction between features unrelated to a datum system (intrinsic) and those related to a datum system (situation characteristics such as orientation and location).
- Local vs global deviations: Clarifies when deviations are treated locally (per point) and how they are combined to yield global characteristics.
- General applicability: Consistent conventions for reference extension, continuity assumptions and default decision rules (used with ISO GPS fundamentals).
Practical applications
- Use in metrology and quality assurance to define how measurements from CMMs, scanners or profilometers are aggregated into specification values.
- Supports tolerance specification, inspection reporting and conformity assessment in mechanical design and manufacturing.
- Helps standardize measurement algorithms used in coordinate measurement software, inspection plans and statistical process control.
- Applicable to: metrologists, quality engineers, CAD/CAM designers, inspection labs, manufacturing engineers and standards committees.
Related standards
- ISO 25378 - Definitions of GPS characteristics and conditions
- ISO 14638 - GPS matrix model (relationship and context)
- ISO 8015 - Fundamental GPS rules
- ISO 14253-1 - Decision rules for verifying conformity
Keywords: EN ISO 17450-4:2018, ISO 17450-4:2017, GPS, geometrical product specifications, quantifying GPS deviations, local geometrical deviation, quantifying function, rank-order characteristic, metrology, CMM inspection.
