EN ISO 25378:2011 PDF

Overview

EN ISO 25378:2011 - Geometrical product specifications (GPS) - Characteristics and conditions - Definitions defines the general vocabulary and mathematical descriptions for geometrical specifications, characteristics and conditions used in GPS. The standard provides a consistent, model-based set of definitions (using the mathematical approach from Annex B of ISO 17450‑1:2011) that map out requirements for future standardization, tools and software - rather than serving as a direct design handbook for industrial use.

Key points:

• Establishes formal definitions for geometrical characteristics and conditions.
• Uses a mathematical model and the concepts of operators and the duality principle.
• Applies to a workpiece, an assembly, a population of workpieces, and a population of assemblies.
• Not a specification of GPS symbology or expression formats.

Key Topics and Technical Requirements

• Geometrical specification: an expression of one or more conditions on geometrical characteristics (individual or population specifications).
• Condition: defined as a combination of a limit value and a binary relational mathematical operator (examples in the standard include expressions like “≤ 6.3” or ranges such as 9.8 ≤ X ≤ 10.2).
• Individual condition vs. population condition: individual applies to each workpiece; population applies to the statistical or aggregated value of a population characteristic (used for SPC).
• Operators and duality principle: specification operators are described so they can conceptually be used either as specification operators or as verification operators.
• Three “worlds”: nominal definition (designer’s ideal), specification (imagined representations used to define requirements), and verification (measured representations and mathematical/physical operations).
• Mathematical vs. physical operations: standard distinguishes mathematical treatments (computational sampling or electronic processing) from physical measurement methods (mechanical, optical, electromagnetic).

Practical Applications - Who Uses ISO 25378:2011

• Standards committees and technical writers - to harmonize GPS terminology across standards.
• Software developers and metrology tool vendors - for implementing consistent models of geometrical characteristics and verification operators in CAD/CAM, CAQ and metrology software.
• Quality engineers and process specialists - to align statistical tolerancing and population-based conditions with GPS concepts. Note: ISO 25378:2011 is intended as a roadmap for industry and software makers rather than a direct how‑to for designers.

Related Standards

• ISO 17450‑1:2011 - model for geometrical specification and verification (mathematical basis referenced by ISO 25378).
• ISO/TS 17450‑2 - basic tenets, specifications, operators and uncertainties (operators and duality principle).
• ISO 22432 - description of types of geometrical features used in specification and verification.
• ISO 3534 (parts 1 & 2) - statistical vocabulary referenced for population conditions.

Keywords: ISO 25378:2011, GPS, geometrical product specifications, characteristics and conditions, definitions, geometrical characteristics, operators, duality principle, ISO 17450-1, ISO 22432.