Overview
ISO 18183-3:2024 is part of the ISO series on Geometrical Product Specifications (GPS) and defines the methods used for specification and verification of the partition operation within GPS. The standard specifies how to partition the skin model (specification), the nominal model, and the sampled surface model (verification) into meaningful geometric features (single surfaces or single lines). It explicitly excludes profile and areal surface texture.
Key topics and technical requirements
- Default partition
- The default behaviour partitions models into single features (single surfaces or single lines) of maximum extent.
- A single surface is a connected surface of maximum area where subsets do not violate the partial ordering of invariance classes; for revolute surfaces the generatrix must be a single line.
- A single line is a connected, finite line of greatest possible length consistent with invariance class ordering.
- Invariance classes and partial ordering
- The standard uses a hierarchy of invariance classes (degree of invariance) to determine allowable partitions.
- Use of curvature and slippable motion
- For real (discrete or sampled) geometry, curvature analysis and concepts like slippable motion guide the detection of single surfaces and lines.
- Explicit partition
- Covers cases where partitions are defined beyond the default (e.g., united features, restricted single features, restricted compound features); all explicit partitions start from the default partition.
- Informative annexes
- Annex A: methods and concepts for discrete curvature (fitting and discrete methods, Laplace–Beltrami discretization, classification of local shape)
- Annex B: implementation approaches for default partition on meshes/point clouds (classification of partitioning methods)
- Annex C: relationship to the GPS matrix model
Practical applications and who uses it
- Metrology and inspection teams applying model-based verification to determine which portions of a surface/line to treat as a single feature.
- Quality engineers and manufacturers specifying tolerances and inspection strategies for parts with multiple geometric features (e.g., turned/revolved parts, complex surfaces).
- CAD/CAM and inspection software developers implementing partition algorithms for sampled surfaces and skin models (point clouds, meshes).
- Standards committees and system integrators aligning GPS specifications across design, manufacturing and verification workflows.
Related standards
For implementation or procurement, consult the full ISO 18183-3:2024 text from ISO for normative definitions, examples and normative clauses.