What is CAD Nominal/Actual Comparison?
CAD nominal/actual comparison refers to the geometric comparison of CT actual data against nominal CAD data. The method delivers actionable quality data for product release, process optimisation and root-cause analysis.
Scientific background
Methodologically, the procedure relies on standardised workflows covering data acquisition, segmentation, feature extraction and evaluation. Core elements include registration, surface determination and deviation mapping. Meaningful results only emerge from traceable criteria and defined acceptance limits.
Relevant key metrics
- Detection limit and misclassification risk for the relevant failure modes.
- Repeatability of the evaluation for identical input data.
- Relationship between indicators and functional load zones / specifications.
Standards and thresholds
- Standards: ISO 1101:2017, ISO 5459:2024, ISO 14405-1:2025 as well as VDI/VDE 2630 Part 1.2:2018-06.
- Typical thresholds (in practice): Surface or point deviation within drawing tolerance (e.g. ±0.10 mm); critical features 100 % within specification.
- Validity: Drawing, datum system and customer-specific inspection plan are decisive.
Application in industrial practice
- Data-based release decisions during ramp-up and series production.
- Early detection of deviations with cause-oriented prioritisation.
- Improved customer and supplier communication through objective CT reports.
Sources and reference date
- ISO 1101:2017 (GPS — Geometrical tolerancing).
- ISO 5459:2024 (Datums and datum systems).
- ISO 14405-1:2025 (Dimensional tolerancing — Linear sizes).
- VDI/VDE 2630 Part 1.2:2018-06 (CT in dimensional measurement).
- Reference date: February 2026.