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3D Dimensional Measurement

Definition

complete three-dimensional geometry capture with tolerance comparison and form analysis via CT

Synonyms:
3D MetrologyDimensional CT MeasurementCT Coordinate Measurement

What is 3D Dimensional Measurement?

3D dimensional measurement refers to the complete three-dimensional capture of a part’s geometry together with the subsequent comparison against nominal specifications (CAD model, drawing tolerance). Using industrial CT, the complete internal and external volume of a part is digitised in a single measurement — without disassembly and without mechanical access to hidden surfaces.

Scientific background

The basis is the extraction of surface points from the CT volume dataset using grey-value threshold determination. The resulting point cloud is transferred into a coordinate measurement system and aligned against the CAD reference model (best-fit or datum-feature alignment per ISO 5459). Measurement deviations are displayed as a colour map.

Relevant key metrics

  • Measurement uncertainty U (k=2) per VDI/VDE 2630 Part 2.1 must be less than 1/3 of the tolerance to be tested.
  • Voxel size defines the theoretical resolution limit; practical measurement uncertainty typically lies 3–5× above the voxel size.
  • Reproducibility is ensured by repeat measurements and Gauss/Chebyshev fitting.

Standards and thresholds

  • Standards: VDI/VDE 2630 Part 1.2:2018 and Part 2.1:2015 (CT metrology), ISO 10360-8 (CT-CMM), ISO 14253 (conformity decision).
  • Typical thresholds: Measurement uncertainty ≤ 1/3 of the drawing tolerance (commonly applied criterion); for tight tolerances (< 50 µm) micro-CT systems are required.
  • Validity: Release must always be qualified per material, geometry and tolerance class; temperature normalisation (20 °C) must be observed.

Application in industrial practice

  • First-article inspection and EMPB documentation for automotive and aerospace.
  • Dimensioning of undercuts, internal bores and cavities without destroying the part.
  • Complete form analysis on additively manufactured parts (AM).

Sources and reference date

  • VDI/VDE 2630 Part 1.2:2018-06 and Part 2.1:2015-06.
  • ISO 10360-8:2021.
  • ISO 14253-1:2018.
  • Reference date: March 2026.