Engineering glossary

Geometric dimensioning and tolerancing describes allowed variation in form, orientation, location and related geometric requirements. Interpretation depends on the governing standard, its edition and the complete specification.

Product and manufacturing information includes dimensions, tolerances, notes and other requirements associated with product geometry. An exchange file can contain only part of the information present in the authoring system.

A datum is a theoretically exact reference used to establish the location or orientation of a tolerance requirement. The physical datum feature and the derived datum are different concepts.

A datum reference frame establishes the reference system for interpreting specified geometric controls. Reordering referenced datums can change the meaning of the requirement.

Model-based definition uses a model and its associated product information to communicate design requirements. A shape-only export may not preserve the complete definition.

An application protocol in the STEP family for managed model-based 3D engineering exchange. The information transferred depends on protocol edition, exporter settings and implementation.

The aerospace first article inspection standard defines requirements for documenting verification of a representative production article. The contract determines the applicable edition and additional customer requirements.

First article inspection provides documented verification of the production process against the applicable design requirements. It involves evidence beyond a nominal CAD comparison.

A practical term used here for reviewing the inspection impact of a change against a previous baseline. Formal partial-FAI obligations are determined by the applicable standard and customer requirements.

Production Part Approval Process is a structured customer approval process used in automotive supply chains. A dimensional report is one possible element of the submission, not the complete process.

Quality Information Framework is an XML-based standard for exchanging connected quality and metrology information. Schema-valid data still needs engineering interpretation and application compatibility checks.

Dimensional Measuring Interface Standard is used to describe dimensional measurement information and operations. Support for a format does not guarantee that a generated program is safe for a specific machine.

A coordinate measuring machine collects spatial measurements to evaluate part characteristics. Its measurement strategy and uncertainty affect the interpretation of the result.

Long-Term Archiving and Retrieval concerns preserving usable technical product information over time. It includes process and evidence requirements beyond storing a neutral CAD file.

Machine-readable meaning associated with product annotations. It allows downstream software to distinguish a structured requirement from a collection of displayed lines and text.

The visual presentation of product annotations. A readable annotation does not by itself establish that its meaning is available as structured data.

Boundary representation describes a solid or surface through geometric boundaries and their topology. Display tessellation is generated from this representation for viewing.

A polygonal approximation of a surface used for display or mesh workflows. Its resolution affects what can be seen and which geometric details are represented.

An identified version of design data within a controlled change process. A renamed file is not necessarily a new geometric revision.

A requirement selected for verification, such as a dimension, geometric control or drawing note. Each characteristic needs an unambiguous relationship to its source.

Assigning visible identifiers to inspection characteristics so a reviewer can connect the model or drawing with the inspection list.

A visual encoding of differences between compared geometries. The colour range and sampling method are essential to interpreting it.

Declared quantities or reference information used to help assess a model transfer. Agreement in a few aggregate values cannot establish complete geometric equivalence.

A result state indicating that a stated check has no completed evaluation in the reported scope. It is neither a successful check nor necessarily a defect in the part.