Building Definition Language

A Datum is a theoretically exact reference derived from a physical or virtual feature and used to establish position, orientation, measurement, or assembly control.

Datum types may include:

datum point;

datum axis;

datum line;

datum plane;

datum surface;

datum coordinate system;

datum target.

Every Datum shall define:

Datum ID;

source feature;

datum type;

coordinate system;

purpose;

accessibility;

inspection method;

priority;

applicable tolerance.

A datum hierarchy may include:

primary datum;

secondary datum;

tertiary datum.

Example:

datum Node_Face_Datum_System {

primary: @Node_Face_Seating_Plane;

secondary: @Node_Face_Vertical_Key;

tertiary: @Node_Face_Lateral_Pin;

}

The primary datum establishes the principal seating condition. Secondary and tertiary datums constrain the remaining degrees of freedom.

Interface datums shall remain linked to physical features suitable for manufacturing, assembly, inspection, and robotic localization.

Decorative finishes, flexible covers, or movable surfaces shall not serve as critical datums unless specifically engineered for that purpose.

A reference plane may define:

structural center plane;

finished surface;

Interface face;

assembly plane;

cutting plane;

inspection plane;