An IfcConversionBasedUnit is used to define a unit that has a conversion rate to a base unit. To identify some commonly used conversion based units, the standard designations (case insensitive) for the Name attribute are indicated in Table 1.
Table 1 — Standard unit names
EXAMPLE An inch is a converted unit. It is from the Imperial system, its name is "inch" and it can be related to the SI unit, millimetre, through a measure with unit whose value is 25.4 millimetre. A foot is also a converted unit. It is from the Imperial system, its name is "foot" and it can be related to an IfcSIUnit, millimetre, either directly or through the unit called "inch". Note that several US customary units differ from Imperial units (nonmetric English units) of the same name.
NOTE Definition according to ISO/CD 10303-41:1992
A conversion based unit is a unit that is defined based on a measure with unit.
NOTE Entity adapted from conversion_based_unit defined in ISO 10303-41.
HISTORY New entity in IFC1.5.1.
IFC2x3 CHANGE Standard names of typical units added.
IFC4 CHANGE Further names added: square inch, square foot, square mile, square yard, cubic inch, cubic foot, cubic yard, fluid ounce UK/US, ton UK/US, degree.
|1||Dimensions||IfcDimensionalExponents||The dimensional exponents of the SI base units by which the named unit is defined.|
|2||UnitType||IfcUnitEnum||The type of the unit.|
|3||Name||IfcLabel||The word, or group of words, by which the conversion based unit is referred to.|
|4||ConversionFactor||IfcMeasureWithUnit||The physical quantity from which the converted unit is derived.|
|HasExternalReference||SET [0:?] OF IfcExternalReferenceRelationship FOR RelatedResourceObjects||Reference to external information, e.g. library, classification, or document information, which is associated with the conversion-based unit.|
> IFC4 CHANGE New inverse attribute.
ENTITY IfcConversionBasedUnit SUPERTYPE OF (ONEOF (IfcConversionBasedUnitWithOffset)) SUBTYPE OF (IfcNamedUnit); Name : IfcLabel; ConversionFactor : IfcMeasureWithUnit; INVERSE HasExternalReference : SET [0:?] OF IfcExternalReferenceRelationship FOR RelatedResourceObjects; END_ENTITY;