IFC 4.3.x development

8.11.3.3 IfcConversionBasedUnitWithOffset

Change log

IFC4

added

8.11.3.3.1 Semantic definitions at the entity

IfcConversionBasedUnitWithOffset is a unit which is converted from another unit by applying a conversion factor and an offset.

HISTORY  New entity in IFC4.

Example: The temperature unit Fahrenheit is based on the temperature unit Kelvin as follows:

f = k · 1.8 – 459.67

wherein k is an absolute temperature expressed in Kelvin and f is the same temperature in Fahrenheit. The following entity instances provide Fahrenheit as a unit:

```

IfcConversionBasedUnitWithOffset(
    IfcDimensionalExponents(0, 0, 0, 0, 1, 0, 0),
    THERMODYNAMICTEMPERATUREUNIT,
    'Fahrenheit',
    IfcMeasureWithUnit(
        IfcThermodynamicTemperatureMeasure(1.8),
        IfcSIUnit(THERMODYNAMICTEMPERATUREUNIT, ?, KELVIN)),
    -459.67);

```

8.11.3.3.1 Attributes

# Attribute Type Description
IfcNamedUnit
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.
IfcConversionBasedUnit
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.
HasExternalReferenceSET [0:?] OF IfcExternalReferenceRelationship FOR RelatedResourceObjectsReference to external information, e.g. library, classification, or document information, which is associated with the conversion-based unit.

> IFC4 CHANGE New inverse attribute.
IfcConversionBasedUnitWithOffset
5 ConversionOffset IfcReal A positive or negative offset to add after the inherited ConversionFactor was applied.

8.11.3.3.2 Entity inheritance

dot_inheritance IfcConversionBasedUnitWithOffset IfcConversionBasedUnitWithOffset IfcConversionBasedUnit IfcConversionBasedUnit IfcConversionBasedUnitWithOffset->IfcConversionBasedUnit IfcNamedUnit IfcNamedUnit IfcConversionBasedUnit->IfcNamedUnit IfcContextDependentUnit IfcContextDependentUnit IfcContextDependentUnit->IfcNamedUnit IfcSIUnit IfcSIUnit IfcSIUnit->IfcNamedUnit

8.11.3.3.3 Formal representations

ENTITY IfcConversionBasedUnitWithOffset
 SUBTYPE OF (IfcConversionBasedUnit);
	ConversionOffset : IfcReal;
END_ENTITY;