8.11.3.4 IfcDerivedUnit
RV ⓘ
AbV ⓘ
A derived unit is a unit that is formed from an expression of other units.
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IfcUnitAssignment
IfcUnitAssignment
IfcDerivedUnit
IfcDerivedUnit
UnitType: LINEARVELOCITYUNIT
Name: mph
IfcUnitAssignment->IfcDerivedUnit
Units
IfcDerivedUnitElement_0
IfcDerivedUnitElement
Exponent: 1
IfcDerivedUnit->IfcDerivedUnitElement_0
Elements[1]
IfcDerivedUnitElement_1
IfcDerivedUnitElement
Exponent: -1
IfcDerivedUnit->IfcDerivedUnitElement_1
Elements[2]
IfcConversionBasedUnit_0
IfcConversionBasedUnit
UnitType: LENGTHUNIT
Name: mile
IfcDerivedUnitElement_0->IfcConversionBasedUnit_0
Unit
IfcConversionBasedUnit_1
IfcConversionBasedUnit
UnitType: TIMEUNIT
Name: hour
IfcDerivedUnitElement_1->IfcConversionBasedUnit_1
Unit
IfcDimensionalExponents_0
IfcDimensionalExponents
LengthExponent: 1
IfcConversionBasedUnit_0->IfcDimensionalExponents_0
Dimensions
IfcMeasureWithUnit_0
IfcMeasureWithUnit
ValueComponent: 1609
IfcConversionBasedUnit_0->IfcMeasureWithUnit_0
ConversionFactor
IfcSIUnit_0
IfcSIUnit
UnitType: LENGTHUNIT
Name: METRE
IfcMeasureWithUnit_0->IfcSIUnit_0
UnitComponent
IfcDimensionalExponents_1
IfcDimensionalExponents
TimeExponent: 1
IfcConversionBasedUnit_1->IfcDimensionalExponents_1
Dimensions
IfcMeasureWithUnit_1
IfcMeasureWithUnit
ValueComponent: 3600
IfcConversionBasedUnit_1->IfcMeasureWithUnit_1
ConversionFactor
IfcSIUnit_1
IfcSIUnit
UnitType: TIMEUNIT
Name: SECOND
IfcMeasureWithUnit_1->IfcSIUnit_1
UnitComponent
Figure A — An example of how to assign miles per hour as a derived unit { .extDef}
REFERENCE Definition according to ISO/CD 10303-41:1992 of derived_unit.HISTORY New entity in IFC1.5.1.
#
Attribute
Type
Description
IfcDerivedUnit
(5)
1
Elements
SET [1:?] OF IfcDerivedUnitElement
The group of units and their exponents that define the derived unit.
2
UnitType
IfcDerivedUnitEnum
Type of the derived unit chosen from an enumeration of derived unit types for use in IFC models.
EXAMPLE The imperial unit name for a velosity measure is miles per hour, or mph, with a UnitType of .LINEARVELOCITYUNIT.
3
UserDefinedType
OPTIONAL IfcLabel
Type of the derived unit if the UnitType attribute is set to USERDEFINED.
NOTE The UserDefinedType shall only be used if the unit type is not available in UnitType.
4
Name
OPTIONAL IfcLabel
Name of the unit in addition to the unit type, particularly when the derived unit elements refer to conversion or context based units.
EXAMPLE The imperial unit name for a velocity measure is miles per hour, or MPH, with a Name of 'MPH'.
*
Dimensions
IfcDimensionalExponents
This attribute is formally derived.
IfcDeriveDimensionalExponents ( Elements ) Dimensional exponents derived using the function IfcDeriveDimensionalExponents using (SELF) as the input value.
Table B
Name
Description
WR1
Units as such shall not be re-defined as derived units.
( SIZEOF ( Elements ) > 1 ) OR ( ( SIZEOF ( Elements ) = 1 ) AND ( Elements [ 1 ] . Exponent <> 1 ) )
WR2
When attribute UnitType has enumeration value USERDEFINED
then attribute UserDefinedType shall also have a value.
( UnitType <> IfcDerivedUnitEnum . USERDEFINED ) OR
( ( UnitType = IfcDerivedUnitEnum . USERDEFINED ) AND
( EXISTS ( SELF . UserDefinedType ) ) )
Table C ENTITY IfcDerivedUnit ;
Elements : SET [ 1 : ? ] OF IfcDerivedUnitElement ;
UnitType : IfcDerivedUnitEnum ;
UserDefinedType : OPTIONAL IfcLabel ;
Name : OPTIONAL IfcLabel ;
DERIVE
Dimensions : IfcDimensionalExponents := IfcDeriveDimensionalExponents ( Elements ) ;
WHERE
WR1 : ( SIZEOF ( Elements ) > 1 ) OR ( ( SIZEOF ( Elements ) = 1 ) AND ( Elements [ 1 ] . Exponent <> 1 ) ) ;
WR2 : ( UnitType <> IfcDerivedUnitEnum . USERDEFINED ) OR
( ( UnitType = IfcDerivedUnitEnum . USERDEFINED ) AND
( EXISTS ( SELF . UserDefinedType ) ) ) ;
END_ENTITY ;
