8.11 IfcMeasureResource

8.11.1 Schema Definition

The IfcMeasureResource schema specifies units and defined measure types that may be assigned to quantities.

NOTE  The fundamental unit types used in this schema are based on the SI system defined in ISO 1000+A1, 1992, 1998. Units in measurement systems other than SI may be derived using this schema. Many definitions declared in the IfcMeasureResource schema is adapted from ISO 10303-41
NOTE  In the definitions of the unit exponents the use of superscript font has been omitted. Therefore, m2 means square metre, m3 means cubic meter.

In different types of units there are five basic cases:

With regard to the usage of the measure defined types (for example, IfcLengthMeasure, IfcTimeMeasure) as attribute datatypes in this specification, there are three basic cases:

  1. The datatype of an attribute of an entity type is a measure defined type as such without possibility on an instance level to define the unit of the measure value:
    ENTITY IfcBoundingBox
    SUBTYPE OF(IfcGeometricRepresentationItem);
    Corner : IfcCartesianPoint;
    XDim : IfcPositiveLengthMeasure;
    YDim : IfcPositiveLengthMeasure;
    ZDim : IfcPositiveLengthMeasure;
    END_ENTITY;
    In this case, it is the global unit assignment for the corresponding unit for the measure type that defines the unit for all the usages of this defined measure type (except for cases 2 and 3 below).
  2. The datatype of an attribute is IfcMeasureWithUnit, which allows for definition of unit per instance of that entity type, independent and possibly overriding the global unit assignment:
    ENTITY IfcConversionBasedUnit
    SUPERTYPE OF (ONEOF
    (IfcConversionBasedUnitWithOffset))
    SUBTYPE OF (IfcNamedUnit);
    Name : IfcLabel;
    ConversionFactor : IfcMeasureWithUnit;
    END_ENTITY;
    In this case the relevant measure defined type (from the IfcMeasureWithUnit.ValueComponent : IfcValue select list) is not exactly defined by the schema, but implied by the context.
  3. The entity type has a separate "unit" attribute which allows for defining the unit for another attribute of the entity type for representing the actual value:
    ENTITY IfcPropertySingleValue
    SUBTYPE OF (IfcSimpleProperty);
    NominalValue : IfcValue;
    Unit : OPTIONAL IfcUnit;
    END_ENTITY;

Although in the cases 2 and 3 different units could be used for different instances of the same entity type or for the same measure type in attributes of different entity types, it is recommended not to mix different units for same measure defined types, if it can be avoided. Below some examples of each of the above basic cases are given.

NOTE  In the example instantiations in the form of IFC data exchange files, mainly the measure and unit -relevant attributes are given the values; the other attributes are given no values (in the form of $-sign) independent of whether they should actually have values because of being nonoptional attributes.

Table 684 indicates measures, units, and corresponding data types.

MeasureTypeUnitSymbolDerivationIfcSiUnitEnumIfcUnitEnumIfcDerivedUnitEnumDefined value types
Absorbed dose, specific energy
impact, kerma, absorbed dose index
SI / DerivedgrayGyJ / kgGRAYABSORBEDDOSEUNITIfcAbsorbedDoseMeasure
AccelerationDerivedm / s2ACCELERATIONUNITIfcAccelerationMeasure
Acidity (pH)DerivedpHpHmol / lPHUNITIfcPHMeasure
Activity (of radionuclide)SI / DerivedbecquerelBq1 / sBECQUERELRADIOACTIVITYUNITIfcRadioActivityMeasure
Amount of substanceSI/BasicmolemolMOLEAMOUNTOFSUBSTANCEUNITIfcAmountOfSubstanceMeasure
Angular velocityDerivedrad / sANGULARVELOCITYUNITIfcAngularVelocityMeasure
AreaSI/Derivedsquare metrem2m2SQUARE_METREAREAUNITIfcAreaMeasure
Area densityDerivedkg / m2AREADENSITYUNITIfcAreaDensityMeasure
-IfcBoolean
-IfcComplexNumber
Compound plane angleCompounddegree, min, sCOMPOUNDPLANEANGLEUNITIfcCompoundPlaneAngleMeasure
-IfcContextDependentMeasure
-IfcCountMeasure
-IfcDescriptiveMeasure
CapacitanceSI / DerivedfaradFC / VFARADELECTRICCAPACITANCEUNITIfcElectricCapacitanceMeasure
Celsius temperatureSI / Basicdegree CelsiusºC1 ºC = 1 KDEGREE_CELSIUSTHERMODYNAMICTEMPERATUREUNITIfcThermodynamicTemperatureMeasure
CurvatueDerivedrad / mCURVATUREUNITIfcCurvatureMeasure
-IfcDate
(lexical representation according to ISO 8601)
-IfcDateTime
(lexical representation according to ISO 8601)
Dose equivalent, dose equivalent
index
SI / DerivedsievertSvJ / kgSIEVERTDOSEEQUIVALENTUNITIfcDoseEquivalentMeasure
-IfcDuration
(lexical representation according to ISO 8601)
Dynamic viscosityDerivedPa · sDYNAMICVISCOSITYUNITIfcDynamicViscosityMeasure
Electric charge,
quantity of electricity
SI / DerivedcoulombCA · sCOULOMBELECTRICCHARGEUNITIfcElectricChargeMeasure
Electric conductanceSI / DerivedsiemensS1 / WSIEMENSELECTRICCONDUCTANCEUNITIfcElectricConductanceMeasure
Electric current SI / BasicampereAAMPEREELECTRICCURRENTUNITIfcElectricCurrentMeasure
Electric potential, potential
difference, tension, electromotive force
SI / DerivedvoltVW / AVOLTELECTRICVOLTAGEUNITIfcElectricVoltageMeasure
Electric resistanceSI / DerivedohmWV / AOHMELECTRICRESISTANCEUNITIfcElectricResistanceMeasure
Energy, work, quantity of heatSI / DerivedjouleJN · mJOULEENERGYUNITIfcEnergyMeasure
ForceSI / DerivednewtonNkg · m / s2NEWTONFORCEUNITIfcForceMeasure
FrequencySI / DerivedhertzHz1 / sHERTZFREQUENCYUNITIfcFrequencyMeasure
Heat flux densityDerivedW / m2HEATFLUXDENSITYUNITIfcHeatFluxDensityMeasure
Heating valueDerivedJ / kgHEATINGVALUEUNITIfcHeatingValueMeasure
-IfcIdentifier
IlluminanceSI / Derivedluxlxlm / m2LUXILLUMINANCEUNITIfcIlluminanceMeasure
InductanceSI / DerivedhenryHWb / AHENRYINDUCTANCEUNITIfcInductanceMeasure
-IfcInteger
(Integer) Count rateDerived1 / sINTEGERCOUNTRATEUNITIfcIntegerCountRateMeasure
Ion concentrationDerivedg / lIONCONCENTRATIONUNITIfcIonConcentrationMeasure
Isothermal moisture capacityDerivedm3 / kgISOTHERMALMOISTURECAPACITYUNITIfcIsothermalMoistureCapacityMeasure
Kinematic viscosityDerivedm2 / sKINEMATICVISCOSITYUNITIfcKinematicViscosityMeasure
LengthSI / BasicmetremMETRELENGTHUNITIfcLengthMeasure
-IfcLabel
Linear forceDerivedN / mLINEARFORCEUNITIfcLinearForceMeasure
Linear momentDerivedN · m / mLINEARMOMENTUNITIfcLinearMomentMeasure
Linear stiffnessDerivedN / mLINEARSTIFFNESSUNITIfcLinearStiffnessMeasure
Linear velocityDerivedm / sLINEARVELOCITYUNITIfcLinearVelocityMeasure
-IfcLogical
Luminous fluxSI / Derivedlumenlmcd · srLUMENLUMINOUSFLUXUNITIfcLuminousFluxMeasure
Luminous intensitySI / BasiccandelacdCANDELALUMINOUSINTENSITYUNITIfcLuminousIntensityMeasure
Luminous intensity distributionDerivedcd / lmLUMINOUSINTENSITYDISTRIBUTIONUNITIfcLuminousIntensityDistributionMeasure
Magnetic fluxSI / DerivedweberWbV · sWEBERMAGNETICFLUXUNITIfcMagneticFluxMeasure
Magnetic flux densitySI / DerivedteslaTWb / m2TESLAMAGNETICFLUXDENSITYUNITIfcMagneticFluxDensityMeasure
MassSI / Basicgramg (kg)GRAMMASSUNITIfcMassMeasure
Mass densityDerivedkg / m3MASSDENSITYUNITIfcMassDensityMeasure
Mass flow rateDerivedkg / sMASSFLOWRATEUNITIfcMassFlowRateMeasure
Mass per lengthDerivedkg / mMASSPERLENGTHUNITIfcMassPerLengthMeasure
Modulus of elasticityDerivedN / m2MODULUSOFELASTICITYUNITIfcModulusOfElasticityMeasure
Modulus of linear subgrade reactionDerivedN / m2MODULUSOFLINEARSUBGRADEREACTIONUNITIfcModulusOfLinearSubgradeReactionMeasure
Modulus of rotational subgrade reactionDerivedN · m / m · radMODULUSOFROTATIONALSUBGRADEREACTIONUNITIfcModulusOfRotationalSubgradeReactionMeasure
Modulus of subgrade reactionDerivedN / m3MODULUSOFSUBGRADEREACTIONUNITIfcModulusOfSubgradeReactionMeasure
Moisture diffusivityDerivedm3 / sMOISTUREDIFFUSIVITYUNITIfcMoistureDiffusivityMeasure
Molecular weightDerivedg / molMOLECULARWEIGHTUNITIfcMolecularWeightMeasure
Moment of inertiaDerivedm4MOMENTOFINERTIAUNITIfcMomentOfInertiaMeasure
-IfcMonetaryMeasure
(Non negative length)mLENGTHUNITIfcNonNegativeLengthMeasure
-IfcNormalisedRatioMeasure
-IfcNumericMeasure
-IfcParameterValue
Planar forceDerivedN / m2PLANARFORCEUNITIfcPlanarForceMeasure
Plane angleSI / Derivedradianradm / m = 1RADIANPLANEANGLEUNITIfcPlaneAngleMeasure
(Positive length)mLENGTHUNITIfcPositiveLengthMeasure
(Positive plane angle)radPLANEANGLEUNITIfcPositivePlaneAngleMeasure
-IfcPositiveRatioMeasure
PowerSI / DerivedwattWJ / sWATTPOWERUNITIfcPowerMeasure
Pressure, stressSI / DerivedpascalPaN / m2PASCALPRESSUREUNITIfcPressureMeasure
- IfcRatioMeasure
- IfcReal
Rotational frequencyDerivedcycles / sROTATIONALFREQUENCYUNITIfcRotationalFrequencyMeasure
Rotational massDerivedkg · m2ROTATIONALMASSUNITIfcRotationalMassMeasure
Rotational stiffnessDerivedN · m / radROTATIONALSTIFFNESSUNITIfcRotationalStiffnessMeasure
Sectional area integralDerivedm5SECTIONALAREAINTEGRALUNITIfcSectionalAreaIntegralMeasure
Section modulusDerivedm3SECTIONMODULUSUNITIfcSectionModulusMeasure
Shear modulusDerivedN / m2SHEARMODULUSUNITIfcShearModulusMeasure
Solid angleSI / Derivedsteradinsrm2 / m2 = 1STERADIANSOLIDANGLEUNITIfcSolidAngleMeasure
Sound powerwattWWSOUNDPOWERUNITIfcSoundPowerMeasure
Sound power leveldecibeldbW / WSOUNDPOWERLEVELUNITIfcSoundPowerLevelMeasure
Sound pressurepascalPaPaSOUNDPRESSUREUNITIfcSoundPressureMeasure
Sound pressure leveldecibeldbPa / PaSOUNDPRESSURELEVELUNITIfcSoundPressureLevelMeasure
Specific heat capacityDerivedJ / kg· KSPECIFICHEATCAPACITYUNITIfcSpecificHeatCapacityMeasure
Temperature gradientK / mTEMPERATUREGRADIENTUNITIfcTemperatureGradientMeasure
Temperature changeK / sTEMPERATURERATEOFCHANGEUNITIfcTemperatureRateOfChangeMeasure
-IfcText
Thermal admittanceDerivedW / m2 · KTHERMALADMITTANCEUNITIfcThermalAdmittanceMeasure
Thermal conductivityDerivedW / m · KTHERMALCONDUCTIVITYUNITIfcThermalConductivityMeasure
Thermal expansion coefficient1 / KTHERMALEXPANSIONCOEFFICIENTUNITIfcThermalExpansionCoefficientMeasure
Thermal resistanceDerivedm2 · K / WTHERMALRESISTANCEUNITIfcThermalResistanceMeasure
Thermal transmittanceDerivedW / m2 · KTHERMALTRANSMITTANCEUNITIfcThermalTransmittanceMeasure
Thermodynamic temperatureSI / BasickelvinKKELVINTHERMODYNAMICTEMPERATUREUNITIfcThermodynamicTemperatureMeasure
-IfcTime
(lexical representation according to ISO 8601)
TimeSI / BasicsecondsSECONDTIMEUNITIfcTimeMeasure
-IfcTimeStamp
TorqueDerivedN· mTORQUEUNITIfcTorqueMeasure
Vapor permeabilityDerivedkg / s · m · PaVAPORPERMEABILITYUNITIfcVaporPermeabilityMeasure
VolumeSI / Derivedcubic metrem3m3CUBIC_METREVOLUMEUNITIfcVolumeMeasure
Volumetric flow rateDerivedm3 / sVOLUMETRICFLOWRATEUNITIfcVolumetricFlowRateMeasure
Warping constantm6WARPINGCONSTANTUNITIfcWarpingConstantMeasure
Warping momentDerivedN · m2WARPINGMOMENTUNITIfcWarpingMomentMeasure

Table 684 — Measures and units

Link to EXPRESS-G diagram EXPRESS-G diagram