IFC (IFC4X3_ADD2) under development

8.11 IfcMeasureResource

8.11.1 Schema definition

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

In different types of units there are five basic cases:

  • Basic SI-units, which cover a number of fundamental units of mainly physical quantities defined by ISO-1000{ .int-ref} such as meter or millimeter as unit for length measure or square meter as a unit for area measure. The unit may have a scaling prefix (for example: milli, kilo).
  • Derived SI-units, which are defined as a derivation of the basic SI-units, for example, Newton (kg m / s2) as a unit of force. Both basic and derived SI-units are in the IFCs represented by IfcSIUnit.
  • Conversion based units, which can be derived from SI-units by a scaling factor; e.g. inch which can be defined using SI-unit for length measure, i.e. an inch is 25.4 millimeters.
  • Derived units, which can be defined as a derivation or combination of a number of basic units. In a derived unit each of the basic unit "component" has a dimensional exponent in defining the derived unit; e.g. kg / m2, where kilogram (kg) has dimensional exponent 1 and meter (m) has exponent -2.
  • Context dependent units, which cannot be defined as conversion based unit using SI-units.

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:

First, 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;

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).

Second, 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
 SUBTYPE OF (IfcNamedUnit);
  Name : IfcLabel;
  ConversionFactor : IfcMeasureWithUnit;

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.

Third, 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;

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.

Table 8.11.A indicates measures, units, and corresponding data types.

Measure Type Unit Symbol Derivation IfcSIUnitEnum IfcUnitEnum IfcDerivedUnitEnum Defined value types
Absorbed dose, specific energyimpact, kerma, absorbed dose index SI / Derived gray Gy J / kg GRAY ABSORBEDDOSEUNIT IfcAbsorbedDoseMeasure
Acceleration Derived m / s2 ACCELERATIONUNIT IfcAccelerationMeasure
Acidity (pH) Derived pH pH mol / l PHUNIT IfcPHMeasure
Activity (of radionuclide) SI / Derived becquerel Bq 1 / s BECQUEREL RADIOACTIVITYUNIT IfcRadioActivityMeasure
Amount of substance SI/Basic mole mol MOLE AMOUNTOFSUBSTANCEUNIT IfcAmountOfSubstanceMeasure
Angular velocity Derived rad / s ANGULARVELOCITYUNIT IfcAngularVelocityMeasure
Area SI/Derived square metre m2 m2 SQUARE_METRE AREAUNIT IfcAreaMeasure
Area density Derived kg / m2 AREADENSITYUNIT IfcAreaDensityMeasure
- IfcBoolean
- IfcComplexNumber
Compound plane angle Compound degree, min, s COMPOUNDPLANEANGLEUNIT IfcCompoundPlaneAngleMeasure
- IfcContextDependentMeasure
- IfcCountMeasure
- IfcDescriptiveMeasure
Capacitance SI / Derived farad F C / V FARAD ELECTRICCAPACITANCEUNIT IfcElectricCapacitanceMeasure
Celsius temperature SI / Basic degree Celsius ºC 1 ºC = 1 K DEGREE_CELSIUS THERMODYNAMICTEMPERATUREUNIT IfcThermodynamicTemperatureMeasure
Curvatue Derived rad / m CURVATUREUNIT IfcCurvatureMeasure
- IfcDate (lexical representation according to ISO 8601)
- IfcDateTime (lexical representation according to ISO 8601)
Dose equivalent, dose equivalent index SI / Derived sievert Sv J / kg SIEVERT DOSEEQUIVALENTUNIT IfcDoseEquivalentMeasure
- IfcDuration (lexical representation according to ISO 8601)
Dynamic viscosity Derived Pa · s DYNAMICVISCOSITYUNIT IfcDynamicViscosityMeasure
Electric charge, quantity of electricity SI / Derived coulomb C A · s COULOMB ELECTRICCHARGEUNIT IfcElectricChargeMeasure
Electric conductance SI / Derived siemens S 1 / W SIEMENS ELECTRICCONDUCTANCEUNIT IfcElectricConductanceMeasure
Electric current SI / Basic ampere A AMPERE ELECTRICCURRENTUNIT IfcElectricCurrentMeasure
Electric potential, potential difference, tension, electromotive force SI / Derived volt V W / A VOLT ELECTRICVOLTAGEUNIT IfcElectricVoltageMeasure
Electric resistance SI / Derived ohm W V / A OHM ELECTRICRESISTANCEUNIT IfcElectricResistanceMeasure
Energy, work, quantity of heat SI / Derived joule J N · m JOULE ENERGYUNIT IfcEnergyMeasure
Force SI / Derived newton N kg · m / s2 NEWTON FORCEUNIT IfcForceMeasure
Frequency SI / Derived hertz Hz 1 / s HERTZ FREQUENCYUNIT IfcFrequencyMeasure
Heat flux density Derived W / m2 HEATFLUXDENSITYUNIT IfcHeatFluxDensityMeasure
Heating value Derived J / kg HEATINGVALUEUNIT IfcHeatingValueMeasure
- IfcIdentifier
Illuminance SI / Derived lux lx lm / m2 LUX ILLUMINANCEUNIT IfcIlluminanceMeasure
Inductance SI / Derived henry H Wb / A HENRY INDUCTANCEUNIT IfcInductanceMeasure
- IfcInteger
(Integer) Count rate Derived 1 / s INTEGERCOUNTRATEUNIT IfcIntegerCountRateMeasure
Ion concentration Derived g / l IONCONCENTRATIONUNIT IfcIonConcentrationMeasure
Isothermal moisture capacity Derived m3 / kg ISOTHERMALMOISTURECAPACITYUNIT IfcIsothermalMoistureCapacityMeasure
Kinematic viscosity Derived m2 / s KINEMATICVISCOSITYUNIT IfcKinematicViscosityMeasure
Length SI / Basic metre m METRE LENGTHUNIT IfcLengthMeasure
- IfcLabel
Linear force Derived N / m LINEARFORCEUNIT IfcLinearForceMeasure
Linear moment Derived N · m / m LINEARMOMENTUNIT IfcLinearMomentMeasure
Linear stiffness Derived N / m LINEARSTIFFNESSUNIT IfcLinearStiffnessMeasure
Linear velocity Derived m / s LINEARVELOCITYUNIT IfcLinearVelocityMeasure
- IfcLogical
Luminous flux SI / Derived lumen lm cd · sr LUMEN LUMINOUSFLUXUNIT IfcLuminousFluxMeasure
Luminous intensity SI / Basic candela cd CANDELA LUMINOUSINTENSITYUNIT IfcLuminousIntensityMeasure
Luminous intensity distribution Derived cd / lm LUMINOUSINTENSITYDISTRIBUTIONUNIT IfcLuminousIntensityDistributionMeasure
Magnetic flux SI / Derived weber Wb V · s WEBER MAGNETICFLUXUNIT IfcMagneticFluxMeasure
Magnetic flux density SI / Derived tesla T Wb / m2 TESLA MAGNETICFLUXDENSITYUNIT IfcMagneticFluxDensityMeasure
Mass SI / Basic gram g (kg) GRAM MASSUNIT IfcMassMeasure
Mass density Derived kg / m3 MASSDENSITYUNIT IfcMassDensityMeasure
Mass flow rate Derived kg / s MASSFLOWRATEUNIT IfcMassFlowRateMeasure
Mass per length Derived kg / m MASSPERLENGTHUNIT IfcMassPerLengthMeasure
Modulus of elasticity Derived N / m2 MODULUSOFELASTICITYUNIT IfcModulusOfElasticityMeasure
Modulus of linear subgrade reaction Derived N / m2 MODULUSOFLINEARSUBGRADEREACTIONUNIT IfcModulusOfLinearSubgradeReactionMeasure
Modulus of rotational subgrade reaction Derived N · m / m · rad MODULUSOFROTATIONALSUBGRADEREACTIONUNIT IfcModulusOfRotationalSubgradeReactionMeasure
Modulus of subgrade reaction Derived N / m3 MODULUSOFSUBGRADEREACTIONUNIT IfcModulusOfSubgradeReactionMeasure
Moisture diffusivity Derived m3 / s MOISTUREDIFFUSIVITYUNIT IfcMoistureDiffusivityMeasure
Molecular weight Derived g / mol MOLECULARWEIGHTUNIT IfcMolecularWeightMeasure
Moment of inertia Derived m4 MOMENTOFINERTIAUNIT IfcMomentOfInertiaMeasure
- IfcMonetaryMeasure
(Non negative length) m LENGTHUNIT IfcNonNegativeLengthMeasure
- IfcNormalisedRatioMeasure
- IfcNumericMeasure
- IfcParameterValue
Planar force Derived N / m2 PLANARFORCEUNIT IfcPlanarForceMeasure
Plane angle SI / Derived radian rad m / m = 1 RADIAN PLANEANGLEUNIT IfcPlaneAngleMeasure
(Positive length) m LENGTHUNIT IfcPositiveLengthMeasure
(Positive plane angle) rad PLANEANGLEUNIT IfcPositivePlaneAngleMeasure
- IfcPositiveRatioMeasure
Power SI / Derived watt W J / s WATT POWERUNIT IfcPowerMeasure
Pressure, stress SI / Derived pascal Pa N / m2 PASCAL PRESSUREUNIT IfcPressureMeasure
- IfcRatioMeasure
- IfcReal
Rotational frequency Derived cycles / s ROTATIONALFREQUENCYUNIT IfcRotationalFrequencyMeasure
Rotational mass Derived kg · m2 ROTATIONALMASSUNIT IfcRotationalMassMeasure
Rotational stiffness Derived N · m / rad ROTATIONALSTIFFNESSUNIT IfcRotationalStiffnessMeasure
Sectional area integral Derived m5 SECTIONALAREAINTEGRALUNIT IfcSectionalAreaIntegralMeasure
Section modulus Derived m3 SECTIONMODULUSUNIT IfcSectionModulusMeasure
Shear modulus Derived N / m2 SHEARMODULUSUNIT IfcShearModulusMeasure
Solid angle SI / Derived steradin sr m2 / m2 = 1 STERADIAN SOLIDANGLEUNIT IfcSolidAngleMeasure
Sound power watt W W SOUNDPOWERUNIT IfcSoundPowerMeasure
Sound power level decibel db W / W SOUNDPOWERLEVELUNIT IfcSoundPowerLevelMeasure
Sound pressure pascal Pa Pa SOUNDPRESSUREUNIT IfcSoundPressureMeasure
Sound pressure level decibel db Pa / Pa SOUNDPRESSURELEVELUNIT IfcSoundPressureLevelMeasure
Specific heat capacity Derived J / kg· K SPECIFICHEATCAPACITYUNIT IfcSpecificHeatCapacityMeasure
Temperature gradient K / m TEMPERATUREGRADIENTUNIT IfcTemperatureGradientMeasure
Temperature change K / s TEMPERATURERATEOFCHANGEUNIT IfcTemperatureRateOfChangeMeasure
- IfcText
Thermal admittance Derived W / m2 · K THERMALADMITTANCEUNIT IfcThermalAdmittanceMeasure
Thermal conductivity Derived W / m · K THERMALCONDUCTIVITYUNIT IfcThermalConductivityMeasure
Thermal expansion coefficient 1 / K THERMALEXPANSIONCOEFFICIENTUNIT IfcThermalExpansionCoefficientMeasure
Thermal resistance Derived m2 · K / W THERMALRESISTANCEUNIT IfcThermalResistanceMeasure
Thermal transmittance Derived W / m2 · K THERMALTRANSMITTANCEUNIT IfcThermalTransmittanceMeasure
Thermodynamic temperature SI / Basic kelvin K KELVIN THERMODYNAMICTEMPERATUREUNIT IfcThermodynamicTemperatureMeasure
- IfcTime (lexical representation according to ISO 8601)
Time SI / Basic second s SECOND TIMEUNIT IfcTimeMeasure
- IfcTimeStamp
Torque Derived N· m TORQUEUNIT IfcTorqueMeasure
Vapor permeability Derived kg / s · m · Pa VAPORPERMEABILITYUNIT IfcVaporPermeabilityMeasure
Volume SI / Derived cubic metre m3 m3 CUBIC_METRE VOLUMEUNIT IfcVolumeMeasure
Volumetric flow rate Derived m3 / s VOLUMETRICFLOWRATEUNIT IfcVolumetricFlowRateMeasure
Warping constant m6 WARPINGCONSTANTUNIT IfcWarpingConstantMeasure
Warping moment Derived N · m2 WARPINGMOMENTUNIT IfcWarpingMomentMeasure
Table 8.11.A — Measures and units

8.11.2 Types

  1. IfcAbsorbedDoseMeasure
  2. IfcAccelerationMeasure
  3. IfcAmountOfSubstanceMeasure
  4. IfcAngularVelocityMeasure
  5. IfcAreaDensityMeasure
  6. IfcAreaMeasure
  7. IfcBinary
  8. IfcBoolean
  9. IfcComplexNumber
  10. IfcCompoundPlaneAngleMeasure
  11. IfcContextDependentMeasure
  12. IfcCountMeasure
  13. IfcCurvatureMeasure
  14. IfcDerivedMeasureValue
  15. IfcDerivedUnitEnum
  16. IfcDescriptiveMeasure
  17. IfcDoseEquivalentMeasure
  18. IfcDynamicViscosityMeasure
  19. IfcElectricCapacitanceMeasure
  20. IfcElectricChargeMeasure
  21. IfcElectricConductanceMeasure
  22. IfcElectricCurrentMeasure
  23. IfcElectricResistanceMeasure
  24. IfcElectricVoltageMeasure
  25. IfcEnergyMeasure
  26. IfcForceMeasure
  27. IfcFrequencyMeasure
  28. IfcHeatFluxDensityMeasure
  29. IfcHeatingValueMeasure
  30. IfcIdentifier
  31. IfcIlluminanceMeasure
  32. IfcInductanceMeasure
  33. IfcInteger
  34. IfcIntegerCountRateMeasure
  35. IfcIonConcentrationMeasure
  36. IfcIsothermalMoistureCapacityMeasure
  37. IfcKinematicViscosityMeasure
  38. IfcLabel
  39. IfcLengthMeasure
  40. IfcLinearForceMeasure
  41. IfcLinearMomentMeasure
  42. IfcLinearStiffnessMeasure
  43. IfcLinearVelocityMeasure
  44. IfcLogical
  45. IfcLuminousFluxMeasure
  46. IfcLuminousIntensityDistributionMeasure
  47. IfcLuminousIntensityMeasure
  48. IfcMagneticFluxDensityMeasure
  49. IfcMagneticFluxMeasure
  50. IfcMassDensityMeasure
  51. IfcMassFlowRateMeasure
  52. IfcMassMeasure
  53. IfcMassPerLengthMeasure
  54. IfcMeasureValue
  55. IfcModulusOfElasticityMeasure
  56. IfcModulusOfLinearSubgradeReactionMeasure
  57. IfcModulusOfRotationalSubgradeReactionMeasure
  58. IfcModulusOfSubgradeReactionMeasure
  59. IfcMoistureDiffusivityMeasure
  60. IfcMolecularWeightMeasure
  61. IfcMomentOfInertiaMeasure
  62. IfcMonetaryMeasure
  63. IfcNonNegativeLengthMeasure
  64. IfcNormalisedRatioMeasure
  65. IfcNumericMeasure
  66. IfcPHMeasure
  67. IfcParameterValue
  68. IfcPlanarForceMeasure
  69. IfcPlaneAngleMeasure
  70. IfcPositiveInteger
  71. IfcPositiveLengthMeasure
  72. IfcPositivePlaneAngleMeasure
  73. IfcPositiveRatioMeasure
  74. IfcPowerMeasure
  75. IfcPressureMeasure
  76. IfcRadioActivityMeasure
  77. IfcRatioMeasure
  78. IfcReal
  79. IfcRotationalFrequencyMeasure
  80. IfcRotationalMassMeasure
  81. IfcRotationalStiffnessMeasure
  82. IfcSIPrefix
  83. IfcSIUnitName
  84. IfcSectionModulusMeasure
  85. IfcSectionalAreaIntegralMeasure
  86. IfcShearModulusMeasure
  87. IfcSimpleValue
  88. IfcSolidAngleMeasure
  89. IfcSoundPowerLevelMeasure
  90. IfcSoundPowerMeasure
  91. IfcSoundPressureLevelMeasure
  92. IfcSoundPressureMeasure
  93. IfcSpecificHeatCapacityMeasure
  94. IfcTemperatureGradientMeasure
  95. IfcTemperatureRateOfChangeMeasure
  96. IfcText
  97. IfcThermalAdmittanceMeasure
  98. IfcThermalConductivityMeasure
  99. IfcThermalExpansionCoefficientMeasure
  100. IfcThermalResistanceMeasure
  101. IfcThermalTransmittanceMeasure
  102. IfcThermodynamicTemperatureMeasure
  103. IfcTimeMeasure
  104. IfcTorqueMeasure
  105. IfcURIReference
  106. IfcUnit
  107. IfcUnitEnum
  108. IfcValue
  109. IfcVaporPermeabilityMeasure
  110. IfcVolumeMeasure
  111. IfcVolumetricFlowRateMeasure
  112. IfcWarpingConstantMeasure
  113. IfcWarpingMomentMeasure

8.11.3 Entities

  1. IfcContextDependentUnit
  2. IfcConversionBasedUnit
  3. IfcConversionBasedUnitWithOffset
  4. IfcDerivedUnit
  5. IfcDerivedUnitElement
  6. IfcDimensionalExponents
  7. IfcMeasureWithUnit
  8. IfcMonetaryUnit
  9. IfcNamedUnit
  10. IfcSIUnit
  11. IfcUnitAssignment

8.11.4 Property Sets

No resources are available in this category.

8.11.5 Quantity Sets

No resources are available in this category.

8.11.6 Functions

  1. IfcCorrectDimensions
  2. IfcCorrectUnitAssignment
  3. IfcDeriveDimensionalExponents
  4. IfcDimensionsForSIUnit

8.11.7 Rules

No resources are available in this category.

8.11.8 PropertyEnumerations

No resources are available in this category.

Edit on Github

Is this page difficult to understand? Let us know!