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Extracting object properties from an IFC file with IfcOpenShell

Besides the object geometry information, IFC files may contain properties for the IFC objects. The properties can be, for example, some predefined dimension information such as an object volume or a choice of material. Some of the properties are predefined in the IFC standards, but custom ones can be added.

IFC files can be massive and resource-intensive to process, so in some cases, it helps to separate the object properties from the geometry data.

IfcOpenShell is a toolset for processing IFC files. It is written mostly in C++ but also provides a Python interface.

To read an IFC file

>>> ifc_file = ifcopenshell.open("model.ifc")

Fetch all objects of type IfcSlab

>>> slab = ifc_file.by_type("IfcSlab")[1]

Get the list of properties

>>> slab.IsDefinedBy
(#145075=IfcRelDefinesByType('2_fok0__fAcBZmMlQcYwie',#1,$,$,(#27,#59),#145074), #145140=IfcRelDefinesByProperties('3U2LyORgXC2f_hWf6I16C1',#1,$,$,(#27,#59),#145141), #145142=IfcRelDefinesByProperties('2M__N9P55FIx5SxaSe9VVF',#1,$,$,(#27,#59),#145143), #145144=IfcRelDefinesByProperties('0wZfYbFufCg9P3Ppg0Tss4',#1,$,$,(#27,#59),#145145), #145146=IfcRelDefinesByProperties('1jVU$$d$T6jB2JQ0igcqpd',#1,$,$,(#59),#145147))

Pull one property set

>>> one_property_set = slab.IsDefinedBy[1].RelatingPropertyDefinition
>>> one_property_set
#145141=IfcPropertySet('0uC5dGWlrFSx9IjsHVaS8x',#1,'A property set name',$,(#145133,#145134))

List its properties

>>> one_property_set.HasProperties
(#145133=IfcPropertySingleValue('Floor',$,IfcText('Floor 0'),$), #145134=IfcPropertySingleValue('Some custom value',$,IfcText('Value'),$))

Properties can also be numeric values with units

>>> another_property_set.HasProperties
(#145135=IfcPropertySingleValue('Thickness',$,IfcLengthMeasure(2.E-1),$), #145138=IfcPropertySingleValue('Volume',$,IfcVolumeMeasure(7.19999999999365E-2),$), #145136=IfcPropertySingleValue('Net Area',$,IfcAreaMeasure(3.60000015625E-1),$), #145137=IfcPropertySingleValue('Perimeter',$,IfcLengthMeasure(2.39999984374577),$))

The units are defined in the IFC project metadata. In this example, the length units (IfcLengthMeasure) are in meters

>>> project = ifc_file.by_type("IfcProject")[0]
>>> units = project.UnitsInContext.Units
>>> units[2]
#152046=IfcSIUnit(*,.LENGTHUNIT.,$,.METRE.)
>>> units[2].UnitType
'LENGTHUNIT'
>>> units[2].Name
'METRE'

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