Extracting quantities of elements with IfcOpenShell in python

Question

I am trying to read the deepest level of quantities for objects in an ifc file, using IfcOpenShell in Python. So far I have:

import ifcopenshell

path = r'D:\ifcos_1\slab.ifc'
ifc_file = ifcopenshell.open(path)

geometries = ifc_file.by_type("IfcProduct")

for geometry in geometries:
    if geometry.is_a("IfcSlab"):
        print geometry
        test = geometry.IfcPhysicalQuantity()
        print test

I've studied the definitions

No matter which type of function I try to place for the test = geometry.X(), I get an error:

File "C:\Python27\lib\site-packages\ifcopenshell\entity_instance.py", line 48, in __getattr__
   "entity instance of type '%s' has no attribute '%s'" % (self.wrapped_data.is_a(), name))
AttributeError: entity instance of type 'IfcSlab' has no attribute 'IfcPhysicalQuantity'

Not sure how to solve this and would appreciate help.

EDIT:

Further work which gets the slab and further references:

for geometry in geometries:
    if geometry.is_a("IfcSlab"):
        print geometry
        definedBy = geometry.IsDefinedBy

        print definedBy[0]

        for each in definedBy:
            test = each.is_a()
            print test

As of this moment the obstacle is the compatibility with IFC4, which I will try to recompile with instructions from this forum post.

EDIT 2:

Further work using for now the IFC 2x3 standard, with a file that has quantity information (verified via the raw data). The following is the relevant code:

for geometry in geometries:
    if geometry.is_a("IfcSlab"):
        definedBy = geometry.IsDefinedBy

        for line in definedBy:
        test = line.is_a()
        # print test
        if line.is_a() == 'IfcRelDefinesByProperties' or line.is_a() == 'IfcRelDefinesByType':
            step1 = line.RelatingPropertyDefinition
            step2 = step1.is_a()
            print step2

There is an error no matter what I place after step1 = line., none of the following give a result:

line.IfcPropertySet
line.IfcElementQuantity
line.RelatingPropertyDefiniton

The output from this code is nevertheless:

IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcPropertySet
IfcElementQuantity
IfcElementQuantity

Which means that I can access IfcElementQuantity but none of the Attributes work. I've looked at schema reference but can't find the correct one.

Answer 1

Quantities in IFC are stored in quantity sets, which are very similar in structure to property sets. IfcOpenShell offers utility functions to extract this data in a schema-agnostic manner:

for slab in ifc_file.by_type("IfcSlab"):
    quantities = ifcopenshell.util.element.get_psets(slab, qtos_only=True)
    print(quantities) # A dictionary of qtos and quantities
    # For example print(quantities["Qto_SlabBaseQuantities"]["GrossVolume"])

Answer 2

I wrote a few functions once, to extract all properties.

https://github.com/johannesmichael/ifc-python/blob/master/modules/ifc_pset_utils.py

Might not be complete, but can give you an idea. I extract all to excel for further analyzis.

BaseQuantities:

def get_related_quantities(ifc_instance):
"""
Returns a list of IfcElementQuantity for given IFC ID
argument: ifc_instance
return: list of property sets
"""
quantities_list =[]
for x in ifc_instance.IsDefinedBy:
    if x.is_a("IfcRelDefinesByProperties"):
        if x.RelatingPropertyDefinition.is_a("IfcElementQuantity"):
            quantities_list.append(x.RelatingPropertyDefinition)
return quantities_list  

def get_quantity_single_value(x):
"""
Returns a dict of dicts of IfcElementQuantity single values.
Returning a dictionary of dictionaries
is used, because it is easy to transform to pandas.DataFrame 
argument: IFC Element as contained in list from get_related_property_sets()
return: dict of property single values like {"IfcName":"xx", "IfcGlobalId": "klkhlkh", ......}
"""
quantities_dicts = {}
for y in x.Quantities:
    if y.is_a('IfcQuantityArea'):
        quantities_dicts.update({y.Name:y.AreaValue})
    if y.is_a('IfcQuantityLength'):
        quantities_dicts.update({y.Name:y.LengthValue})
    if y.is_a('IfcQuantityVolume'):
        quantities_dicts.update({y.Name:y.VolumeValue})
    if y.is_a('IfcQuantityCount'):
        quantities_dicts.update({y.Name:y.CountValue})
    if y.is_a('IfcQuantityWeight'):
        quantities_dicts.update({y.Name:y.WeightValue})

return quantities_dicts 

This was done for IFC 2x3 TC1 Hope that helps

Answer 3

When implementing this you should take care which version of IFC your import library works on - the version distributed by the IfcOpenShell-Website works with IFC2X3. For IFC4 you will probably need to compile a version yourself. (you can check your IFC version with ifcopenshell.schema_identifier)

I am putting links up to the buildingSMART IFC 4 definition even if I am talking about IFC2X3. Differences to IFC2X3 are marked in red on the buildingSMART web page. And the IFC4 definition is nicer to read (IMO).

Quantities aren't directly attached like an attribute. They are written as property sets and then related to the element or element type. So first you should ensure your IFC file contains quantities - otherwise you will not find any. Usually you start with a specific product - ifc_file.by_type('IfcSlab'). You can reach the property sets via inverse attributes - those are usually set up by the IFC library, they don't appear directly as attribute in the file.

I took you example file and shortened it to about a third (so it's still a valid IFC2X3 file):

ISO-10303-21;
HEADER;FILE_DESCRIPTION(('ViewDefinition [Custom, QuantityTakeOffAddOnView, SpaceBoundary2ndLevelAddOnView]','Option [Drawing Scale: 100.000000]','Option [Global Unique Identifiers (GUID): Keep existing]','Option [Elements to export: Visible elements (on all stories)]','Option [Partial Structure Display: Entire Model]','Option [IFC Domain: All]','Option [Structural Function: All Elements]','Option [Convert Grid elements: On]','Option [Convert IFC Annotations and ARCHICAD 2D elements: Off]','Option [Convert 2D symbols of Doors and Windows: Off]','Option [Explode Composite and Complex Profile elements into parts: On]','Option [Export geometries that Participates in Collision Detection only: Off]','Option [Elements in Solid Element Operations: Extruded/revolved]','Option [Elements with junctions: Extruded/revolved without junctions]','Option [Slabs with slanted edge(s): Extruded]','Option [Use legacy geometric methods as in Coordination View 1.0: Off]','Option [IFC Site Geometry: As boundary representation (BRep)]','Option [IFC Site Location: At Project Origin]','Option [Curtain Wall export mode: Container Element]','Option [Railing export mode: Single Element]','Option [Stair export mode: Container Element]','Option [Properties To Export: All properties]','Option [Space containment: On]','Option [IFC Domain For Space Containment: All]','Option [Bounding Box: Off]','Option [Geometry to type objects: Off]','Option [Element Properties: All]','Option [Property Type Element Parameter: On]','Option [Quantity Type Element Parameter: On]','Option [IFC Base Quantities: On]','Option [Window Door Lining and Panel Parameters: On]','Option [IFC Space boundaries: On]','Option [ARCHICAD Zone Categories as IFC Space classification data: On]','Option [Element Classifications: On]'),'2;1');
FILE_NAME('D:\\Side Projects\\Paragraph3\\The database\\IFC Files\\Local tests\\ifcos_1\\slab.ifc','2018-06-13T18:28:40',('Architect'),('Building Designer Office'),'The EXPRESS Data Manager Version 5.02.0100.09 : 26 Sep 2013','IFC file generated by GRAPHISOFT ARCHICAD-64 21.0.0 INT FULL Windows version (IFC2x3 add-on version: 3005 INT FULL).','The authorising person');
FILE_SCHEMA(('IFC2X3'));
ENDSEC;
DATA;
#1= IFCPERSON($,'Undefined',$,$,$,$,$,$);
#7= IFCPERSONANDORGANIZATION(#1,#10,$);
#10= IFCORGANIZATION('GS','GRAPHISOFT','GRAPHISOFT',$,$);
#11= IFCAPPLICATION(#10,'21.0.0','ARCHICAD-64','IFC2x3 add-on version: 3005 INT FULL');
#12= IFCOWNERHISTORY(#7,#11,$,.ADDED.,$,$,$,1528907320);
#13= IFCSIUNIT(*,.LENGTHUNIT.,.MILLI.,.METRE.);
#14= IFCSIUNIT(*,.AREAUNIT.,$,.SQUARE_METRE.);
#16= IFCSIUNIT(*,.PLANEANGLEUNIT.,$,.RADIAN.);
#17= IFCMEASUREWITHUNIT(IFCPLANEANGLEMEASURE(0.0174532925199),#16);
#18= IFCDIMENSIONALEXPONENTS(0,0,0,0,0,0,0);
#19= IFCCONVERSIONBASEDUNIT(#18,.PLANEANGLEUNIT.,'DEGREE',#17);
#29= IFCUNITASSIGNMENT((#13,#14,#19));
#31= IFCDIRECTION((1.,0.,0.));
#35= IFCDIRECTION((0.,0.,1.));
#37= IFCCARTESIANPOINT((0.,0.,0.));
#39= IFCAXIS2PLACEMENT3D(#37,#35,#31);
#40= IFCDIRECTION((0.,1.));
#42= IFCGEOMETRICREPRESENTATIONCONTEXT($,'Model',3,1.00000000000E-5,#39,#40);
#45= IFCPROJECT('344O7vICcwH8qAEnwJDjSU',#12,'Project',$,$,$,$,(#42),#29);
#59= IFCLOCALPLACEMENT($,#39);
#62= IFCSITE('20FpTZCqJy2vhVJYtjuIce',#12,'Site',$,$,#59,$,$,.ELEMENT.,(47,33,34,948800),(19,3,17,204400),0.,$,$);
#68= IFCRELAGGREGATES('0Du7$nzQXCktKlPUTLFSAT',#12,$,$,#45,(#62));
#74= IFCQUANTITYLENGTH('GrossPerimeter',$,$,0.);
#76= IFCQUANTITYAREA('GrossArea',$,$,0.);
#77= IFCELEMENTQUANTITY('2GNZepdf73fvGc$0W6rozj',#12,'BaseQuantities',$,'ARCHICAD BIM Base Quantities',(#74,#76));
#82= IFCRELDEFINESBYPROPERTIES('2Hm9JvZjohDNSD2kdxZI3b',#12,$,$,(#62),#77);
#93= IFCLOCALPLACEMENT(#59,#39);
#95= IFCBUILDING('00tMo7QcxqWdIGvc4sMN2A',#12,'Building',$,$,#93,$,$,.ELEMENT.,$,$,$);
#97= IFCRELAGGREGATES('2b_h_mYcGArd6glJG2Fmbt',#12,$,$,#62,(#95));
#101= IFCQUANTITYAREA('GrossFloorArea',$,$,0.);
#102= IFCELEMENTQUANTITY('1kQMlmT0rD35a9E43iKTas',#12,'BaseQuantities',$,'ARCHICAD BIM Base Quantities',(#101));
#104= IFCRELDEFINESBYPROPERTIES('0L87OdSD3DqSTjSRlAciZL',#12,$,$,(#95),#102);
#115= IFCLOCALPLACEMENT(#93,#39);
#117= IFCBUILDINGSTOREY('1oZ0wPs_PE8ANCPg3bIs4j',#12,'Ground Floor',$,$,#115,$,$,.ELEMENT.,0.);
#119= IFCRELAGGREGATES('118jwqMnuwK1xuf97w7fU5',#12,$,$,#95,(#117));
#180= IFCSLAB('3W29Drc$H6CxK3FGIxjJNl',#12,'SLA - 001',$,$,$,$,'E0089375-9BF4-4633-B503-3D04BBB535EF',.FLOOR.);
#195= IFCRELCONTAINEDINSPATIALSTRUCTURE('04ldtj6cp2dME6CiP80Bzh',#12,$,$,(#180),#117);
#326= IFCPROPERTYSINGLEVALUE('Fragility rating',$,IFCLABEL('0'),$);
#327= IFCPROPERTYSINGLEVALUE('Tile dimensions',$,IFCLABEL('Undefined'),$);
#328= IFCPROPERTYSINGLEVALUE('Anti-static Surface',$,IFCBOOLEAN(.F.),$);
#329= IFCPROPERTYSINGLEVALUE('Non-skid Surface',$,IFCBOOLEAN(.F.),$);
#330= IFCPROPERTYSET('0LYX8AqOOS9ft8M4aJYEYa',#12,'FLOORINGS',$,(#326,#327,#328,#329));
#332= IFCRELDEFINESBYPROPERTIES('1G6WWCSQGg0PdTnW7hwMrM',#12,$,$,(#180),#330);
#335= IFCPROPERTYSINGLEVALUE('Renovation Status',$,IFCLABEL('Existing'),$);
#336= IFCPROPERTYSET('0cR6wsk2QWcLKPchA8mF3u',#12,'AC_Pset_RenovationAndPhasing',$,(#335));
#338= IFCRELDEFINESBYPROPERTIES('3nYD8KGPhoBw5okmj1JjsA',#12,$,$,(#180),#336);
#341= IFCQUANTITYLENGTH('Width',$,$,300.);
#342= IFCQUANTITYLENGTH('Perimeter',$,$,22000.);
#343= IFCQUANTITYAREA('GrossArea',$,$,28.);
#344= IFCQUANTITYAREA('NetArea',$,$,28.);
#345= IFCQUANTITYVOLUME('GrossVolume',$,$,8.4);
#346= IFCQUANTITYVOLUME('NetVolume',$,$,8.4);
#347= IFCELEMENTQUANTITY('1RfXJewSc7OCIaD$L2ZoXT',#12,'BaseQuantities',$,'ARCHICAD BIM Base Quantities',(#341,#342,#343,#344,#345,#346));
#349= IFCRELDEFINESBYPROPERTIES('085uLttAQRllG3nL_YikZ8',#12,$,$,(#180),#347);
#375= IFCQUANTITYVOLUME('Gross Volume of the Slab',$,$,8.4);
#376= IFCQUANTITYVOLUME('Gross Volume of the Slab with Holes',$,$,8.4);
#377= IFCQUANTITYLENGTH('Holes Perimeter',$,$,0.);
#378= IFCQUANTITYAREA('Holes Surface Area',$,$,0.);
#379= IFCQUANTITYLENGTH('Perimeter',$,$,22000.);
#381= IFCQUANTITYAREA('Top Surface Area',$,$,28.);
#382= IFCELEMENTQUANTITY('0DuZ12CVtssgcIQPaQ$1sp',#12,'ArchiCADQuantities',$,'ARCHICAD BIM Quantities',(#375,#376,#377,#378,#379,#381));
#384= IFCRELDEFINESBYPROPERTIES('0KgGv0Y8Fc2jg8BCPhxnM5',#12,$,$,(#180),#382);
#393= IFCSLABTYPE('0K1otpnkQcEpOBXPxnZ3dB',#12,'Timber - Floor 300',$,$,(#396),$,'14072DF3-C6E6-A63B-360B-859EF18C39CB',$,.FLOOR.);
#395= IFCRELDEFINESBYTYPE('353egCMRpZtJd$CDCoSsCb',#12,$,$,(#180),#393);
#352= IFCQUANTITYAREA('Area',$,$,28.);
#353= IFCQUANTITYLENGTH('Height',$,$,300.);
#354= IFCQUANTITYVOLUME('Net Volume',$,$,8.4);
#396= IFCELEMENTQUANTITY('1Zyxf4r7NogSp4V7ORMpET',#12,'ArchiCADQuantities',$,'ARCHICAD BIM Quantities',(#352,#353,#354));
ENDSEC;
END-ISO-10303-21;

This is a slab with an area measurement attached. It should have an inverse attribute IsDefinedBy. In IFC2X3 this points to a list of entities IfcRelDefinesByProperties and IfcRelDefinesByType. With IFC4 IfcRelDefinesByType will be put in the inverse attribute IsTypedBy.

Each IfcRelDefinesByProperties point to a property set in their attribute RelatingPropertyDefinition. There are various property set types, you want it to be of type IfcElementQuantity when searching for physical quantities. You will have to check at run time which type you currently hold while iterating the list of property relations.

The quantity set has a list of IfcPhysicalQuantities attached in the attribute Quantities. These can be simple quantities or complex quantities, which are composed of multiple simple quantities. For simple quantities there are specific subtypes for area, count or weight. Again you will have to check at runtime for the concrete type.

The area quantity itself has a name and description to give further context (not ours, but possibly in the real world). The value attribute is named after the quantity type, so IfcQuantityArea has an attribute AreaValue. Also of interest is attribute Unit which is a reference to the unit of the value. If it is not set (as in our example) you will need to look for assigned units at the IfcProject entity.

Unfortunately this might not be all. If the object (here our IfcSlab) has an assigned object type, that type can also have property sets attached (I modified the example file to be this case). Thy type entity does not have an inverse attribute, but a direct one, HasProperties. If it is set, you can discover attached properties through it.

To summarise, you will probably need multiple loops:

1. For each object, get property sets
2. For each property set, test if it is quantity set
3. For each quantity set, go through quantities

And potentially repeat this search if the object has a user defined type.

The following code should do exactly this (written on my machine with python 3.5.4 and ifcopenshell with IFC2X3 schema)):

1. Get all slabs from the file (there is only one)
2. Go through all entities in the inverse attribute IsDefinedBy - these can be IfcRelDefinesByProperties or IFcRelDefinesByType.
3. Get property sets from the entity
4. Check if the given property set is IfcElementQuantity and proceed to print quantitites if it is.

import ifcopenshell
def print_quantities(property_definition):
  if 'IfcElementQuantity' == property_definition.is_a():
    for quantity in property_definition.Quantities:
      if 'IfcQuantityArea' == quantity.is_a():
        print('Area value: ' + str(quantity.AreaValue))
      if 'IfcQuantityVolume' == quantity.is_a():
        print('Volume value: ' + str(quantity.VolumeValue))
      if 'IfcQuantityLength' == quantity.is_a():
        print('Length value: ' + str(quantity.LengthValue))

ifc_file = ifcopenshell.open('slab.ifc')
products = ifc_file.by_type('IfcSlab')
for product in products:
  if product.IsDefinedBy:
    definitions = product.IsDefinedBy
    for definition in definitions:
      #In IFC2X3 this could be property or type
      #in IFC4 type is in inverse attribute IsTypedBy
      if 'IfcRelDefinesByProperties' == definition.is_a():
        property_definition = definition.RelatingPropertyDefinition
        print_quantities(property_definition)
      if 'IfcRelDefinesByType' == definition.is_a():
        type = definition.RelatingType
        if type.HasPropertySets:
          for property_definition in type.HasPropertySets:
            print_quantities(property_definition)

For the example this results in:

Length value: 300.0
Length value: 22000.0
Area value: 28.0
Area value: 28.0
Volume value: 8.4
Volume value: 8.4
Volume value: 8.4
Volume value: 8.4
Length value: 0.0
Area value: 0.0
Length value: 22000.0
Area value: 28.0
Area value: 28.0
Length value: 300.0
Volume value: 8.4