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Definition from IAI: An IfcElementQuantity defines a set of derived measures of an element's physical property. Elements could be spatial structure elements (like buildings, storeys, or spaces) or building elements (like walls, slabs, finishes). The IfcElementQuantity gets assigned to the element by using the IfcRelDefinesByProperties relationship.

The optional MethodOfMeasurement attribute defines the code, e.g. from a standard method of measurement, which had been used to calculate the element quantity.

NOTE The recognizable values for the name and the method of measurement attributes have to be agreed upon in further agreement documents, such as implementers agreements. Some of these agreements might be limited to a certain region, to which the method of measurement applies.

The name attribute, given at the individual Quantities provides a recognizable semantic meaning of the element quantity. Both information is needed to establish a precise meaning for the measure value. An optional description may be assigned to each of the Quantities. All quantities assigned by a single instance of IfcElementQuantity are deemed to have been generated according to the same method of measurement. However several instances of IfcElementQuantity are assignable to an element, thus allowing for an element having quantities generated according to several methods of measurement.

EXAMPLE1 To exchange the net floor area of spaces in the German region (as IfcSpace), the name might be 'HNF1' (area of main function type 1), and the method of measurement might be accordingly 'DIN277' (German industry norm no. 277)

EXAMPLE2 The same instance of IfcSpace may have a different area measure assigned in the German region according to a housing regulation, the name would be 'Wohnfläche' and the method of measurement would be '2.BV'. It would be attached to the IfcSpace by a separate IfcRelDefinesByProperties relationship.

The IfcElementQuantity can have the following subtypes of IfcPhysicalQuantity within its SET of Quantities, which count for the basis measure types used:

HISTORY New entity in IFC Release 2x. NOTE: It replaces the calcXxx attributes used in previous IFC Releases.

EXPRESS specification:

ENTITY IfcElementQuantity
SUBTYPE OF ( IfcPropertySetDefinition);
MethodOfMeasurement  :  OPTIONAL IfcLabel;
Quantities  :  SET [1:?] OF IfcPhysicalQuantity;

Attribute definitions:

MethodOfMeasurement  :  Name of the method of measurement used to calculate the element quantity. The method of measurement attribute has to be made recognizable by further agreements.
IFC2x2 Addendum 1 change: The attribute has been changed to be optional
Quantities  :  The individual quantities for the element, can be a set of length, area, volume, weight or count based quantities.

Inheritance graph

ENTITY IfcElementQuantity;
GlobalId  :  IfcGloballyUniqueId;
OwnerHistory  :  IfcOwnerHistory;
Name  :  OPTIONAL IfcLabel;
Description  :  OPTIONAL IfcText;
ENTITY IfcPropertyDefinition;
HasAssociations  :  SET OF IfcRelAssociates FOR RelatedObjects;
ENTITY IfcPropertySetDefinition;
PropertyDefinitionOf  :  SET [0:1] OF IfcRelDefinesByProperties FOR RelatingPropertyDefinition;
DefinesType  :  SET [0:1] OF IfcTypeObject FOR HasPropertySets;
ENTITY IfcElementQuantity;
MethodOfMeasurement  :  OPTIONAL IfcLabel;
Quantities  :  SET [1:?] OF IfcPhysicalQuantity;