IfcQuantityArea

IfcQuantityArea是一个物理量，它定义了一个派生的面积度量来提供元素的物理属性。它通常由测量方法给出的特定测量规则下元素的物理性质导出。

例如，一个洞口可能有一个用于从墙面面积中扣除的洞口面积。面积的实际大小取决于所用的测量方法。

IFC2x中增加的新实体。它替换了以前IFC版本中使用的calcXxx属性。

Formal Propositions

Rule	Description
WR21	If a unit is given, the unit type shall be area unit.
WR22	A valid area quantity shall be greater than or equal to zero.

 

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
IfcPhysicalQuantity
1	Name	IfcLabel	[1:1]	Name of the element quantity or measure. The name attribute has to be made recognizable by further agreements.	X
2	Description	IfcText	[0:1]	Further explanation that might be given to the quantity.	X
	HasExternalReferences	IfcExternalReferenceRelationship @RelatedResourceObjects	S[0:?]	Reference to an external reference, e.g. library, classification, or document information, that is associated to the quantity.	X
	PartOfComplex	IfcPhysicalComplexQuantity @HasQuantities	S[0:1]	Reference to a physical complex quantity in which the physical quantity may be contained.	X
IfcPhysicalSimpleQuantity
3	Unit	IfcNamedUnit	[0:1]	Optional assignment of a unit. If no unit is given, then the global unit assignment, as established at the IfcProject, applies to the quantity measures.	X
IfcQuantityArea
4	AreaValue	IfcAreaMeasure	[1:1]	Area measure value of this quantity.	X
5	Formula	IfcLabel	[0:1]	A formula by which the quantity has been calculated. It can be assigned in addition to the actual value of the quantity. Formulas could be mathematic calculations (like width x height), database links, or a combination. The formula is for informational purposes only.	X

 

EXPRESS Specification

ENTITY IfcQuantityArea
 SUBTYPE OF (IfcPhysicalSimpleQuantity);
  AreaValue : IfcAreaMeasure;
  Formula : OPTIONAL IfcLabel;
 WHERE
  WR21 : NOT(EXISTS(SELFIfcPhysicalSimpleQuantity.Unit)) OR (SELFIfcPhysicalSimpleQuantity.Unit.UnitType = IfcUnitEnum.AREAUNIT);
  WR22 : AreaValue >= 0.;
END_ENTITY;