IfcQuantityLength

IfcQuantityLength是一个物理量，它定义了一个派生的长度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。

示例：屋顶结构内的椽可根据其长度进行测量（考虑公共横截面）。长度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 a length unit.
WR22	A valid length 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
IfcQuantityLength
4	LengthValue	IfcLengthMeasure	[1:1]	Length 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 IfcQuantityLength
 SUBTYPE OF (IfcPhysicalSimpleQuantity);
  LengthValue : IfcLengthMeasure;
  Formula : OPTIONAL IfcLabel;
 WHERE
  WR21 : NOT(EXISTS(SELFIfcPhysicalSimpleQuantity.Unit)) OR (SELFIfcPhysicalSimpleQuantity.Unit.UnitType = IfcUnitEnum.LENGTHUNIT);
  WR22 : LengthValue >= 0.;
END_ENTITY;