IfcAlignment

Item	SPF	XML	Change	Description
IFC4x1 Release Candidate 1
IfcAlignment			ADDED
IFC4x1 Release Candidate 2
IfcAlignment
Axis	X	X	MODIFIED	Name changed from PredefinedType to Axis. Type changed from IfcAlignmentTypeEnum to IfcBoundedCurve. Instantiation changed from OPTIONAL.
PredefinedType	X	X	MODIFIED	Name changed from Horizontal to PredefinedType. Type changed from IfcAlignment2DHorizontal to IfcAlignmentTypeEnum.
Vertical	X		DELETED
LinearRefMethod	X		DELETED

Semantic definitions at the entity

Entity definition

An alignment is used to define a reference system to position elements mainly for linear construction works, such as roads, rails, bridges, and others. The relative positioning along the alignment is defined by the linear referencing methodology.

NOTE See ISO 19148 Geographic information – Linear referencing for general definitions about linear referencing.

A single alignment may have:

a horizontal alignment defined in the x/y plane of the engineering coordinate system
an accompanying vertical alignment, defined along the horizontal alignment in the distance along / z coordinate space
a relative alignment, defined as a span within another alignment and/or at constant or variable offsets
a 3D alignment, either computed from the horizontal and vertical alignment, or extracted from geospatial data.

Alignments may be aggregated into referents (IfcReferent) or derivative alignments. Derivative alignments may be used to indicate dependent alignments, such as an alignment for a bridge that is relative to a parent alignment for a road, where the child IfcAlignment may have Axis set to IfcOffsetCurveByDistances that starts and ends at a span within the extent of the IfcAlignmentCurve defined at the Axis of the parent IfcAlignment.

Alignments may be assigned to groups using IfcRelAssignsToGroup, where IfcGroup or subtypes may capture information common to multiple alignments.

Supported representations of IfcAlignment.Axis are:

IfcAlignmentCurve as a 3D horizontal and vertical alignment (represented by their alignment segments)
IfcAlignmentCurve as a 2D horizontal alignment (represented by its horizontal alignment segments) without a vertical alignment
IfcOffsetCurveByDistances as a 2D or 3D curve defined relative to an IfcAlignmentCurve or another IfcOffsetCurveByDistances
IfcPolyline as a 3D alignment by a 3D polyline representation (such as coming from a survey)
IfcPolyline as a 2D horizontal alignment by a 2D polyline representation (such as in very early planning phases or as a map representation)

NOTE Although Axis is an IfcCurve base type, only derived types IfcAlignmentCurve, IfcOffsetCurveByDistances, and IfcPolyline are meant to be supported types. Derivative specifications (Model View Definitions) may expand this set to include additional curve types.

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
9	PredefinedType	IfcAlignmentTypeEnum	?	Predefined generic types for an alignment that are specified in an enumeration. NOTE This attribute is reserved for future use.	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
IfcRoot
1	GlobalId	IfcGloballyUniqueId		Assignment of a globally unique identifier within the entire software world.	X
2	OwnerHistory	IfcOwnerHistory	?	Assignment of the information about the current ownership of that object, including owning actor, application, local identification and information captured about the recent changes of the object, NOTE only the last modification in stored - either as addition, deletion or modification. IFC4 CHANGE The attribute has been changed to be OPTIONAL.	X
3	Name	IfcLabel	?	Optional name for use by the participating software systems or users. For some subtypes of IfcRoot the insertion of the Name attribute may be required. This would be enforced by a where rule.	X
4	Description	IfcText	?	Optional description, provided for exchanging informative comments.	X
IfcObjectDefinition
	HasAssignments	IfcRelAssigns @RelatedObjects	S[0:?]	Reference to the relationship objects, that assign (by an association relationship) other subtypes of IfcObject to this object instance. Examples are the association to products, processes, controls, resources or groups.	X
	Nests	IfcRelNests @RelatedObjects	S[0:1]	References to the decomposition relationship being a nesting. It determines that this object definition is a part within an ordered whole/part decomposition relationship. An object occurrence or type can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been added and separated from Decomposes defined at IfcObjectDefinition.	X
	IsNestedBy	IfcRelNests @RelatingObject	S[0:?]	References to the decomposition relationship being a nesting. It determines that this object definition is the whole within an ordered whole/part decomposition relationship. An object or object type can be nested by several other objects (occurrences or types). IFC4 CHANGE The inverse attribute datatype has been added and separated from IsDecomposedBy defined at IfcObjectDefinition.	X
	HasContext	IfcRelDeclares @RelatedDefinitions	S[0:1]	References to the context providing context information such as project unit or representation context. It should only be asserted for the uppermost non-spatial object. IFC4 CHANGE The inverse attribute datatype has been added.	X
	IsDecomposedBy	IfcRelAggregates @RelatingObject	S[0:?]	References to the decomposition relationship being an aggregation. It determines that this object definition is whole within an unordered whole/part decomposition relationship. An object definitions can be aggregated by several other objects (occurrences or parts). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	X
	Decomposes	IfcRelAggregates @RelatedObjects	S[0:1]	References to the decomposition relationship being an aggregation. It determines that this object definition is a part within an unordered whole/part decomposition relationship. An object definitions can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	X
	HasAssociations	IfcRelAssociates @RelatedObjects	S[0:?]	Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification.	X
IfcObject
5	ObjectType	IfcLabel	?	The type denotes a particular type that indicates the object further. The use has to be established at the level of instantiable subtypes. In particular it holds the user defined type, if the enumeration of the attribute PredefinedType is set to USERDEFINED.	X
	IsDeclaredBy	IfcRelDefinesByObject @RelatedObjects	S[0:1]	Link to the relationship object pointing to the declaring object that provides the object definitions for this object occurrence. The declaring object has to be part of an object type decomposition. The associated IfcObject, or its subtypes, contains the specific information (as part of a type, or style, definition), that is common to all reflected instances of the declaring IfcObject, or its subtypes. IFC4 CHANGE New inverse relationship, change made with upward compatibility for file based exchange.	X
	Declares	IfcRelDefinesByObject @RelatingObject	S[0:?]	Link to the relationship object pointing to the reflected object(s) that receives the object definitions. The reflected object has to be part of an object occurrence decomposition. The associated IfcObject, or its subtypes, provides the specific information (as part of a type, or style, definition), that is common to all reflected instances of the declaring IfcObject, or its subtypes. IFC4 CHANGE New inverse relationship, change made with upward compatibility for file based exchange.	X
	IsTypedBy	IfcRelDefinesByType @RelatedObjects	S[0:1]	Set of relationships to the object type that provides the type definitions for this object occurrence. The then associated IfcTypeObject, or its subtypes, contains the specific information (or type, or style), that is common to all instances of IfcObject, or its subtypes, referring to the same type. IFC4 CHANGE New inverse relationship, the link to IfcRelDefinesByType had previously be included in the inverse relationship IfcRelDefines. Change made with upward compatibility for file based exchange.	X
	IsDefinedBy	IfcRelDefinesByProperties @RelatedObjects	S[0:?]	Set of relationships to property set definitions attached to this object. Those statically or dynamically defined properties contain alphanumeric information content that further defines the object. IFC4 CHANGE The data type has been changed from IfcRelDefines to IfcRelDefinesByProperties with upward compatibility for file based exchange.	X
IfcProduct
6	ObjectPlacement	IfcObjectPlacement	?	Placement of the product in space, the placement can either be absolute (relative to the world coordinate system), relative (relative to the object placement of another product), or constraint (e.g. relative to grid axes). It is determined by the various subtypes of IfcObjectPlacement, which includes the axis placement information to determine the transformation for the object coordinate system.	X
7	Representation	IfcProductRepresentation	?	Reference to the representations of the product, being either a representation (IfcProductRepresentation) or as a special case a shape representations (IfcProductDefinitionShape). The product definition shape provides for multiple geometric representations of the shape property of the object within the same object coordinate system, defined by the object placement.	X
	ReferencedBy	IfcRelAssignsToProduct @RelatingProduct	S[0:?]	Reference to the IfcRelAssignsToProduct relationship, by which other products, processes, controls, resources or actors (as subtypes of IfcObjectDefinition) can be related to this product.	X
IfcPositioningElement
	ContainedInStructure	IfcRelContainedInSpatialStructure @RelatedElements	S[0:1]	Relationship to a spatial structure element, to which the positioning element is primarily associated. IFC2x CHANGE The inverse relationship has been added to IfcGrid with upward compatibility IFC4 CHANGE The inverse relationship has been promoted from IfcGrid to this new supertype with upward compatibility	X
IfcLinearPositioningElement
8	Axis	IfcCurve		The curve to be used for positioning.	X
IfcAlignment
9	PredefinedType	IfcAlignmentTypeEnum	?	Predefined generic types for an alignment that are specified in an enumeration. NOTE This attribute is reserved for future use.	X

Definitions applying to General Usage

Instance diagram

Concept usage

Alignment Attributes

The Alignment Attributes concept applies to this entity.

mvdXML Specification


<?xml version="1.0"?>

<ConceptRoot xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" uuid="733a949d-1cc8-4d40-bd6a-3836e3c195dd" name="IfcAlignment" status="sample" applicableRootEntity="IfcAlignment">

  <Applicability uuid="00000000-0000-0000-0000-000000000000" status="sample">

    <Template ref="04071b90-2b54-4545-8eba-f18c472ebcbe" />

    <TemplateRules operator="and" />

  </Applicability>

  <Concepts>

    <Concept uuid="d0249472-003e-4fc6-a663-6d8d44069c31" name="Alignment Attributes" status="sample" override="false">

      <Template ref="48afbff3-893b-4791-94dd-fface6eac658" />

    </Concept>

  </Concepts>

</ConceptRoot>

Concept inheritance

#	Concept	Template	Model View
IfcRoot
	Identity	Software Identity	General Usage
	Revision Control	Revision Control	General Usage
IfcObjectDefinition
	Classification Association	Classification Association	General Usage
IfcObject
	Object User Identity	Object User Identity	General Usage
	Object Predefined Type	Object Predefined Type	General Usage
	Object Typing	Object Typing	General Usage
	Property Sets for Objects	Property Sets for Objects	General Usage
	Property Sets with Override	Property Sets with Override	General Usage
IfcProduct
	Product Placement	Product Placement	General Usage
	Product Geometric Representation	Product Geometric Representation	General Usage
IfcPositioningElement
	Placement	Product Local Placement	General Usage
	Footprint Geometry	FootPrint Geometry	General Usage
IfcAlignment
	Alignment Attributes	Alignment Attributes	General Usage

IfcAlignment

Semantic definitions at the entity

Inherited definitions from supertypes

Definitions applying to General Usage

Examples

Formal representations