IfcAlignment2DVerticalSegment

Item	SPF	XML	Change	Description
IFC4x1 Release Candidate 1
IfcAlignment2DVerticalSegment			ADDED

Semantic definitions at the entity

Entity definition

Individual segment along the IfcAlignment2DVertical, being defined in the distance-along/z coordinate space.

The vertical alignment is defined by segments that connects end-to-start. The vertical alignment curve geometry is defined in a plane with x = distance along horizontal, the y = height (or elevation). The transition at the segment connection is not enforced to be tangential, if the “tangential continuity” flag is set to false, otherwise a tangential continuity shall be preserved.

The following vertical segment types are defined:

line segment - IfcAlignment2DVerSegLine
circular arc segment - IfcAlignment2DVerSegCircularArc
parabolic arc segment - IfcAlignment2DVerSegParabolicArc which can describe symmetric and unsymmetric parabolas

For each vertical segment, the following non-redundant information is provided:

the start point (in distance along/ height coordinates)
the start gradient (as a ratio measure with horizontal being 0, uphill positive, and downhill negative) usually between 1 < n < -1 (equal to a percentage of 100% < n < -100%, or to a degree of 45° < n < -45° but higher values are possible)
the length (as horizontal length along the distance along (not the curve segment length))
the curve parameter needed for circular and parabolic arc segments

The following information can be calculated (and is therefore not exchanged explicitly to avoid redundancy and inconsistencies)

the end distance along (from the distance along and segment length)
the end height (from start distance along, gradient, length and curve parameter)
the end direction (from start direction, segment length and curve parameter)
the point of vertical intersection (from start direction and end direction)

The following checks can be done to validate the correct exchange:

continuity – does the calculated end distance along of the previous segment matches with the provided start distance along of this segment
tangential continuity – does the calculated end gradient of the previous segment matches with the provided start gradient of this segment

NOTE Specific subtypes of the IfcAlignment2DVerticalSegment add specific geometric curve parameters. Connectivity between vertical segments is not necessarily tangential, but this can be enforced as a requirement through the attribute TangentialContinuity.

Figure 314 — Alignment vertical segment

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
4	StartDistAlong	IfcLengthMeasure		Distance along the horizontal alignment, measured along the IfcAlignment2DHorizontal given in the length unit of the global IfcUnitAssignment.	X
5	HorizontalLength	IfcPositiveLengthMeasure		Length measured as distance along the horizontal alignment of the segment.	X
6	StartHeight	IfcLengthMeasure		Elevation in Z of the start point relative to the IfcAlignment coordinate system. NOTE It is strongly advised to not offset the IfcAlignment coordinate system from the project engineering coordinate system.	X
7	StartGradient	IfcRatioMeasure		Gradient of the tangent of the vertical segment at the start point. It is provided as a ratio measure. The ratio is percentage/100 (0.1 is equal to 10%). It has a theoretical range of -∞ < n < ∞ using a ratio measure. The equivalent range measured in degree is -90° < n < 90°. NOTE For practical application of start gradient, the range of the ratio measure should be within the limits of -1 ≤ n ≤ 1 (equivalent in degree -45° ≤ n ≤ 45°). However larger limits might apply for particular usages. Positive gradient means an increasing height at the start (or uphill), a negative gradient means decreasing height at the start (or downhill).	X
	ToVertical	IfcAlignment2DVertical @Segments	S[1:1]		X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
IfcRepresentationItem
	LayerAssignment	IfcPresentationLayerAssignment @AssignedItems	S[0:1]	Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items. IFC2x3 CHANGE The inverse attribute LayerAssignments has been added. IFC4 CHANGE The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed.	X
	StyledByItem	IfcStyledItem @Item	S[0:1]	Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. IFC2x3 CHANGE The inverse attribute StyledByItem has been added.	X
IfcGeometricRepresentationItem
IfcAlignment2DSegment
1	TangentialContinuity	IfcBoolean	?	Connectivity between the continuous segments is not enforced per se to be tangential. Setting "TangentialContinuity" to True means that the current segment shall continue with tangential continuity to the previous one.	X
2	StartTag	IfcLabel	?	Tag to annotate the start point of the alignment segment.	X
3	EndTag	IfcLabel	?	Tag to annotate the end point of the alignment segment.	X
IfcAlignment2DVerticalSegment
4	StartDistAlong	IfcLengthMeasure		Distance along the horizontal alignment, measured along the IfcAlignment2DHorizontal given in the length unit of the global IfcUnitAssignment.	X
5	HorizontalLength	IfcPositiveLengthMeasure		Length measured as distance along the horizontal alignment of the segment.	X
6	StartHeight	IfcLengthMeasure		Elevation in Z of the start point relative to the IfcAlignment coordinate system. NOTE It is strongly advised to not offset the IfcAlignment coordinate system from the project engineering coordinate system.	X
7	StartGradient	IfcRatioMeasure		Gradient of the tangent of the vertical segment at the start point. It is provided as a ratio measure. The ratio is percentage/100 (0.1 is equal to 10%). It has a theoretical range of -∞ < n < ∞ using a ratio measure. The equivalent range measured in degree is -90° < n < 90°. NOTE For practical application of start gradient, the range of the ratio measure should be within the limits of -1 ≤ n ≤ 1 (equivalent in degree -45° ≤ n ≤ 45°). However larger limits might apply for particular usages. Positive gradient means an increasing height at the start (or uphill), a negative gradient means decreasing height at the start (or downhill).	X
	ToVertical	IfcAlignment2DVertical @Segments	S[1:1]		X

Formal representations

XML Specification

 <xs:element name="IfcAlignment2DVerticalSegment" type="ifc:IfcAlignment2DVerticalSegment" abstract="true" substitutionGroup="ifc:IfcAlignment2DSegment" nillable="true"/>

 <xs:complexType name="IfcAlignment2DVerticalSegment" abstract="true">

  <xs:complexContent>

   <xs:extension base="ifc:IfcAlignment2DSegment">

    <xs:attribute name="StartDistAlong" type="ifc:IfcLengthMeasure" use="optional"/>

    <xs:attribute name="HorizontalLength" type="ifc:IfcPositiveLengthMeasure" use="optional"/>

    <xs:attribute name="StartHeight" type="ifc:IfcLengthMeasure" use="optional"/>

    <xs:attribute name="StartGradient" type="ifc:IfcRatioMeasure" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcAlignment2DVerticalSegment

 ABSTRACT SUPERTYPE OF(ONEOF(IfcAlignment2DVerSegCircularArc, IfcAlignment2DVerSegLine, IfcAlignment2DVerSegParabolicArc))

 SUBTYPE OF (IfcAlignment2DSegment);

  StartDistAlong : IfcLengthMeasure;

  HorizontalLength : IfcPositiveLengthMeasure;

  StartHeight : IfcLengthMeasure;

  StartGradient : IfcRatioMeasure;

 INVERSE

  ToVertical : SET [1:1] OF IfcAlignment2DVertical FOR Segments;

END_ENTITY;

 EXPRESS-G diagram