IfcAlignment2DVerSegParabolicArc

Item	SPF	XML	Change	Description
IFC4 ADD1 to IFC4x1
IfcAlignment2DVerSegParabolicArc			ADDED

Semantic definitions at the entity

Entity definition

The vertical parabolic segment is defined as a parabola using the inherited attributes from IfcAlignment2DVerticalSegment and the following additional curve parameters ParabolaConstant as the minimum radius of the parabolic arc at its apex, and IsConvex to indicate the whether the parabolic arc defined a sag or a crest.

The parabolic arc is described by (see figure 1):

R = signed ParabolaConstant, if IsConvex = true, then +R, if IsConvex = false, then -R as length measure
s₀ = StartDistAlong as length measure
z₀ = StartHeight as length measure
g₀ = StartGradient as ratio measure

The following equations are used for any point along the parabola:

at any point s₁ along the HorizontalLength
the gradient g₁ = (s₁-s₀) / R + g₀
the height z₁ = (s₁-s₀) * (g₁+g₀)/2 + z₀

Legend:
red: the parabolic curve with start point and calculated end point used as an vertical alignment
yellow: the underlying unbounded parabola definition
blue: the minimum circle defined by the parabola constant agreeing to the "is convex" fag, the constant, and the start gradient

Figure 214 — Alignment vertical segment parabola convex

	start point provided by StartDistAlong and StartHeight instanteneous gradient provided by StartGradient, and length provided by HorizontalLength
Figure 215 — Alignment vertical parabolic arc segment convex

	start point provided by StartDistAlong and StartHeight instanteneous gradient provided by StartGradient, and length provided by HorizontalLength
Figure 215 — Alignment vertical parabolic arc segment concave

Attribute definitions

#	Attribute	Type	Cardinality	Description	B
8	ParabolaConstant	IfcPositiveLengthMeasure	[1:1]	Parabola constant (determining the “steepness” of the parabola). The parabola constant is provided by the “minimum parabola radius”, the true radius of a parabola at its vertical axis (the zero-gradient point of the parabola). The minimum radius is twice the focal length of the parabola (the distance between the focal point and the vertex).	X
9	IsConvex	IfcBoolean	[1:1]	Orientation of the parabolic arc, convex (Boolean=”true”) means that the minimum radius is the distance between the vertex and the center point along the positive direction of the vertical axis, and concave (Boolean=”false”) means along the negative direction of the vertical axis. NOTE&bsp; Convex normally stands for a sag or valley and concave for a crest or hill	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	B
IfcAlignment2DSegment
1	TangentialContinuity	IfcBoolean	[0:1]	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	[0:1]	Tag to annotate the start point of the alignment segment.	X
3	EndTag	IfcLabel	[0:1]	Tag to annotate the end point of the alignment segment.	X
IfcAlignment2DVerticalSegment
4	StartDistAlong	IfcLengthMeasure	[1:1]	Distance along the horizontal alignment, measured along the IfcAlignment2DHorizontal given in the length unit of the global IfcUnitAssignment.	X
5	HorizontalLength	IfcPositiveLengthMeasure	[1:1]	Length measured as distance along the horizontal alignment of the segment.	X
6	StartHeight	IfcLengthMeasure	[1:1]	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	[1:1]	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]	Link to the IfcAlignment2DVertical to which this vertical segment belongs.
IfcAlignment2DVerSegParabolicArc
8	ParabolaConstant	IfcPositiveLengthMeasure	[1:1]	Parabola constant (determining the “steepness” of the parabola). The parabola constant is provided by the “minimum parabola radius”, the true radius of a parabola at its vertical axis (the zero-gradient point of the parabola). The minimum radius is twice the focal length of the parabola (the distance between the focal point and the vertex).	X
9	IsConvex	IfcBoolean	[1:1]	Orientation of the parabolic arc, convex (Boolean=”true”) means that the minimum radius is the distance between the vertex and the center point along the positive direction of the vertical axis, and concave (Boolean=”false”) means along the negative direction of the vertical axis. NOTE&bsp; Convex normally stands for a sag or valley and concave for a crest or hill	X

Formal representations

XSD Specification

 <xs:element name="IfcAlignment2DVerSegParabolicArc" type="ifc:IfcAlignment2DVerSegParabolicArc" substitutionGroup="ifc:IfcAlignment2DVerticalSegment" nillable="true"/>

 <xs:complexType name="IfcAlignment2DVerSegParabolicArc">

  <xs:complexContent>

   <xs:extension base="ifc:IfcAlignment2DVerticalSegment">

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

    <xs:attribute name="IsConvex" type="ifc:IfcBoolean" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcAlignment2DVerSegParabolicArc

 SUBTYPE OF (IfcAlignment2DVerticalSegment);

  ParabolaConstant : IfcPositiveLengthMeasure;

  IsConvex : IfcBoolean;

END_ENTITY;

 EXPRESS-G diagram