IfcAlignment2DVerSegCircularArc

Item	SPF	XML	Change	Description
IFC4 ADD1 to IFC4x1
IfcAlignment2DVerSegCircularArc			ADDED

Semantic definitions at the entity

Entity definition

The vertical circular arc segment is defined as an arc using the inherited attributes from IfcAlignment2DVerticalSegment and the following additional curve parameters Radius as the radius of the circular arc, and IsConvex to indicate the whether the circular arc defines a sag or a crest.

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

R = signed Radius, 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 the centre of the circular arc:

center (distance along)		$s_{c} = s_{o} - R \times g_{0} \div \sqrt{1 + {g_{0}}^{2}}$
center (height)		$z_{c} = z_{0} + R \div \sqrt{{1 + g_{0}}^{2}}$

The following equations are used for any point along the circular arc:

at any point s₁ along the HorizontalLength
height (isConvex = True)		$z_{1} = z_{c} - \sqrt{R^{2} - {(s_{1} - s_{c})}^{2}}$
height (isConvex = False)		$z_{1} = z_{c} + \sqrt{R^{2} - {(s_{1} - s_{c})}^{2}}$
gradient		$g_{1} = - (s_{1} - s_{c}) / (z_{1} - z_{c})$

	start point provided by StartDistAlong and StartHeight instanteneous gradient provided by StartGradient, and length provided by HorizontalLength
Figure 211 — Alignment vertical arc segment convex

	start point provided by StartDistAlong and StartHeight instanteneous gradient provided by StartGradient, and length provided by HorizontalLength
Figure 212 — Alignment vertical arc segment concave

Attribute definitions

#	Attribute	Type	Cardinality	Description	B
8	Radius	IfcPositiveLengthMeasure	[1:1]	radius of the circular arc	X
9	IsConvex	IfcBoolean	[1:1]	orientation of the circular arc, convex (Boolean=”true”) means decreasing gradient along the arc at the beginning, concave (Boolean=”false”) means increasing gradient along the arc at the beginning	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.
IfcAlignment2DVerSegCircularArc
8	Radius	IfcPositiveLengthMeasure	[1:1]	radius of the circular arc	X
9	IsConvex	IfcBoolean	[1:1]	orientation of the circular arc, convex (Boolean=”true”) means decreasing gradient along the arc at the beginning, concave (Boolean=”false”) means increasing gradient along the arc at the beginning	X

Formal representations

XSD Specification

 <xs:element name="IfcAlignment2DVerSegCircularArc" type="ifc:IfcAlignment2DVerSegCircularArc" substitutionGroup="ifc:IfcAlignment2DVerticalSegment" nillable="true"/>

 <xs:complexType name="IfcAlignment2DVerSegCircularArc">

  <xs:complexContent>

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

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

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

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcAlignment2DVerSegCircularArc

 SUBTYPE OF (IfcAlignment2DVerticalSegment);

  Radius : IfcPositiveLengthMeasure;

  IsConvex : IfcBoolean;

END_ENTITY;

 EXPRESS-G diagram