IfcAlignment2DVerSegParabolicArc

Natural language names
Alignment 2D Vertical Segment Parabolic Arc
Change log
ItemSPFXMLChangeDescription
IFC4x1 Release Candidate 1
    IfcAlignment2DVerSegParabolicArcADDED
IFC4x1 Release Candidate 2
    IfcAlignment2DVerSegParabolicArc
      ToVerticalADDED
IFC4x1 Release Candidate 3
    IfcAlignment2DVerSegParabolicArc
      LayerAssignmentADDED
      StyledByItemADDED
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):

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

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 316 — Alignment vertical segment parabola convex

 

start point provided by StartDistAlong and StartHeight
instanteneous gradient provided by StartGradient,
and length provided by HorizontalLength

Figure 317 — Alignment vertical parabolic arc segment convex

 

 

start point provided by StartDistAlong and StartHeight
instanteneous gradient provided by StartGradient,
and length provided by HorizontalLength

Figure 317 — Alignment vertical parabolic arc segment concave

 
Attribute definitions
#AttributeTypeCardinalityDescription G
8ParabolaConstantIfcPositiveLengthMeasure 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
9IsConvexIfcBoolean Orientation of the parabolic arc, convex (Boolean=”true”) means decreasing gradient along the arc at the beginning such as at the crest of a hill, concave (Boolean=”false”) means increasing gradient along the arc at the beginning such as at the base of a valley.X
Inherited definitions from supertypes
Entity inheritance IfcAlignment2DVerticalSegment IfcAlignment2DSegment IfcGeometricRepresentationItem IfcRepresentationItem
Attribute inheritance
#AttributeTypeCardinalityDescriptionG
IfcRepresentationItem
LayerAssignmentIfcPresentationLayerAssignment
@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
StyledByItemIfcStyledItem
@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
1TangentialContinuityIfcBoolean? 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
2StartTagIfcLabel? Tag to annotate the start point of the alignment segment.X
3EndTagIfcLabel? Tag to annotate the end point of the alignment segment.X
IfcAlignment2DVerticalSegment
4StartDistAlongIfcLengthMeasure Distance along the horizontal alignment, measured along the IfcAlignment2DHorizontal given in the length unit of the global IfcUnitAssignment.X
5HorizontalLengthIfcPositiveLengthMeasure Length measured as distance along the horizontal alignment of the segment.X
6StartHeightIfcLengthMeasure 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
7StartGradientIfcRatioMeasure 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
ToVerticalIfcAlignment2DVertical
@Segments
S[1:1]X
IfcAlignment2DVerSegParabolicArc
8ParabolaConstantIfcPositiveLengthMeasure 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
9IsConvexIfcBoolean Orientation of the parabolic arc, convex (Boolean=”true”) means decreasing gradient along the arc at the beginning such as at the crest of a hill, concave (Boolean=”false”) means increasing gradient along the arc at the beginning such as at the base of a valley.X
Formal representations
XML 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;

Link to EXPRESS-G diagram EXPRESS-G diagram

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