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# IfcSegmentedReferenceCurve
-The _IfcSegmentedReferenceCurve_ is a curve defined in the linear parameter space of its base curve that is set in the attribute _BaseCurve_. The base curve provides a basis for the positioning of the collection of _IfcCurveSegment_ occurrences. A deviating explicit position of a curve segment (_IfcCurveSegment_.Placement) from the axis of the base curve produces a superelevation i.e. depression or elevation from the axis of the base curve. The superelevation rate of change is directly proportionate to the curve segment parent curve curvature gradient equation (_IfcCurveSegment_._ParentCurve_) in the linear parameter space of the base curve. If no deviation in the position of the curve segment to the base curve axis is specified, the axes (Axis and RefDirection) directions of _IfcAxis2Placement_ are interpolated between the initial curve segment placement and the placement of the subsequent curve segment.
+The _IfcSegmentedReferenceCurve_ is a curve defined in the linear parameter space of its base curve that is set in the attribute _BaseCurve_. The base curve provides a basis for the positioning of the collection of _IfcCurveSegment_ occurrences. A deviating explicit position of a curve segment (_IfcCurveSegment.Placement_) from the axis of the basis curve produces a superelevation (i.e. depression or elevation from the axis of the base curve). The deviating elevation is defined by the _IfcCurveSegment.ParentCurve_ in the linear parameter space of the base curve. If no deviation in the position of the curve segment to the base curve axis is specified, the axes (_Axis_ and _RefDirection_) directions of _IfcAxis2Placement_ are interpolated between the initial curve segment placement and the placement of the subsequent curve segment.
-The parametrization of _IfcSegmentedReferenceCurve_ is based on the parametrization of _BaseCurve_ and is not altered by the _Segments_.
+The parameterization of _IfcSegmentedReferenceCurve_ is based on the parameterization of the _BaseCurve_ and is not altered by the _Segments_.
-Figure 1 shows a cross section of a _IfcSegmentedReferenceCurve_ usage for an alignmnent representation featuring cant
+Figure 1 shows a cross section of a _IfcSegmentedReferenceCurve_ usage for an alignment representation featuring cant with rotation about the low rail and varying superelevation.
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+
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+Figure 1 — use of a segmented reference curve on a cant segment based on a gradient curve.
+
+Figure 2 shows a cross section of a _IfcSegmentedReferenceCurve_ usage for an alignment representation feature cant with rotation about the track centerline with no deviating position.
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+
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+Figure 2 — use of a segmented reference curve on a cant segment based on a gradient curve with rotation about track centerline and no superelevation.
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+Informally, a _IfcSegmentedReferenceCurve_ is a curve defined in a “horizontal distance along base curve, deviating elevation” coordinate system. The _IfcCurveSegment.ParentCurve_ defines the change in cross slope between rail heads over the length of the segment. When the _IfcCurveSegment.Placement.Location_ differs from the _IfcCurveSegmentPlacement.Location_ of the next segment (or the _IfcSegmentedReferenceCurve.EndPoint_ for the last segment, if specified), the _IfcCurveSegment.ParentCurve_ also defines the deviating elevation. If the _IfcCurveSegment.Placement.Location_ is the same as for the start of the next segment, the deviating elevation along the length of the segment is constant.
+
+The evaluation of a _IfcCurveSegment_ that is part of a _IfcSegmentedReferenceCurve_ is illustrated by the file in the Examples section below.
## Attributes