IFC (IFC4X3_TC1) IfcPointByDistanceExpression Semantic definition

An IfcPointByDistanceExpression describes a point relative to a basis curve according to distance along the basis curve. The offsets default to the initial context of the curve relative to it's tangent either specified in IfcProduct.Placement or in the case of a segmented curve to the IfcCurveSegment StartPlacement where the values correspond to the following:

  • lateral to the basis curve
  • offset vertical to the basis curve
  • optional additional offset parallel to the basis curve that may be used to address locations otherwise unreachable where the basis curve is tangentially discontinuous. Entity inheritance Attributes

# Attribute Type Description
IfcRepresentationItem (2)
LayerAssignment SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems

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.

StyledByItem SET [0:1] OF IfcStyledItem FOR Item

Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.

IfcPoint (1)
* Dim IfcDimensionCount

This attribute is formally derived.


The space dimensionality of this abstract class, handled by a function specific for concrete subtypes. Determined by the number of coordinate components in case of IfcCartesianPoint or by the dimensionality of the basis curve or surface in other cases.

Click to show 3 hidden inherited attributes Click to hide 3 inherited attributes
IfcPointByDistanceExpression (5)
1 DistanceAlong IfcCurveMeasureSelect

The distance along the basis curve measured as either a IfcLengthMeasure or IfcParameterValue.

2 OffsetLateral OPTIONAL IfcLengthMeasure

Default offset horizontally is measured perpendicular to the basis curve, where positive values indicate to the left of the basis curve as facing in the positive parametrization direction of the basis curve, and negative values indicate to the right. If DistanceAlong coincides with a point of tangential discontinuity (within precision limits), then the tangent of the previous segment governs.

3 OffsetVertical OPTIONAL IfcLengthMeasure

Default offset vertical to the basis curve where positive values indicate perpendicular to the tangent at DistanceAlong in the plane of the tangent perpendicular to the global XY plane.

4 OffsetLongitudinal OPTIONAL IfcLengthMeasure

Offset parallel to the basis curve after applying DistanceAlong, OffsetLateral, and OffsetVertical to reach locations for the case of a tangentially discontinuous basis curve.

5 BasisCurve IfcCurve

No description available.

Table Examples Formal representation

ENTITY IfcPointByDistanceExpression
 SUBTYPE OF (IfcPoint);
	DistanceAlong : IfcCurveMeasureSelect;
	OffsetLateral : OPTIONAL IfcLengthMeasure;
	OffsetVertical : OPTIONAL IfcLengthMeasure;
	OffsetLongitudinal : OPTIONAL IfcLengthMeasure;
	BasisCurve : IfcCurve;
END_ENTITY; References Changelog IFC4.3_TC1

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