# 8.9.3.49 IfcPointByDistanceExpression

## 8.9.3.49.1 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.

## 8.9.3.49.5 Formal representation

ENTITY IfcPointByDistanceExpression
SUBTYPE OF (IfcPoint);
DistanceAlong : IfcCurveMeasureSelect;
OffsetLateral : OPTIONAL IfcLengthMeasure;
OffsetVertical : OPTIONAL IfcLengthMeasure;
OffsetLongitudinal : OPTIONAL IfcLengthMeasure;
BasisCurve : IfcCurve;
END_ENTITY;