added |

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.

# | Attribute | Type | Description |
---|---|---|---|

IfcRepresentationItem | |||

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. > 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. | |

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. > IFC2x3 CHANGE The inverse attribute StyledByItem has been added. | |

IfcGeometricRepresentationItem | |||

IfcPoint | |||

IfcPointByDistanceExpression | |||

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 | |

Dim | INVALID |

ENTITY IfcPointByDistanceExpression SUBTYPE OF (IfcPoint); DistanceAlong : IfcCurveMeasureSelect; OffsetLateral : OPTIONAL IfcLengthMeasure; OffsetVertical : OPTIONAL IfcLengthMeasure; OffsetLongitudinal : OPTIONAL IfcLengthMeasure; BasisCurve : IfcCurve; DERIVE Dim : IfcDimensionCount := BasisCurve.Dim; END_ENTITY;