IfcOffsetCurve2D

Definition from ISO/CD 10303-42:1992: An offset curve 2d (IfcOffsetCurve2d) is a curve at a constant distance from a basis curve in two-dimensional space. This entity defines a simple plane-offset curve by offsetting by distance along the normal to basis curve in the plane of basis curve. The underlying curve shall have a well-defined tangent direction at every point. In the case of a composite curve, the transition code between each segment shall be cont same gradient or cont same gradient same curvature.

> NOTE: The offset curve 2d may differ in nature from the basis curve; the offset of a non self- intersecting curve can be self-intersecting. Care should be taken to ensure that the offset to a continuous curve does not become discontinuous.

The offset curve 2d takes its parameterization from the basis curve. The offset curve 2d is parameterized as

where T is the unit tangent vector to the basis curve C(u) at parameter value u, and d is distance. The underlying curve shall be two-dimensional.

> NOTE Corresponding STEP entity: offset_curve_2d, Please refer to ISO/IS 10303-42:1994, p.65 for the final definition of the formal standard.

> HISTORY New entity in IFC Release 2.x

EXPRESS specification:

ENTITY IfcOffsetCurve2D
SUBTYPE OF ( | IfcCurve);
BasisCurve | : | IfcCurve;
Distance | : | IfcLengthMeasure;
SelfIntersect | : | LOGICAL;
WHERE
WR1 | : | BasisCurve.Dim = 2;
END_ENTITY;

Attribute definitions:

BasisCurve | : | The curve that is being offset.
Distance | : | The distance of the offset curve from the basis curve. distance may be positive, negative or zero. A positive value of distance defines an offset in the direction which is normal to the curve in the sense of an anti-clockwise rotation through 90 degrees from the tangent vector T at the given point. (This is in the direction of orthogonal complement(T).)
SelfIntersect | : | An indication of whether the offset curve self-intersects; this is for information only.

Formal Propositions:

WR1 | : | The underlying curve shall be defined in two-dimensional space.

Inheritance graph

ENTITY IfcOffsetCurve2D;
ENTITY IfcRepresentationItem;
INVERSE
LayerAssignments | : | SET OF IfcPresentationLayerAssignment FOR AssignedItems;
StyledByItem | : | SET [0:1] OF IfcStyledItem FOR Item;
ENTITY IfcGeometricRepresentationItem;
ENTITY IfcCurve;
DERIVE
Dim | : | IfcDimensionCount := IfcCurveDim(SELF);
ENTITY IfcOffsetCurve2D;
BasisCurve | : | IfcCurve;
Distance | : | IfcLengthMeasure;
SelfIntersect | : | LOGICAL;
END_ENTITY;