# NAME

GDX_OFFSET_CURVE - Offset Curve

# GENERAL DESCRIPTION

A GDX Offset Curve represents the offset of a GDX curve entity. This entity is defined in terms of a base curve to be offset, an offset distance, and a normal vector. The direction to offset any point on the base curve is determined by crossing the normal vector with the tangent to the base curve at that point.

# DDF SPECIFICATION

    entity 6:0  GDX_OFFSET_CURVE   "Offset Curve" {

    double
    PLANE_NORMAL[3];

    double
    OFF_DISTANCE;

    double
    T0;

    double
    T1;

    ptr
    CURVE
    reftype = (P_CURVES);

    };

# FIELD DESCRIPTIONS

PLANE_NORMAL

The 3D coefficients of the normal vector to the plane from which to offset that base curve. This vector should not be parallel to the tangent of the base curve to be offset at any point along the base curve.

OFF_DISTANCE

The GDX Offset Curve offset distance. This distance may be positive, negative, or 0.0.

T0

The starting parameter of the GDX Offset Curve.

T1

The ending parameter of the GDX Offset Curve.

CURVE

The database pointer of the GDX curve to be offset. The allowable GDX entity type/forms consists of the parametrically defined GDX curve entities as defined by the P_CURVES ptrlist variable in gdx.ddf. For reference, these entities are:

GDX_CONIC
GDX_NURB_CURVE
GDX_ARC
GDX_SPLINE_CURVE
GDX_POLYLINE
GDX_COMP_CURVE
GDX_OFFSET_CURVE
GDX_TRIM_CURVE

# PARAMETERIZATION

The parameterization is the same as that used for the IGES Offset Curve Entity (Type 130) and can be found in Section 4.23 of The Initial Graphics Exchange Specification (IGES) Version 5.2.

# PARAMETRIC RANGE

The GDX Offset Curve is defined over the following parametric range: T0 <= u <= T1 Note that T0 and T1 must be in the domain of the base curve.

# RESTRICTIONS

The curve to be offset must be tangent continuous at all points. For example single point polylines and closed polylines are not valid curves to be offset.