# NAME

GDX_OFFSET_SURFACE - Offset Surface

# GENERAL DESCRIPTION

A GDX Offset Surface represents the offset of a GDX surface entity. This entity is defined in terms of a base surface to be offset and an offset distance. The direction to offset any point on the base surface is determined by crossing the vector obtained by evaluating the partial derivative of the surface with respect to the u direction with the vector obtained by evaluating the partial derivative of the surface with respect to the v direction. the tangent to the base surface at that point.

# DDF SPECIFICATION

    entity 20:0  GDX_OFFSET_SURFACE   "Offset Surface" {

    double
    OFF_DISTANCE;

    ptr
    SURFACE
    reftype = (P_SURFS);

    };

# FIELD DESCRIPTIONS

OFF_DISTANCE

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

SURFACE

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

GDX_NURB_SURF
GDX_SPLINE_SURF
GDX_RULED_SURF
GDX_REV_SURF
GDX_EXT_SURF
GDX_PLANE
GDX_CYLINDER
GDX_CONE
GDX_SPHERE
GDX_TORUS
GDX_OFFSET_SURF
GDX_RECT_TRIM_SURF

# PARAMETERIZATION

The parameterization is the same as that used for the IGES Offset Surface Entity (Type 140) and can be found in Section 4.28 of The Initial Graphics Exchange Specification (IGES) Version 5.2.

# PARAMETRIC RANGE

The GDX Offset Surface is defined over the following parametric range: u0 <= u <= u1 v0 <= v <= v1

       where u0 and u1 are u bounds of the base surface and v0 and v1
       are v bounds of the base surface.

# RESTRICTIONS

None.