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ISO 10303-42:2003 specifies the resource constructs for the explicit geometric and topological representation of the shape of a product. The scope is determined by the requirements for the explicit representation of an ideal product model; tolerances and implicit forms of representation in terms of features are out of scope. The geometry in clause 4 and the topology in clause 5 are available for use independently and are also extensively used by the various forms of geometric shape model in clause 6.

In addition, ISO 10303-42:2003 specifies specialisations of the concepts of representation where the elements of representation are geometric.

The following are within the scope of the geometry schema:

• definition of points, vectors, parametric curves and parametric surfaces;
• definition of finite volumes with internal parametrisation;
• definition of transformation operators;
• points defined directly by their coordinate values or in terms of the parameters of an existing curve or surface;
• definition of conic curves and elementary surfaces;
• definition of curves defined on a parametric surface;
• definition of general parametric spline curves, surfaces and volumes;
• definition of point, curve and surface replicas;
• definition of offset curves and surfaces;
• definition of intersection curves.

The following are outside the scope of ISO 10303-42:2003:

• all other forms of procedurally defined curves and surfaces;
• curves and surfaces which do not have a parametric form of representation;
• any form of explicit representation of a ruled surface.

NOTE For a ruled surface the geometry is critically dependent upon the parametrisation of the boundary curves and the method of associating pairs of points on the two curves. A ruled surface with B-spline boundary curves can however be exactly represented by the B-spline surface entity.