CAD SURFACE DATA EXCHANGE USING STEP

In 1991, the International Standards Organisation will publicly present a technical proposal for a part of Version 1.0 of STEP, the international standard for external representation of product data. STEP provides advanced methods for product-model specification and for the realization of high-quality data-exchange processes. The main obstacles to the integration of CAD/CAM systems are the incompatibility of the individual data-type domains and the multiplicity of implementations of certain entities. The paper demonstrates that the latter problem can be ameliorated via the proposed STEP specification. This is illustrated with reference to B-spline curves and B-spline surfaces. The geometry Part of STEP is briefly outlined, and the definition of B-spline entities in the EXPRESS language is given. It is shown how these entities meet the requirements for STEP data exchange. The multipurpose character of STEP B-splines is illustrated with numerical examples.