Within industrial contexts, a common view of the level of confidence needed in CAD data transfer processes may be expressed as "I don't mind if the [CAD data-transfer] algorithm sometimes has difficulties, provided I get a warning message that tells me something has gone wrong." A particularly annoying, even mystifying, CAD data exchange problem occurs in the so-called `round-trip' problem. There, an acceptable model is transferred from an originating system to a neutral format and then back to the original system, only to find that serious new flaws now appear in the model within the originating system. 1 Introduction The question of ensuring the integrity of data exchanges between companies is of great importance in Computer-Aided Design (CAD). Indeed, the problem is serious enough, and important enough, to have spawned a fairly large industry dedicated to its solution [5]. One integrity issue is the desire for consistency of topology and geometry data. Design models contain symbo...

In industrial design, the tool of choice for constructing surfaces that interpolate curves is the Boolean sum surface technique. However, if curves do not lie on constant parameter lines, reparametrizations will be needed, and this may introduce derivative discontinuities. A new technique which shows promise in overcoming this problem is described here. The method is based on describing the interpolation problem directly as a system of linear equations rather than as a curve-blending problem. The resulting system of equations is usually underdetermined and can be solved using numerical linear algebra methods without the a priori determination of certain parameters. The “free” parameters can be used to control the shape of the resulting surface. Two examples of the procedure are given.