Exchange of Curve and Surface Data

Abstract

In the previous chapter the industrial and commercial necessity to exchange product definition data has been described, as well as some of the problems encountered with using current neutral file specifications for this purpose. Many of the least tractable problems are encountered when attempting to communicate data concerned with the description of complex curves and surfaces in 3D space. The basic source of all these problems is the wide variety of definition formats used for curve and surface data by different CAD/CAM systems. In the past analytic, parametric and procedural forms have all been used for the definitions of curves and surfaces in CAD/CAM systems but parametric forms are by far the most popular. In some cases it is possible to perform, theoretically at least, an exact mathematical conversion between two different forms of representation, algorithms for this purpose are described in Chapter 4. In far too many cases no exact conversion is possible and the best that can be achieved is to produce some form of ‘good’ approximation to the original data which is acceptable to the receiving system. Some useful approximation algorithms which preserve as much as possible of the geometric intent of the original design are described in Chapters 5 and 6.