Chapter 3 - The Cambridge Connection: Foundations of Modern CAD

Before diving into the individual stories of CAD pioneers, it’s worth understanding the deeper technological foundations that shaped the evolution of modern CAD systems. The geometric modeling capabilities behind today’s software can be traced back to foundational research in solid modeling that began in the 1960s, particularly at the University of Cambridge’s Computer Laboratory. Under the direction of Professor Maurice Wilkes, Charles Lang established a CAD research group in 1965 that became a crucible of innovation in computational geometry and computer graphics.

Early breakthroughs emerged with the BUILD boundary representation modeler, developed by Ian Braid starting in 1969 under Lang’s supervision. BUILD tackled challenges in solid modeling—like exact surface-surface intersections—that others avoided through faceting. Alan Grayer joined in 1971, focusing on algorithms for machining prismatic parts modeled in BUILD, leading to one of the earliest integrations of CAD with CAM.

This pioneering work laid the groundwork for ROMULUS, a commercial solid modeling kernel developed at Shape Data Ltd., a company founded in 1974 by Braid, Grayer, Lang, and Peter Veenman. ROMULUS was released commercially in 1978 and became the kernel behind systems like HP’s ME30. In 1985, Shape Data began development of Parasolid as a more advanced successor to ROMULUS, with an improved architecture.

Later that year, Ian Braid, Alan Grayer, and Charles Lang left Shape Data to co-found Three-Space Ltd, collaborating with Spatial Technology Inc., a company founded by Dick Sowar in Colorado. Together, they developed ACIS, a completely new kernel released in 1989, known for its support for both manifold and non-manifold modeling, wires, sheets, and precision modeling techniques.  There is a popular story that ACIS' name was derived from its founders, "Alan, Charles, and Ian's System" and there is another that claims they credited the obscure Greek mythology around Acis in Ovid's Metamorphoses. I guess you can choose which one you prefer. Either way, the often-simplified notion that Parasolid and ACIS were developed independently misses the continuity: both kernels trace directly back to the Cambridge team that pioneered boundary representation modeling, and both were led or heavily influenced by the same core individuals.

While Parasolid and ACIS implement similar mathematical principles—such as B-rep, constructive solid geometry (CSG), and separation of geometry from topology—they are distinct codebases. Parasolid was originally written in FORTRAN and C before transitioning to C++, whereas ACIS was developed in C from the outset with object-oriented extensions. Cambridge’s UK legacy in geometric modeling, much like MIT’s in the U.S. PLM scene (see this article) in Cambridge, MA, continues to echo in nearly every major CAD system in use today.