Visual, Interactive 3D Spatial Grammars in CAD for Computational Design Synthesis
Author: Hoisl, Frank Rainer
Supervisor: Prof. Kristina Shea
Institution: Technische Universität München
While Computer-Aided Design (CAD) has made significant progress since its inception, CAD tools are still used primarily for the creation, modification and documentation of designs rather than as ‘active’ partners in the design process. Spatial grammars are an approach for design synthesis having the potential to computationally support the human designer. They provide a method for rule-based, generative shape design but have yet to find general application within CAD systems. While many spatial grammars exist on paper, only a few have been computationally implemented to date. This is especially the case for threedimensional systems. Most spatial grammars are hard-coded, i.e., once implemented, the vocabulary and rules cannot be changed without re-programming. This work presents a new approach for creating a general three-dimensional spatial grammar system based on mechanical engineering CAD that enables visual, interactive definition and application of grammar rules for computational design synthesis. The method is based on a set grammar that uses a set of parameterized primitives and supports the definition of nonparametric and parametric rules, as well as their automatic application. It comprises a method for the automatic matching of the left hand side of a rule in a current working shape, including
defining parametric relations. Enhancements to the set grammar approach enable the use of Boolean operations, sweeping objects and three-dimensional labels to significantly increase the expressiveness of the geometry that can be generated with regard to mechanical engineering solutions. In addition to parametric relations and labels that are used as instruments to embed constraints in the rules, a collision detection mechanism is introduced to prevent generation of overlapping parts and to constrain the possible design space. A prototype implementation based on an open-source 3D modeling kernel and CAD system is presented and used to illustrate the approach through several mechanical engineering design examples such as the generation of vehicle wheel rims, robot arm concepts or gear systems. The main contribution that results from this approach is that instead of being exclusively created for a specific example or domain, the software prototype provides a flexible platform supporting designers with visual, interactive definition and application of their own spatial grammar rules in a familiar CAD environment without programming. It puts the creation and use of three-dimensional spatial grammars on a more general level and enables their usability in mechanical engineering CAD systems to provide for more ‘active’ support of the engineering designer.