Representation, evaluation and editing of feature-based and constraint-based design

This thesis investigates a general and systematic approach to feature-based and constraint-based design. We combine feature-based design and constraint-based design by globally decomposing a design into a sequence of feature attachments and locally defining and positioning each feature by constraints. Analogous to the concept of high-level programming languages, we formalize a layered design model that eliminates the dependency of a design representation on a solid modeler. With this design model, design intent, such as feature descriptions and constraints, is stored in an unevaluated, modeler-independent design representation while the geometry to which it corresponds is stored in an evaluated, modeler-dependent design representation. The separation essentially relies on a naming and matching schema that converts between a geometric reference and a generic name, and a design compiler that automatically instantiates the unevaluated design representation to an evaluated design representation with respect to a solid modeler. The geometric references for defining feature attributes and constraints are recorded with their generic names in the unevaluated design representation. We propose several techniques for naming geometric entities unambiguously. The design compilation or instantiation involves remapping a generic name back to a geometric reference in the selected geometric modeler, solving constraints and implementing feature operations or attachments. Instead of developing a constraint solver for this design compiler, we use an independent and general solver. Feature attachment operations are different from classical Boolean operations in solid modeling. However, we provide a semantics for them that is based on existing operations in solid modeling. The layered design model allows users to edit archived conceptual designs to derive new designs quickly. We investigate the coordination of later features in the unevaluated and modeler-independent representation when a feature is edited and provide a method for editing feature-based and constraint-based design. We also discuss how to extend this work to a commercial feature-based and constraint-based CAD system