SYSTEM OF RELATIONAL ENTITIES FOR OBJECT-ORIENTED COMPUTER-AIDED GEOMETRIC DESIGN

Geometric objects including points, lines, curves, surfaces and solids are defined and constructed in a system which retains and utilizes relationships and dependencies between objects in a directed graph (digraph) data structure. The primary advantage is automatic updating of the model, preserving dependencies, when an underlying object is changed. Multiple types of parametric curves and surfaces and multiple levels of dependency are easily supported through a recursive program structure. Difficulties of surface-surface intersection and trimming are largely avoided by provision of novel entities which permit construction of accurate and durable joins between surface objects. An example model (FIG. 27 ) of a sailing yacht design illustrates six surface objects of several types with the defined dependency relationships. The hull 271, deck 272, cabin forward 273, cabin side 274, cabin aft 275 and cabin top 276 surfaces intersect at joins 278, 279 which are accurate and durable. The connectivity at the joins and the relative positioning of the surfaces are automatically preserved as the model is updated by changing one of the surfaces.