| 摘要 |
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 o f novel entities which permit construction of accurate and durable joins between surface objects. An example model of a sailing yac ht 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 mode l is updated by changing one of the surfaces.
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