Design And Implementation Of Feature-Management Modules In FCAD

The passing several years saw the fast development of CAD techniques as well as the upgrading of the contemporary CAD systems. Newest CAD systems always have more convenient interfaces, shorter reacting time and more powerful functions. In order to provide a more efficient CAD system, we re-designed FCAD in base of our latest application, GS-CAD, from last year.In this article, the author presents how several important modules in FCAD system are designed and implemented.Firstly, I introduce the main structure of FCAD system. The hierarchy and relationships of all modules in FCAD and functions of each module are described.Our FCAD system is a history-based parameterized solid modeling system. In this kind of CAD systems, the module to manage features is most important. This author mainly presents methods to design and implement the feature-management module in FCAD. First I explain some primitive concepts in our system, such as entity, feature, operating history, and how to define their relationships. Then I present in detail how to implement some necessary functions, such as creating, deleting, modifying, roll-backing, suppressing (un-suppressing) a feature. We also have designed the mechanism to achieve the undo and redo functions, which are very important for a part-edit process. All these functions are based on our history-based method. Last, in order to decrease the cost of regeneration of a model, I take snapshots for operations at intervals. When regenerating a model, I replace the current model with the latest valid snapshot, and then redo all operations after that operation.Another important part in a CAD system, naming mechanism is also presented. We used a hybrid local naming method. Our method is a face-based naming mechanism. The name of a face is consisted of an operator ID, an inner ID and an array of references of its neighbor faces. When merging or splitting a face, we give some special rules to name the new faces. These rules make face-mapping simpler. Naming of edges and vertex are based on the naming effaces.Functions to save or load a part are also very important for a CAD system. In the end of the article, the author presents the method to save/load a part too. We have improved the serializing methods used in MFC to finish saving and loading a part inFCAD. In our method, we handle successfully pointers of pure virtual classes and instants with more than one reference.