A Hybrid Non-strict Implicit Constraints Solving Algorithm

2D sketch is the basis for 3D features. Constructive constraints are usually not given evidently. When a 3D feature is transferred to another CAD system, this kind of constraints is lost. Or when a sketch is drawn with errors, the subsequent parametric reasoning can not process smoothly. This paper proposed a general algorithm for the recognization and correction of these non-strict implicit constraints by combing the advantages of graph based approach and rule based approach. The implicit constraints are described by a constraint graph . Strict constraints and non-strict constraints within an error threshold are marked separately. All approximate constraints are predigested to general biting points. Sets of processing rules are formulated elaborately to assure an optimized result. Experiment results show this algorithm is time efficient and widely applicable in most engineering drawings.