中文摘要：

由于与历史无关的造型系统中约束模型多处于欠约束状态，使求解结果往往不能很好地符合设计意图，为此提出一种基于虚几何元素的约束模型构建方法．该方法根据输入约束的方向特性创建虚几何元素，并将这些约束转换为实体几何元素、虚几何元素间的结构约束和尺寸约束，从而构建基本约束模型；在此基础上，通过几何元素的剩余自由度分析增补相应的几何约束，使约束模型更完备，求解结果更合理．文中方法已在原型系统InteModel中实现，并通过实例验证了其正确性和有效性．

英文摘要：

In history-independent modeling system, the constraint model is often in under-constraint status, which may make the resolving result not meet the design intention well. A new approach based on virtual geometric elements is proposed to construct a constraint model, in which virtual geometric elements are defined according to the directional characteristic of input constraints. And then such constraints are converted into structure and dimension constraints among existing geometric elements and virtual geometric elements. In addition, the remaining degrees of freedom （DOFs） of such geometric elements are analyzed, and the complementary constraints are appended so that the constraint model is complete and the resolving results satisfy the design intentions better. The proposed method has been implemented and validated by two examples in a prototype system named InteModel.