Construction of 3D Constraint Models for History-Independent Modeling

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.