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提出一种三维参数化的系统模式，将参数化工作分为二维变量几何、扫描方向参数化及特征定位约束参数化３个相对独立的部分。针对反映三维参数化特点的定位约束参数化技术，提出用坐标系方式表示特征之间的定位约束关系，定义了所需的几种坐标系，分析了可能存在的约束关系类型，并从一般位置约束关系的分析入手，推导出相应的约束变换矩阵，拓宽了约束表示的覆盖域。还针对特征模型约束情况分析、判断和处理的需要，分析了各种约束类型的自由度亏损情况
A three-dimensional parametric system model is proposed, which divides the parameterization work into two relatively independent parts: the two-dimensional variable geometry, the parameterization of the scanning direction and the parameterization of the feature locating constraints. According to the parameterization technology of positioning constraints, which reflects the characteristics of three-dimensional parameterization, a coordinate system is used to represent the positioning constraints between the features. Several coordinate systems are defined and the types of constraints that may exist are analyzed. Starting with the analysis of the constraint relationship, the corresponding constraint transformation matrix is derived and the coverage of constraint representation is broadened. According to the need of analyzing, judging and dealing with the constraint of feature model, the paper also analyzes the loss of freedom degree of various constraint types