一种以特征线为中心的曲面特征表示方法

由于自由曲面特征形状复杂多样，难以有效地进行参数化表示．本文提出了一种以特征线为中心的曲面特征层次参数化的表示方法．该方法将特征线作为曲面构建的基本单元，将特征线划分为几何层、约束层、语法层和语义层，利用特征线信息对曲面特征进行参数分层，实现曲面特征的整体形状和局部形状的层次控制；在参数化表示上，按不同自由度分为半自由和完全自由曲面特征，并对曲面特征进行了统一的定义表示．实验结果表明，本文方法能够表达多种形状的自由曲面，在高层语义参数层面上方便地编辑曲面特征，是一种有效的曲面特征表示方法．

A representation of freeform features based on characteristic curves

Owing to the diversity and complexity surface features and express their shapes effectively of freeform surface shapes, it is difficult to parameterize A parametric approach for layering freeform surface features is proposed based on characteristic curves. A characteristic curve is a key element and is regarded as the basic unit for building surface shapes. A characteristic curve can be divided into four levels, comprising, from the lowest to the highest level, geometry, constraints, grammar, and semantics. The information is used to layer the parameters of a freeform surface feature so that the global and local shapes of the surface feature can easily be manipulated by the layered parameters. The global shape is controlled by the high parameters between multi characteristic curves, while the local shape is manipulated by these parameters with a single curve. According to the degrees of the surface and its parametric representation, freeform surface features can be divided into two types： semi-freeform and fully freeform. Then, the freeform surface feature is combined in the representation. Using various examples we show that the proposed method can fully express complex surfaces and is effective in defining freeform surface features, making it convenient for semantic parameters. Moreover, it provides an efficient way designers to edit freeform features from higher-level of representing freeform surface features.