Abstract: The extraction of feature lines is one of the key techniques in the optimization of the three-dimensional（3D） surface mesh.The major objective of this paper is to extract feature lines from the 3D surfaces stored in stereolithography（STL） files using the computer-aided design（CAD）.An auto-adaptive method is developed to establish the threshold for feature line extraction with the statistical analysis of dihedral angles，and combined with the perimeter ratio to effectively extract 3D feature lines.Numerical experiments demonstrate that the feature lines extracted using the method proposed in this paper retain the original 3D features.

Key words: STL files, feature line, dihedral angle

摘要： 特征线的提取是表面网格优化的关键技术之一。本文的主要目的是从CAD下的STL（Stereolithography）文件中提取3D表面网格的特征线。通过对二面角进行统计分析，给出了一种自适应获取特征线阀值的方法，并结合周长比值法有效地提取3D表面网格的特征线。实验表明这些特征线能很好地保持3D表面的轮廓。

关键词: STL文件, 特征线, 二面角