Abstract: This paper presents a precise clipping algorithm for 3D Triangulated Irregular Network（TIN） based on constrained Delaunay triangulation.Combined with the generation of TIN，firstly the algorithm projects the TIN data onto the two-dimensional plane，and inserts the edges of clipping polygon into TIN，and uses E-T topology to delete external triangles，lastly uses E-P topology to interpolate vertex elevation of clipping polygon，and generates the new TIN model after clipping.The experiment results gained by several clippings to 3D TIN models with different scales，show that the 2D projection has raised the efficiency of the algorithm evidently.The algorithm can be implemented by programs easily，and can accord with requirements of the project.

Key words: constrained Delaunay triangulation, clipping polygon, topology, 2D projection

摘要： 给出了一种基于约束Delaunay三角剖分的三维不规则三角网格的精确裁剪算法。算法结合TIN数据的生成特点，首先将TIN投影到二维平面，然后利用约束Delaunay三角剖分把裁剪多边形的每条边嵌入三角网中，再利用边-三角形的拓扑关系删除裁剪多边形外部多余三角形，最后利用边-点的拓扑关系对裁剪多边形顶点高程进行插值，使生成裁剪后的TIN模型。对不同复杂程度的三维TIN模型进行裁剪实验，发现二维投影策略极大地提高了三维TIN裁剪效率。算法的程序实现简单，且符合工程需求。

关键词: 约束Delaunay三角剖分, 裁剪多边形, 拓扑关系, 二维投影