Only vertex chain code can be applied to triangular grids, but it has defect in angle adjacent expression. Aimed at the problem of object border representation in triangular grid, three novel chain codes were proposed and compared in character and performance. Firstly, Freeman chain code was extended to triangular grids. For two different triangular elements, the corresponding 12-direction Freeman chain code encoding rules were designed respectively. Secondly, based on the relative direction changes of the contour, the relative direction chain code was proposed. Finally, the edge chain code could be obtained by differentiating the combinations of edges number and internal grids number of the boundary grids. The geometric properties, expressive abilities and compression ratios of three novel chain codes were compared and analyzed. Experiments show that the proposed methods can accurately and completely realize the shape boundary expression of triangular grids. Among them, edge chain owns the best performance, the average code number per grid is 1, and compression ratio can reach 0.75.

目前可以应用于三角形网格的链码方法只有顶点链, 而它对角相邻情况的表达存在缺陷, 针对此问题, 提出3种链码方法, 并进行特性分析和性能比较。首先将Freeman链码扩展应用到三角形网格, 根据两种不同的三角形单元, 分别设计对应的12方向Freeman链码编码规则; 然后, 基于外轮廓前进相对方向的变化, 提出相对方向链码; 最后, 通过区分边界网格在外轮廓上的边数和内部网格数的不同组合, 得到边角组合链码。通过实验比较3种链码的表达能力和压缩率, 结果表明, 3 种链码方法均能克服顶点链的缺陷, 准确完备地实现三角形网格形状的边界表达。其中, 边角组合链码的综合性能最高, 平均码数为1, 压缩率可达0.75。