分组法求点方向图，邻域方向模板法求点方向图（也称B.M.Mehtr法），切缝法求点方向图，改进方法求点方向图，由改进方法得到的点方向图求连续分布方向图-Grouping method the dot pattern, the direction of the template method the neighborhood point pattern slit method the dot pattern, the direction the point of improved methods