在公路测量中，如遇直线上有小山头等，端点A、B互不通机（图1），常用逐渐趋近法来标定直线。图1中，在A、B两点各竖立一根花杯，由甲测量员选一点C，立一根花仔，C．点尽可能位于AB直线附近，并能看见A、B两点。然后甲测量员指挥动测量员在C；B线广定一点D；，而D，要能看见A In the road survey, in case there is a hill on the straight line, the endpoints A and B are not connected to each other (Figure 1), the commonly used gradual approach to calibrate the line. In Figure 1, two flower cups are erected at points A and B, one point C is selected by A surveyor and the other is a flower. As close as possible to the AB straight line, and can see A, B two. Then A surveyors command the surveyors in the C; B line to set a little D ;, and D, to see A