用活动觇牌视准线法观测大坝的水平位移时,一般是将经纬仪安置于视准线一端的固定工作基点上,后视另一端的固定工作基点,构成固定的基准线。这种观测方法,照准误差随着坝体的增长、大气的抖动而增大。此外,由于测站至后视点与至位移点距离不等,以致存在调焦误差。本文提出中点设站分段观测方法,对于较长的大坝,在不增加或不改变原有设 When observing the horizontal displacement of a dam by the activity plate sight line method, the theodolite is generally placed at a fixed working point at one end of the sightline and the fixed working point at the other end of the sightline forms a fixed reference line. This observation method, the accuracy of the error increases with the growth of the dam body, atmospheric jitter. In addition, there is a focus error due to the varying distance from the station to the backsight point to the point of displacement. This paper presents a midpoint set station observation method, for longer dams, without increasing or not changing the original set