一、后方交会法观测计算的缺点经纬仪后方交会法具有外业作业简单的优点。但在观测计算上的缺点是:(一)一般三角网或锁都是接近等边三角形的,因此边长 AB 与 AC 常接近或相等。补测交会点时,为得到较好的图形,总希望使∠α和∠β接近60°,如图1。在这种条件下,常用的解算∠B 和∠C 所用的参数 tgφ=ACsinα/ABsinβ的值接近于1。因此,φ接近于45°,φ-45°经常很小,有时小于5°～10°。因此 tg(φ-45°)这个因子的秒差变 First, the rear intersection method to observe the shortcomings of calculation Theodolite rear intersection method has the advantage of simple field operations. But the shortcomings in the observation and calculation are: (a) the general triangle or lock are close to the equilateral triangle, so the side length AB and AC often close or equal. When measuring the intersection, in order to obtain a better figure, it is always desirable to make ∠α and ∠β close to 60 °, as shown in Figure 1. Under these conditions, the value of the parameter tgφ = ACsinα / ABsinβ used by the commonly used solvers ∠B and ∠C is close to unity. Therefore, φ is close to 45 ° and φ-45 ° is often very small, sometimes less than 5 ° to 10 °. So tg (φ-45 °) this factor changes second