全站仪双边交会法测定树木三维坐标

林业调查中，林木遮挡不仅影响定位精度和工作效率，还会导致测量工作难以开展。全站仪自由设站法能有效解决林中通视条件差的制约。自由设站法有多种形式，由于林业调查精度要求相对较低，为了便于野外计算，双边交会法较为适宜。观测交会边长时，采用对边测量，能及时检测已测边长精度。直接解算仪器中心的三维坐标，无需对中和量测仪器高。实践表明，调查单元边长误差可小于5 cm，相对误差一般小于1/200，样地闭合差小于树木平均间距的1/2。图2表3参12

Tree's 3D coordinates positioned by two-side intersection with total station

In forest inventory,poor visibility caused by trees and shrubs often lowers the positioning accuracy and efficiency,sometimes even makes the survey difficult to carry out.Free-station method of total station can work well in poor visibility conditions.Due to relatively low accuracy required in forest inventory and in order to calculate conveniently in field,two-side intersection method is more suitable.When observing two sides,the method of missing line measurement can timely detect accuracy of measured length.It is unnecessary to aim straight at the mark and measure of instrument height if three-dimensional coordinates of the instrument center are directly calculated.Practices indicate that the side length error of inventory unit can be less than 5 cm,the relative error is less than 1/200,and closing error of sample plot is less than 1/2 of averagee distance between adjacent trees.