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建立高程控制网是水电工程测量的首要任务,在工程勘测、设计、施工、安装等各阶段,需要做大量的几何水准测量工作,这是一项量大而又细致的作业过程。由于西南地区的水电建设工地大多山高坡陡,地势险恶,因此几何水准测量作业难度比平坦地区要大得多。作业时因路线上地面起伏前、后视距离不可能绝对相等,且水平视线还受大气折光差的系统影响,每测100米高差系统误差约15毫米,即使采取措施加以改正,残存系统误差仍有25％～65％。
The establishment of elevation control network is the primary task of hydropower engineering measurement. In the stages of engineering survey, design, construction and installation, a great deal of geometric leveling work needs to be done. This is a large and detailed operation process. As most of the hydropower construction sites in southwestern China are steep and steep on the terrain, the geodetic leveling operation is much more difficult than in the flat areas. When the operation due to undulating ground before and after the line of sight can not be absolutely equal distance, and the horizontal line of sight is also affected by atmospheric refractive index difference of the system, each test error of 100 meters height difference of about 15 mm, even if measures are taken to correct the residual system error Still 25% ~ 65%.