Key Technology on Establishment of an Independent CoordinateSystem for Water Diversion Project in Central Yunnan

Objective A water diversion project in Central Yunnan exhibited several typical characteristics of theoverall survey region,such as the extraordinarily long span,the high average altitude,and large ele-vation changes.Therefore,difficult to build independent coordinate system for this project.Based onthe theory of projection distortion,we propose a key technology solutions composed of two parts.First,using the 1°projection zone to replace the regular 3°projection zone,Gauss projection distor-tion was effectively controlled.Second,a method for selecting a compensation projection plane wasdeducted to satisfy the needs of this water diversion project.An optimized solution for this project wasfound using the proposed independent coordinate system and efficiently controlled,the maximum com-prehensive deformation for this water diversion project in Central Yunnan.