Abstract: The connecting line is quite different from the main line in detour mode, single and double lines, track structure, design speed and design height, and the maintenance and inspection during the operation period require the whole line CPⅢ to be measured and laid out. The connecting line has no available pole and column structures for CPⅢ layout due to single line detour, and the CPⅢ survey is difficult to see due to terrain elevation difference. Through on-site investigation and data comparison and analysis of many railways such as Nanjing-Qidong Railway and Nanjing-Hangzhou Railway, the research conclusions are put forward:First, the types of CPⅢ layout using existing pole and column structures are enriched; The second is to develop non-mandatory centering CPⅢ logo; Thirdly, the method of co-point network distribution in the connection section is studied. Among them, 4 national patents have been obtained for non-mandatory centering CPⅢ marks. The co-point network distribution method for connecting sections reduces the burying workload and joint measurement workload, thus greatly improving the work efficiency. A novel concept such as "CPⅢ co-point is adopted for encrypted CPⅡ, and CPⅡ co-point is adopted for encrypted level" is put forward, which can provide basic data for GNSS elevation measurement and elevation anomaly research.

Key words: connecting line, track control network CPⅢ, free observation station, triangular elevation, common point