(1) In areas with gentle changes in elevation anomalies, GPS method can be used for elevation control measurement. Data collection should use static relative positioning method, and the time should be greater than the time required for corresponding level of plane measurement.

　　(2) When using the fitting method to solve the elevation value, it is necessary to jointly measure the benchmark points at a higher level around and within the survey area. In plain areas, the number of benchmark points for joint measurement should not be less than 6; Hills or mountainous areas should not have less than 10 points. When there are many unknown points, the joint measurement points should be greater than 1/5 of the number of unknown points or the distance between the joint measurement points should not be greater than 5km. The benchmark points for joint survey should be evenly distributed in the network, and the polygon formed by the peripheral benchmark points should include the entire survey area. When dividing the survey area into several types of terrain, geometric leveling should be jointly measured at the changing terrain areas.

　　(3) According to the normal elevation difference between the GPS points obtained, the attached or closed elevation traverse is formed between the known points, and its closure difference shall comply with the regulations.

　　(4) Unknown points greater than 10% of the number of unknown points should be selected for verification, and the difference in height between them and known points should comply with regulations.

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