Abstract: The survey point of the section shall be located on the section line , but the survey point “devi-ates”from the section line due to external conditions and some other factors. How to make full use of theso-called “deviation”data to draw the section line and its engineering application is very important. Inview of the above problems, this paper proposes a section modulation method based on the spatial planefitting method. Compared with the trigonometric network method and contour method in CASS, the resultsof the three methods are consistent, and the elevation difference meets the requirements of the specifica-tion. However, this method does not need to measure points on the section line, and can resample pointson the section line for fitting, especially suitable for river section measurement. This method is worth pop-ularizing and applying.

Key words: cross section , spatial plane fitting, resample, modulation