Objects  Micro landform is an important basis for safe operation of transmission lines engineer‍ing, the risk division of lines icing and the calculation of energy consumption during the construction period of transmission lines. As the national grid extends and voltage levels increases, there are a lot of transmission lines passing through the micro landform area and damaged seriously. The traditional macro geomorphologic map can not show the micro landform characteristics accurately. It is subjective and costly for identifying micro landform by experts on the spot base on aerial photography and satellite images. Furthermore, it is difficult to meet actual engineering requirements. The automatic extraction micro landform of transmission lines is not only a requirement for digital transmission lines landform analysis precisely, but also a prerequisite and guarantee for the construction of power grid projects under complex landform conditions.

  Methods  According to the classification system of micro landform in the specifications, the micro landform types of transmission lines were investigated and five micro landform types including yakou, mountain, uplift, canyon and vapor were proposed. The micro landform type with yakou, mountain, uplift, canyon focuses on regional terrain complexity and relief, as while vapour landform focuses on the causes of the disaster. A decision-making scheme was proposed by terrain position index, slope, relative el‍evation and water distance, and a method of transmission line micro landform extraction based on grid dig‍ital elevation model(DEM) was constructed. About the vapor landform, the water distribution data were applied to the experimental area, the water area units were divided, and water body distance was calculated by grid statistics.

  Results  9 transmission lines DEM data of a power grid company during 2012—2018 were used for extraction experiment. The micro landform type of yakou, mountain, uplift, canyon and vapor was extracted effectively, the position and tendency of the micro landform could be discriminated by the extraction results, and the statistical parameters of each transmission lines micro landform in the experimental area were obtained. A comparative analysis of disaster data form the influence of micro landform was add‍ed. It was found that the proportion of typical micro landform area where the disaster occurred was over 90%, much higher than the proportion of micro landform in the non-disaster area.

  Conclusions  The topographic position index, slope, relative elevation and water body distance were adopted to describe the five typical micro landform characteristics of the transmission line with digital terrain analysis technology and the existing transmission line micro landform classification system. Mined the micro landform information, a micro landform extraction method of grid DEM for transmission line was established. Compared with the traditional manual sketching method, it is simple and efficient, and the boundary contour of the extraction results was obvious, which could provide basic support for transmission line construction.