Abstract: The upright surface information of targets such as building walls, cliffs or dangerous rocks plays a very important role in the fine modeling of objects and investigation, analysis, evaluation and prevention of geological disasters. The images obtained by traditional oblique photogrammetry lack a detailed description of the vertical surface information of the target, and in areas with large changes in height difference, modeling may fail due to different image overlap rates. The ground-like flight strategy solves the above problems to a certain extent, but for areas with sudden changes in altitude, it is often unable to meet the requirements of refined modeling. This paper proposes a new ground-like flight method based on contour lines to construct drone routes. This method generates contour lines based on the DSM of the target area, and completes the design of the drone route through contour simplification and offset. The model results constructed by this method are compared with the modeling results of the traditional ground-simulating flight method. The experimental results show that the method proposed in this paper is more realistic for portraying dangerous rocks on cliffs. Moreover, compared with the traditional ground-like flight method, the flight route designed in this paper avoids frequent altitude changes, which is beneficial to extend the time for the UAV performing flight tasks. Therefore, the new ground-like flight method based on contour lines to construct drone routes proposed in this paper is a very effective and practical flight route design method.

Key words: photogrammetry, refined modeling, DSM, contour lines, ground-like flight