Dynamic 3D network design for UAV-based photogrammetry in mountainous terrain

Topographic mapping in mountainous areas encounters many challenges due to the potential impasse and lack of access to all locations. Unmanned Aerial Vehicles (UAVs) are an effective alternative to traditional field mapping in different environmental conditions. However, problems, such as large-scale differences, gaps, and errors due to extreme elevation differences in these areas, hinder the use of UAV-based photogrammetry, thus reducing the quality and accuracy of the photogrammetric products and the final extracted map in mountainous areas. By designing an optimal flight network before UAV acquisition, the effect of these problems can be reduced. This paper proposes a method for planning the dynamic three-dimensional imaging network UAV in mountainous terrain based on digital elevation model (DEM) to ensure the uniformity of the scale in the photogrammetric blocks, and avoid collision with obstacles, also gaps or data redundancy. The proposed method was implemented in a semi-mountainous area and was compared to two approaches of 3D network with static overlap and normal 2D flight plan. The results showed that the large-scale changes among the images were reduced and the ground sample distance (GSD) was maintained as constant as possible. Also, planning UAV flight program based on the proposed algorithm increases the accuracy of the photogrammetric products.