The present contribution investigates the effective layout of Ground Control Point (GCPs) that enables the construction of high-precision three-dimensional topographic model of steep cliff slopes using UAV-SfM survey. The surveys were conducted for the coastal cliffs (Benten island in Tomari Village and Obira, Shimamaki Village) in Hokkaido. The terrain model constructed from UAV-SfM (UAV reference model) was first compared with the terrain model derived from TLS survey. Both surveys were performed under the condition that GCPs were evenly arranged in the vertical and horizontal directions. The difference between the terrain models of UAV-SfM and the TLS was calculated to be less than 10 cm. Secondly, we compared the following three UAV models generated under different GCP arrangement with the UAV reference model; 1) “Model with GCP placed only in the lower part of the slope” (the lower model), 2) “Model with GCP placed in the lower and central part of the slope” (the lower and 3) “Model with GCP placed in the lower part and upper of the slope” (the lower and The results of this second part of the research have revealed that the lower model caused larger difference with the UAV reference model in both study sites, while the lower and upper model and lower and central model showed only small differences with the reference model. Moreover, the number of GCPs in lower and upper model was smaller than the other model. In conclusion, the present research shows that the most effective arrangement of GCPs on the studied cliffs were positioning on the lower and the upper slopes.
