3D Modelling of Inaccessible Areas using UAV-based Aerial Photography and Structure from Motion

Abstract

In hardly accessible areas, aerial photogrammetry and laser scanning with manned flight are normally used for topographic measurement. However, those methods are expensive and therefore frequent measurement is practically difficult. To solve such problem, the authors have experimented an aerial photography based SfM (Structure from Motion) technique on a ‘peninsular-rock’ surrounded on three sides by the sea at a Pacific coast in Chiba Prefecture. The research was carried out using UAS (Unmanned Aerial System) combined with a commercial small UAV (Unmanned Aerial Vehicle) carrying a compact camera. The 3D model has been constructed by digital photogrammetry using a commercial SfM software which can generate sparse and dense point-clouds, from which polygonal models and orthophotographs can be calculated. Using the ‘flight-log’ and/or GCPs (Ground Control Points), the software can generate digital surface model. As a result, high-resolution aerial orthophotographs and a 3D model were obtained. The results have shown that it was possible to survey the sea cliff and the wave cut-bench, which are unobservable from land side. This system has several merits: firstly lower cost than the existing measuring methods such as manned-flight survey and aerial laser scanning. Secondly, compared to these other methods, the one the authors have presented also enables frequent measurements. Thirdly lightweight and compact system realizes higher applicability to various fields.