PHOTOGRAMMETRIC 3D MEASUREMENTS IN FORESTS WITH ACTION CAMERAS

Abstract. This paper presents a study of the application of action cameras, such as the GoPro, for the extraction of 3D models in a forest environment. These cameras are very small and can be used by any operator, even in other forestry works, to collect imagery for photogrammetric post processing. The method implemented uses the Structure from Motion approach in order to obtain the 3D model. The model becomes georeferenced by means of the camera positions which are recorded by the camera navigation GPS receiver. The aim of the study is to assess the geometric accuracy of such methodology, especially in relative terms, in the evaluation of object dimensions. Several tests were carried out both in open sky and under trees, with worse conditions for GPS positioning. The results pointed to scale accuracy of around 3%, which may be acceptable for many applications. Accuracy can be improved by using a scale bar of known length placed in the scene. The method is intended to be used in tree measurements for forest inventory or other outdoor measuring.