Structure from motion technique of proximal sensing airborne data for 3D reconstruction of extraction sites

Nowadays digital photogrammetry utilized together with Structure from Motion (SfM) algorithms represents a low-cost and rapid technique for the tridimensional detection and mapping of large areas of particular geologic-geomorphologic and environmental interest. In this case study, we use images captured from sensors mounted on a small and inexpensive aircraft for the 3D morphological reconstruction of extraction sites. The aircraft, called RadGyro, is able to deal with morphologically complex zones, as the test area, located in the marble district of the Apuan Alps, the biggest and most exploited European extractive basin. The RadGyro is equipped with two digital cameras (full frame sensor and 35 mm fixed lens), five GPS antennas, and an Inertial Navigation System (INS) that allow association of each frame to the camera position and its angular orientation. Ground Control Points (GCPs) acquired through traditional topographic surveys allow improvement of the image exterior orientation as well as the SfM techniques permit detecting millions of tie points for an accurate relative alignment of photos. Finally, the photogrammetric processing is completed by creating 3D point clouds, Digital Surface Models (DSM), Digital Terrain Models (DTM), and orthophotos. The results, here presented, emphasize the potentials of the RadGyro and demonstrate how SfM algorithms can be very useful in the photogrammetric processing and in the geological, geomorphological and geo-structural interpretation and analysis.