DIRECT GEOREFERENCING APPROACHES FOR CLOSE-RANGE AND UAV PHOTOGRAMMETRY IN THE BUILT HERITAGE DOMAIN

Abstract. Direct georeferencing uses onboard sensors to measure the position and orientation of the camera during image acquisition for photogrammetric applications. This approach aims to eliminate the use of traditional Ground Control Points (GCPs) in the photogrammetric process in order to reduce the costs and the time of the survey operations. The direct georeferencing technique involves integrating measurements from inertial measurement units (IMUs) and Global Navigation Satellite Systems (GNSS) data in order to evaluate the position and attitude of the camera with high accuracy (a few centimeters). In the Built Heritage survey domain, this approach is mainly followed by the employment of UAVs (Uncrewed aerial systems) platforms that are nowadays equipped with highly accurate systems able to evaluate the external parameters for the photogrammetric process. For terrestrial applications, few already achieved tests were performed; moreover, the sensors today available for extracting information from close-range acquisition systems are limited and sometimes under development. To evaluate the possibility offered by these new direct georeferencing tools, a test on the 3D ImageVector (REDcatch GmbH) has been performed. The results and the strategies followed will be presented and analyzed in order to understand better the accuracy and the potentiality of this new promising approach.