PSI - Issue 62

Antonio Di Pietro et al. / Procedia Structural Integrity 62 (2024) 755–762 Antonio Di Pietro et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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transmission becomes problematic. This is where Post-Processed Kinematics (PPK) is to be preferred since the data correction is provided off-line through a specific software. 4. Measurement of characteristic quantities for the Scale Bar process and initiation of GCP acquisition Th Scale Bar function is a backup process aiming at addressing potential limitations related to RTK data link availability, which might experience issues such as signal weakness, signal loss, or intermittent connectivity. To ensure the accuracy of the collected data for post-processing, the following steps can be employed: • Field Data Collection: Field measurements are acquired using surveying equipment or aerial photogrammetry techniques. These measurements include critical details about various bridge components, such as deck, abutments, piers, and other structural elements. • Scale Bar Implementation: A scale bar, in the form of a master component of the reference object bridge of known length is introduced into the scene during data capture as a known scale reference, and its length is accurately recorded. • Scale Bar Data Back-Up: Prior to the flight operation phase, during the placement of the ground target, as a precaution against potential RTK signal issues, the Scale Bar function is put into action. The known length of the scale bar is specified within the photogrammetry or surveying software to introduce a reliable scale to the 3D model. • Data Fusion and Post-Processing: The field measurements, including the use of the Scale Bar function, are combined with RTK data. This fusion of data from different sources enriches the dataset, enhancing the accuracy and completeness of the information available for post-processing. • Quality Assurance and Validation: Post-processing involves quality checks and validation procedures to ensure that measurements, including the scale, are correctly aligned and accurately represent the bridge components. • Final Data Set for Analysis: The integrated dataset, including measurements from RTK, the Scale Bar function, and other field data, forms the basis for detailed post-processing and analysis. This comprehensive approach enables precise 3D reconstructions and modeling of the bridge. By implementing the Scale Bar function alongside RTK data acquisition and field measurements, the amount of data collected for post-processing is significantly enhanced, resulting in a more comprehensive and accurate representation of the bridge main components and its overall arrangement. 5. Use of the UAS in manual flight and automatic functions There are significant differences between automatic and manual flights used in aerial photogrammetric surveys. Using automatic flight relieves the remote pilot from the need to focus solely on piloting. As a result, this mode is preferred whenever feasible. A crucial distinction is based on the ability to perform a preliminary inspection, as new structures not on the latest available map, such as Google's, might arise. With manual flights, the drone trajectory is determined in advance, following a pre-established route. This method requires meticulous attention to both the path and data collection and it is therefore recommended that at least two operators handle this kind of flight. In contrast, with automatic flights, direct control of the drone is minimal, restricted only to critical situations. The focus is mainly on accurately capturing images and ensuring the drone remains continuously visible to the remote pilot. The flight mode influences operational protocols. For automatic flights, the flight and shooting directives are set upstream and uploaded to the drone software, then transmitted to the designated application. For instance, when mapping a flat area, software connected to a remote control is used, often referring to maps such as Google. Assuming the intention to conduct nadiral-oriented shots, the GSD is determined based on flight altitude, and overlapping trajectories are designed, typically with a 60-70% coverage. Subsequently, boundaries, speed, and shooting interval are determined, ensuring consistent overlap between photos. Some software provides advanced features, such as dynamic trajectory modification. The choice between automatic and manual flight is often conditioned by the object of the survey. For structures such as bridges, manual flights might be more appropriate due to the object features and potential difficulties in receiving the GNSS signal in certain areas.