# Aerial Robotic Solution for Detailed Inspection of Viaducts
## 2 System Description  
The proposed viaduct inspection system offers a comprehensive solution to check and to evaluate the condition of these infrastructures through its integrated tools. A workflow has been created that meets the needs to speed up, reduce the cost, and increase the safety of these inspections. All the tasks are carried out with aerial robotic platforms whose characteristics are chosen according to the task to be performed. These tasks can be general and/or detailed photographs or make physical contact with the structure to take measurements with sensors as required. The workflow is shown in Figure 2 and is as follows. Given a viaduct of interest on which an inspection should be performed, the proposed workflow begins with the creation of a mission. During this phase, it is required to acquire a 3D map of the structure in which the inspector can select the areas and points of interest. This 3D map is not only useful for the creation and subsequent visualization of the mission, but it is also required for the global localization of the aircraft. It is obtained with the help of a robotic total station that establishes an arbitrary coordinate system and performs scans to obtain the 3D points around it. It is important to capture these data from different points of view to obtain a complete point cloud of the viaduct. To facilitate the subsequent use of this map, the reference system should be aligned with the _ENU_ axes (**x** = East, **y** = North, **z** = Top). If possible, it is desirable to obtain an approximate GNSS coordinate of the origin of the point cloud to locate it globally. Otherwise, this can be done manually. The use of the total station is then limited to one time only. Once the map has been created, it can be reused in all subsequent inspections, provided that the viaduct has not suffered significant changes. With the points and areas of interest selected on the 3D map created, this information is sent to the aerial platform, which translates it to its local coordinate system and creates the route of waypoints and actions necessary to carry out the inspection autonomously capturing overlapping pictures. This mission is then a first general visual inspection of the structure to locate any possible defect. This check is performed by taking general pictures of the structure with high resolution in an automated way using the visual inspection platform described in Section 2.1. After the first general pictures are taken, they are analyzed to check the condition of the viaduct, paying special attention to those areas where a defect is suspected. This analysis can be performed manually by an inspector or automatically by applying an automatic image defect detection algorithm, like [28; 29]. After the analysis, a decision should be made to determine if more detailed information on the defects found or suspect areas are required. If so, more detailed visual or contact information may be obtained using the visual or contact inspection platforms, respectively. In case more visual information is required, the mission previously created by the inspector can be reused but using another camera configuration that better collects the required information. For example, a different lens can be used for the camera with a longer focal length to obtain better details of the specific area. However, if the previous mission does not meet the requirements of the new visual inspection, the inspector can create a new one with the 3D map and select the previously found defects. When the missions are finished and the visual information obtained is sufficient, our proposed solution also considers the use of a specific platform for contact inspections. This platform is described in Section 2.2 and has a robotic arm with an end effector on which a sensor can be installed. In case of finding defects in the visual inspection that require a deep analysis with specific sensors that require physical contact with the structure, this platform is sent to those defects and captures data.