ABSTRACT
During the last years, thanks to the availability of commercial and low-cost UAVs (Unmanned Aerial Vehicles), surveying by means of 3d reconstruction generated by computer vision algorithms is having a rapid growth. These tools allow for a quick and effective methodology to acquire image data and reconstruct a detailed 3d model that can be used for structural analysis and maintenance operations. In this context, this paper presents an application example of a commercial mini-UAV equipped with a low-cost camera in an aerial photogrammetric survey of a bamboo-steel spatial truss roof system, with the purpose of obtaining the as-built drawings. This roof system is located at the entrance of the College of Civil Engineering of the Nanjing Tech University and is made by a spatial truss system supporting a glass roof in which the GluBam beams are used for the upper chord and the diagonal elements, while steel tubes are used for the lower chord. The developed methodology for acquiring data through UAV is introduced, specifying the flight acquisition plan to obtain the images data, and the data processing using structure-from-motion algorithms to provide an accurate 3d-model. The accuracy of the measurements is evaluated by comparing results with project drawings. Moreover, the use of the obtained 3d model and photo dataset in practical application is discussed. The results highlight the economical and fast applicability of this technology to the survey of spatial truss structures to derive a 3d model, which can also be used to acquire useful information on the structural health conditions.Surveying techniques for the acquisition of spatial information are rapidly growing during the last years thanks to the availability of new technologies and instruments (both software and hardware). The digitalization of the construction industry is revolutionizing the design process and the entire life cycle, in particular the maintenance process. Modern surveying techniques are fundamental to acquire spatial information and convert it into digital information, in case blueprints are not available, and also to analyse and monitor the structure and to schedule maintenance works.
