I. Puente

NDT Documentation and Evaluation of the Roman Bridge of Lugo Using GPR and Mobile and Static LiDAR

AbstractThe Roman Bridge of Lugo (Spain) has undergone many restorations throughout the last millennium. It currently supports heavy and constant pressures resulting from traffic loading. Therefore, frequent inspections are required. Within this article, different nondestructive testing (NDT) technologies were combined for the inspection and as-built three-dimensional (3D) documentation of this masonry arch bridge. Both mobile and static light detection and ranging (LiDAR) devices, integrated with digital cameras, were considered to analyze the exterior of the bridge whereas the ground penetrating radar (GPR) equipment was used to characterize its internal stonework. A 3D textured bridge model is given, which is combined with inner details from GPR. Its analysis could certainly benefit masonry arch bridge inspection.

Single‐Image Rectification Technique in Forensic Science

Many researchers have been working in Spain to document the communal graves of those assassinated during the Spanish Civil War. This article shows the results obtained with two low‐cost photogrammetric techniques for the basic documentation of forensic studies. These low‐cost techniques are based on single‐image rectification and the correction of the original photo displacement due to the projection and perspective distortions introduced by the lens of the camera. The capability of image rectification is tested in an excavation in the village of Loma de Montija (Burgos, Spain). The results of both techniques are compared with the more accurate data obtained from a laser scanner system RIEGL LMS‐Z390i to evaluate the error in the lengths. The first technique uses a camera situated on a triangle‐shaped pole at a height of 5 m and the second positions the camera over the grave using a linearly actuated device. The first technique shows measurement errors less than 6%, whereas the second shows greater errors (between 8% and 14%) owing to the positioning of the carbon‐fiber cross on an uneven surface.

Reconstructing the Roman Site “Aquis Querquennis” (Bande, Spain) from GPR, T-LiDAR and IRT Data Fusion

This work presents the three-dimensional (3D) reconstruction of one of the most important archaeological sites in Galicia: “Aquis Querquennis” (Bande, Spain) using in-situ non-invasive ground-penetrating radar (GPR) and Terrestrial Light Detection and Ranging (T-LiDAR) techniques, complemented with infrared thermography. T-LiDAR is used for the recording of the 3D surface of this particular case and provides high resolution 3D digital models. GPR data processing is performed through the novel software tool “toGPRi”, developed by the authors, which allows the creation of a 3D model of the sub-surface and the subsequent XY images or time-slices at different depths. All these products are georeferenced, in such a way that the GPR orthoimages can be combined with the orthoimages from the T-LiDAR for a complete interpretation of the site. In this way, the GPR technique allows for the detection of the structures of the barracks that are buried, and their distribution is completed with the structure measured by the T-LiDAR on the surface. In addition, the detection of buried elements made possible the identification and labelling of the structures of the surface and their uses. These structures are additionally inspected with infrared thermography (IRT) to determine their conservation condition and distinguish between original and subsequent constructions.

Parameterization of Structural Faults in Large Historical Constructions for Further Structural Modelling Thanks to Laser Scanning Technology and Computer Vision Algorithms

Laser scanning technology has evolved significantly in the last decade, particularly, in those applications in terrestrial environments dealing with the documentation and inspection of civil engineering and architectural constructions. Even though there exist mature procedures to convert the so-called LiDAR point clouds in CAD models or even FEM models, the current trends in the technology are related to the automation of these operations. The development of robust automatic procedures for data segmentation and interpretation it is a key aspect so that the technology can definitely be accepted as a basic, accurate, and robust tool for reverse engineering of existing constructions. This paper presents the application of laser scanning technology to the structural evaluation of the Medieval Wall of Guimaraes (Portugal). This laser scanning survey was conducted with the aim of having an accurate and detailed geometrical model of the large masonry construction that includes the existing deformations and structural faults. The parameterization of structural damages was possible thanks to the highly detailed point cloud collected, and its processing using computer vision algorithms. The geometric models obtained could be used for further structural analysis of the entire wall.

GPR detection of underground pipes

Detection and location of buried pipes in the design of a building work is extremely important to ensure smooth and faultless working processes: this is to minimize the impacts to the services in the intervention area, avoiding for example, failures or leakages in the buried utilities, particularly massive in urban areas. This work presents the ground-penetrating radar as a solution to detect buried piping networks. An experimental zone was built including different types of piping and configurations. Four antenna frequencies were tested in order to provide an efficient field data acquisition and parameter setting that guarantees accurate results in detection.

Metrological evaluation of vessel-based mobile lidar for survey of coastal structures

Surveying of coastal structures is necessary to ensure that the structures are in good operating condition. Mobile lidar systems could be installed on vessels to monitor the coastal structures, even if there is no previous metrological information about their reliability. The aim of this work is to perform the metrological verification of the mentioned survey instruments. The verification methodology is based on the comparison of mobile lidar data from a breakwater with ground truth data provided by a Riegl LMS Z390i terrestrial lidar. Mobile lidar data are obtained from an Optech Lynx system installed on a vessel. The results show errors lower than 0.09 m based on distance measurements. Universal Transverse Mercator (UTM) coordinates show absolute errors lower than 0.12 m in the horizontal plane and 0.18 m in height. Precision analysis from the mobile lidar shows error values up to 0.055 m, while the terrestrial lidar gives 0.018 m for the same region of interest. The spatial resolution from the mobile lidar gives values of 321 points m‒2, in comparison with the 22,013 points m‒2 from the terrestrial lidar. Two point clouds from the same region of the breakwaters, obtained using the mobile and the terrestrial lidar, were triangulated and rasterized. The standard deviation of the vertical distances between the nodes of the raster data shows a value of 0.064 m. The results obtained show the potential of mobile lidar systems in combination with vessels for the monitoring of certain coastal structures, such as breakwaters, sea walls, bridges, wharves, and jetties.