B. Riveiro

Automatic Morphologic Analysis of Quasi-Periodic Masonry Walls from LiDAR

This article presents a novel segmentation algorithm that allows the automatic segmentation of masonry blocks from a 3D point cloud acquired with LiDAR technology, for both stationary and mobile devices. The point cloud segmentation algorithm is based on a 2.5D approach that creates images based on the intensity attribute of LiDAR systems. Image processing algorithms based on an improvement of the marked-controlled watershed was successfully used to produce the automatic segmentation of the point cloud in the 3D space isolating each individual stone block. Finally, morphologic analysis in two case studies has been carried out. The morphologic analysis provides information about the assemblage of masonry pieces, which is valuable for the structural evaluation of masonry buildings.

Ancient Stone Bridge Surveying by Ground-Penetrating Radar and Numerical Modeling Methods

Bridges are considered necessary engineering structures because they connect separated lands to improve economic and social development. In Spain, many of the bridges in service within the network of transport are masonry arch bridges built in ancient times. In addition to their age, the stability of these remaining bridges is questionable because of the changing loading conditions; therefore, they require periodic assessment of the condition state. Moreover, some of these bridges are considered a part of the cultural heritage of a region, so nondestructive evaluation is required to preserve their historical character. In this work, a medieval stone bridge in the Galician territory of Spain was evaluated using ground-penetrating radar, supported by a detailed geometric survey performed through a terrestrial laser scanner. The results revealed unknown geometrical data and hidden characteristics, including the thickness of ring stones in the interior of the vault, as well as the presence of ancient arches and restorations. To assist in the interpretation, finite-difference time-domain modeling was used, where realistic models were built from the accurate geometry provided. The synthetic data obtained were compared with the field data, which allowed for the identification of unknown structural details.

Automatic Segmentation and Shape-Based Classification of Retro-Reflective Traffic Signs from Mobile LiDAR Data

Recently, many studies have demonstrated the valid contribution of mobile laser scanning to road safety improvements, thus intense efforts have been made to implement automatic data processing using laser scanning data, with special emphasis on road object recognition. This study is focused on the detection and classification of retro-reflective vertical traffic signs according to their function (danger, give way, prohibition/obligation, and indication) from mobile laser scanning data by considering geometric and radiometric information, but without relying on trajectory data. The global strategy for segmentation involves the application of an optimized intensity threshold in order to segment the points that correspond to traffic sign panels. Next, contour recognition is performed for each sign using a linear regression model based on a raster image, which is generated for each cluster of points. The shape evaluation is motivated by the correspondence between contour shape and function of the traffic. The completeness of results for detection (92.11%) and classification (83.91%) demonstrates that this implementation is promising for the automatic detection and inventory analysis of traffic signs in road mapping applications. The efficiency rates are acceptable in urban areas, but our tests indicate that the detection and classification rates are more robust in road environments.

Verification artifact for photogrammetric measurement systems

A low-cost mechanical artifact is developed for the metrological verification of photogrammetric measurement systems. It is mainly composed of five delrin spheres and seven cubes manufactured in different sizes. A set of circular targets are fixed on these elements to perform the photogrammetric restitution. The artifact is used in order to compare three photogrammetric systems defined by three different cameras (Canon 5D with 14-mm lens, Nikon D200 with 20-mm lens, and Jai BB500GE with 8-mm lens). Photomodeler Pro and Matlab software are used for the data processing. The precision of the systems is evaluated using the standard deviation of the geometric coordinates calculated from the restitution of the circular targets. The accuracy is calculated using two different procedures: one of them uses the distance between the center of the spheres and the other uses the distance between the faces of the cubes. The comparison between the photogrammetric systems and their associated calibration files reveals that the Jai camera produces the best results in terms of precision and accuracy, while the Canon camera produces the poorest ones. The bad results from the Canon system are primarily related to the low quality of the calibration procedure.

Automatic Inventory of Road Cross-Sections from Mobile Laser Scanning System

This article aims to automatically obtain the geometrical inventory of road cross-sections i.e., number of lanes, width of the roadway, width of the shoulders, width of the lanes, superelevation using a mobile laser scanning MLS system. Because of the large amount of data captured by the MLS, we have developed a methodology that is based on a process of segmentation, classification, and extraction, which allows us to determine the geometrical cross-section parameters. The process was validated with real data from motorways, and satisfactory results were obtained in the analyzed scenarios.

Application of close range photogrammetry to deck measurement in recreational ships.

In this article, we present results that demonstrate the utility of close range photogrammetry in the measurement of decks in recreational craft as an alternate measurement system to the one based on direct acquisition of coordinates. The areas of deck covered with teakwood for aesthetic or security reasons were measured. Both methods were compared in terms of precision of measurements, time consumption, equipment cost, and ease of manipulation and equipment transportation. Based on the results, we conclude that photogrammetry has advantages in almost every aspect with respect to the direct method. Consequently, photogrammetry is suggested as a suitable method for coordinate measurement of decks in recreational ships. However, in some special circumstances, where ships have wide corridors with few obstacles the direct method can be more appropriate than the photogrammetric method.

Performance testing of LiDAR exploitation software

Mobile LiDAR systems are being used widely in recent years for many applications in the field of geoscience. One of most important limitations of this technology is the large computational requirements involved in data processing. Several software solutions for data processing are available in the market, but users are often unknown about the methodologies to verify their performance accurately. In this work a methodology for LiDAR software performance testing is presented and six different suites are studied: QT Modeler, AutoCAD Civil 3D, Mars 7, Fledermaus, Carlson and TopoDOT (all of them in x64). Results depict as QTModeler, TopoDOT and AutoCAD Civil 3D allow the loading of large datasets, while Fledermaus, Mars7 and Carlson do not achieve these powerful performance. AutoCAD Civil 3D needs large loading time in comparison with the most powerful softwares such as QTModeler and TopoDOT. Carlson suite depicts the poorest results among all the softwares under study, where point clouds larger than 5 million points cannot be loaded and loading time is very large in comparison with the other suites even for the smaller datasets. AutoCAD Civil 3D, Carlson and TopoDOT show more threads than other softwares like QTModeler, Mars7 and Fledermaus.

Modelling and strength evaluation of masonry bridges using terrestrial photogrammetry and finite elements

Several numerical models are presented in this article, for the study of the ultimate behaviour of a real stone arch bridge. For the exact representation of the geometry an integral and comprehensive survey involving Terrestrial Photogrammetry and Ground Penetrating Radar is in order to provide a realistic 3D geometric model for the subsequent mechanical analysis of the bridge. The accuracy of the photogrammetric method permitted detecting cracks in different areas and the GPR completed the geometric model with information of hidden parts such as backfill, arch ring thickness, etc. Finite element analysis models, incorporating damage, elastoplasticity and contact, are then developed. Comparison between these models is considered in a single arch of the structure. The classical four hinges mechanism appears in the arch. A model of the whole structure, where the arch and the fill are taken into account, is finally developed. Results show how damage is developed in the body of the arch, for loadings that include forces, or vertical and transverse displacements in the supports.

A methodology for the inventory of historical infrastructures: documentation, current state, and influencing factors

This study is focused on the development of a methodology for the study of historical bridges. The discussion is divided into several parts: 1) a description of a simple methodology to quickly acquire data during the inspection of historical bridges; 2) a report on the current state of 88 historical bridges located in the Galician Country; 3) a data storage system for automated diagnosis of bridges, based on criteria determined by an expert staff; and 4) an exploration of trends and other factors can be related to the conservation of these bridges. Some of the more important bridge features that were obtained in this project are the geometry, construction, pathologies and structural damage in the bridge. The data were managed using digital databases and GIS. This approach enabled focused, deep inspection for bridges with urgent problems. Finally, results are presented with the conclusion that public policies to maintain bridges have not been sufficient. In fact, conservation actions have normally been carried out only after problems are detected, so public authorities apply corrective measures instead of preventive ones.

Experimental forensic scenes for the characterization of ground-penetrating radar wave response

Over the last few decades, the use of non-intrusive geophysical techniques, which allows for coverage of an entire crime scene in a reasonable amount of time, in forensic investigation has increased. In this study, we analyze the effectiveness of ground-penetrating radar (GPR) in forensics. Experimental scenes were simulated and some of the most commonly buried items in actual crime scenes were introduced, such as bone remains, guns and drug caches. Later, a GPR survey was conducted on the experimental grids with a 500 MHz antenna. The final purpose was to characterize the radar wave response expected for each set of remains to assist with its identification in later actual investigations. The results collected provided promising information that can be used when surveying real cases. Nevertheless, there were some interpretational difficulties regarding the sizes of the items and the electromagnetic properties of the materials. For these cases, finite-difference time-domain modeling was employed to achieve an advanced interpretation of the field data. The simulated models used were built from accurate geometric data provided by photogrammetric methods, which replicate the experimental scenes in fine detail. Furthermore, this approach allowed for the simulation of more realistic models, and the synthetic data obtained provided valuable information for assisting in the interpretation of field data. As a result of this work, it was concluded that GPR can be an effective tool when searching for a variety of materials during a crime scene investigation.