H. González-Jorge

High performance grid for the metric calibration of thermographic cameras

The metric calibration of thermographic cameras would make possible the acquisition of geometric data if the principles of photogrammetry are followed. Both the distortion effects introduced in the images by the lens and the perspective effect can be corrected if the calibration parameters are known. This paper presents a calibration grid that allows the automatic metric calibration of thermographic cameras. This calibration grid is made of light and easy-to-find materials to guarantee its portability and handling. The calibration parameters obtained with the presented calibration grid are verified and compared with those obtained with a temperature-based calibration grid through the evaluation of the accuracy and repeatability in the modelling of a standard artefact previously certified.

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.

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.

Metrological comparison of terrestrial laser scanning systems Riegl LMS Z390i and Trimble GX

A low cost physical artifact with traceability to the national standard - meter is used for the metrological comparison of two terrestrial laser scanning systems: Riegl LMS Z390i and Trimble GX. The artifact is based on five spheres equidistantly situated and seven cubes of different dimensions. Accuracy and repeatability are evaluated using least squares fitting (LSF) and random sample consensus algorithms, for the study case of the spheres, and plane LSF and statistical analysis for the cubes. The horizontal resolution is evaluated using a modulated transfer function approach and the vertical one with the accuracy and repeatability data along Z axis. The Trimble system shows better results for all parameters, artifact parts, and algorithms under study.

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.

An Automatic Image-Based Modelling Method Applied to Forensic Infography

This paper presents a new method based on 3D reconstruction from images that demonstrates the utility and integration of close-range photogrammetry and computer vision as an efficient alternative to modelling complex objects and scenarios of forensic infography. The results obtained confirm the validity of the method compared to other existing alternatives as it guarantees the following: (i) flexibility, permitting work with any type of camera (calibrated and non-calibrated, smartphone or tablet) and image (visible, infrared, thermal, etc.); (ii) automation, allowing the reconstruction of three-dimensional scenarios in the absence of manual intervention, and (iii) high quality results, sometimes providing higher resolution than modern laser scanning systems. As a result, each ocular inspection of a crime scene with any camera performed by the scientific police can be transformed into a scaled 3d model.

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.

Procedure to induce a persistent current in superconducting cylinders or rings

A procedure to induce a persistent current in superconducting cylinders or rings was developed using a coil and a ferromagnetic core. Using the field cooling method, the current is induced from the combined effect of the coil magnetic field and the core magnetization. The proposed method was checked using four Bi-2223 samples. The main usefulness seems to be that a high persistent current can be induced using small both probe currents and coils.

Application of Kinect Gaming Sensor in Forensic Science

Kinect sensor appears as a low‐cost option for 3D modeling. This manuscript describes a methodology to test the applicability of Kinect to crime scenes. The methodology includes the comparison versus well‐established scanners (Faro and Trimble). The parameters used for the comparison are the quality in the fitting of primitives, a qualitative evaluation of facial data, the data quality for different ranges, and the accuracy in the measurement of different lengths. The results show that the Kinect noise level increases with range, from 5 mm at 1.5 m range to 15 mm at 3 m range. It is considered that for detail measurements the sensor must be placed close to the target. A general measurement of a sample crime scene was analyzed. Errors in length measurements are between 2% and 10% for 3 m range. The measurement range must be limited to c. 3 m.

Integration of UAV photogrammetry and SPH modelling of fluids to study runoff on real terrains.

Roads can experience runoff problems due to the intense rain discharge associated to severe storms. Two advanced tools are combined to analyse the interaction of complex water flows with real terrains. UAV (Unmanned Aerial Vehicle) photogrammetry is employed to obtain accurate topographic information on small areas, typically on the order of a few hectares. The Smoothed Particle Hydrodynamics (SPH) technique is applied by means of the DualSPHysics model to compute the trajectory of the water flow during extreme rain events. The use of engineering solutions to palliate flood events is also analysed. The study case simulates how the collected water can flow into a close road and how precautionary measures can be effective to drain water under extreme conditions. The amount of water arriving at the road is calculated under different protection scenarios and the efficiency of a ditch is observed to decrease when sedimentation reduces its depth.