1,721,746 research outputs found
Video Motion Magnification to Improve the Accuracy of Vision-Based Vibration Measurements
Full text linkVideo motion magnification (MM) allows to turn a tiny movement recorded on video into an easily visible displacement. In this work, such techniques are employed to decrease the uncertainty of vision-based motion measurements. Previous works have already combined MM with vision-based measurement techniques, such as digital image correlation. This present study analyzes its applicability on simpler measurement techniques: pattern matching and edge detection, analyzing the accuracy improvements when measuring on a motion-magnified video. In addition, the suitability for these purposes of recent MM algorithms is tested, and the circumstances under which the magnification is beneficial are studied. As a result of the experiments, it is concluded that MM can increase the motion measurement accuracy, especially for small displacements, which could be considered an initial step for future quantifications of its applicability range
2D DIC from single moving camera by homographies compensation
No full textThe use of unmanned aerial vehicles in combination with vision-based measurement techniques has increasing interest in structural health monitoring. When displacement fields must be measured, Digital Image Correlation is one of the most popular techniques for image analysis. However, when images are taken from a single camera mounted on a drone, DIC gives incorrect results, since the camera movement creates apparent displacements and deformations. In the paper a technique for the compensation of these perspective distortions is proposed for planar surface case. The technique uses homographies estimated on a limited region of the measurement target assumed undeformed. Tests on numerically generated images have been performed to validate the proposed algorithm and to study the effect of the non-complete compliance with theoretical assumptions. Model for compensation error prediction is also proposed. Finally, some experimental tests considering real targets have been performed, obtaining good performances for the crack aperture case study
ALWIN BERGER, CURATOR OF THE HANBURY BOTANICAL GARDENS AT LA MORTOLA
No full textAlwin Berger (1871-1931) spent eighteen years at La Mortola as Curator (1897-1915). We outlined his contribution to development and displays of scientific collections of the garden analysing some original historical documents. A selection of original botanical photographs made by A. Berger was included here
Virtual simulation benchmark for the evaluation of simultaneous localization and mapping and 3D reconstruction algorithm uncertainty
Full text linkSimultaneous localization and mapping (SLAM) algorithms allow us to obtain a unique 3D shape and 3D sensor trajectory by combining partial scans obtained by moving a 3D scanner. The performances of these algorithms are significantly affected by experimental conditions, characteristics of the target and values of the parameters of the reconstruction algorithm. Therefore, the uncertainty and reliability of SLAM techniques need to be assessed before their application, e.g. for robot navigation, autonomous vehicles or industrial fields. To evaluate the uncertainty of these algorithms, specific datasets containing 3D scans, with the possibility to control different conditions, e.g. sensor trajectory, depth or color noise, sensor velocity and framerate, are necessary. In this article, we present a procedure to obtain virtual datasets with complete control of the environment, 3D sensor and trajectory conditions, starting from any real 3D dataset acquisition, characterized by a sufficiently low uncertainty. These datasets can be generated to test the effect of SLAM algorithm parameters to determine the best parameters to be used to exploit the algorithm characteristics to obtain the best result in each operating context. The advantage of this procedure is the possibility to perfectly control each condition and to evaluate its effect on the final result. This procedure was applied to two reconstruction algorithms as examples; namely, the Open3D reconstruction tool and ElasticFusion. The results demonstrate that the setting of algorithm parameters, e.g. the tolerance on depth correspondence between frames or the number of fragments, or the change in number of frames acquired, can have a strong influence on the resulting 3D reconstruction and trajectory. Moreover, the effect of not closing the loop trajectory on reconstruction performance is quantified for different application scenarios
A “mechanical” vision of image-based identification methods in structural dynamics
No full textImage-based measurements are nowadays well-established techniques, and their further development seems endless considering the fast evolution of cameras, computer hardware and software. New algorithms for structural dynamics are continuously developed and, frequently, made available in the computer community. On the other hand, experimental set-up is still an issue. This tutorial aims to focus the attention to this aspect, and will cover:The basic of the experiment design;The selection of the hardware set-up (object preparation, lighting, cameras, acquisition parameters);Limits of the acquisition and uncertainty of the measure;New acquisition technologies The proposed discussion gives basic and advanced considerations to improve the quality of the processing results and images obtained can be elaborated with different processing algorithms
Feasibility Study of Drone-Based 3-D Measurement of Defects in Concrete Structures
Full text linkRecognition of defects in concrete structures, identification of cracks, concrete spalling, or other geometrical defects are important tools for structural damage detection. Defects in structures can include cracks, but also missing parts, due to the wear caused by weather or aging phenomena. These last types of defects in structures can be identified using red-green-blue (RGB) cameras, but the level of damage could be difficult to evaluate with 2-D images. In this sense, the application of 3-D reconstruction techniques can be helpful to determine the 3-D dimensions of spalling, swelling of concrete or the presence of visible steel parts of reinforced concrete. The use of drones for this type of measurement is very attractive for reducing the costs and time of measurement campaigns. However, the lack of accurate trajectory information and the vibrations affect the accuracy of 3-D measurements. In this article, a metrological characterization of measurement systems for the evaluation and recognition of defects in concrete structures is presented, starting from the acquisition of 3-D point clouds by low-cost time-of-flight (ToF) sensors, placed on drones. To evaluate the uncertainty of these systems, a mock-up with realistic defects was developed and characterized using a reference 3-D scanner. The 3-D reconstructions obtained via the selected sensors were used to evaluate the discrepancies of the 3-D shape compared to a ground truth model and the uncertainty of the selected scanners. The results show that, for all the defects tested, the standard deviation of the discrepancies between the defect reconstructed using the drone and the ground truth is below 2.5 mm
Uncertainty mitigation in drone-based 3D scanning of defects in concrete structures
No full textThe measurement of defects in a concrete structures is highly relevant to determine how maintenance interventions should be performed. However, it could be difficult and potentially dangerous to inspect a certain structure by bringing trained operators, to places that are difficult to access. This issue could be overcome by framing the parts of interest of a building with a drone equipped with cameras. Nonetheless, a quantitative measure of a defect cannot be obtained with 2D cameras, since the pixel to millimeters scale and the estimation of depth are missing. To obtain a 3D shape measurement of a defect, 3D scanners, joined with 3D reconstruction, could be applied. In this article, we present a metrological evaluation of low-cost Time-Of-Flight (ToF) sensors for defects in concrete structures measurement. The defects of interest for this class of 3D scanners are mainly related to concrete spalling. This type of scanners was assembled on a drone with an onboard acquisition system. The testing benchmark for this study is based on a real structure with concrete spalling defects. A ground truth 3D model was obtained with a high-precision 3D scanner, used with a scaffolding. The effect of disturbances on measures were investigated, as well. The results of drone tests show that the systematic error of the 3D reconstruction with the selected sensors is about 0.5-2 mm, with a dispersion of raw data around the 3D reconstruction of about 2-4.5 mm, at a distance from the target of about 1.8-2 m
Il contributo di Gino Zappa e di Alberto Ceccherelli allo sviluppo dell’informativa contabile
No full textIl lavoro intende mettere in evidenza il contributo fornito da Gino Zappa e da Alberto Ceccherelli allo sviluppo della normativa sul bilancio di esercizio
Il contributo di Gino Zappa e di Alberto Ceccherelli allo sviluppo dell’informativa contabile
No full textIl lavoro intende mettere in evidenza il contributo fornito da Gino Zappa e da Alberto Ceccherelli allo sviluppo della normativa sul bilancio di esercizio
Duccio Balestracci, La zappa e la retorica. Memorie familiari di un contadino toscano del quattrocento
No full textRedon Odile. Duccio Balestracci, La zappa e la retorica. Memorie familiari di un contadino toscano del quattrocento. In: Annales. Economies, sociétés, civilisations. 41ᵉ année, N. 1, 1986. pp. 167-168
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