Development of a Computer Vision-Based Three-Dimensional Reconstruction Method for Volume-Change Measurement of Unsaturated Soils during Triaxial Testing

Problems associated with unsaturated soils are ubiquitous in the U.S., where expansive and collapsible soils are some of the most widely distributed and costly geologic hazards. Solving these widespread geohazards requires a fundamental understanding of the constitutive behavior of unsaturated soils. In the past six decades, the suction-controlled triaxial test has been established as a standard approach to characterizing constitutive behavior for unsaturated soils. However, this type of test requires costly test equipment and time-consuming testing processes. To overcome these limitations, a photogrammetry-based method has been developed recently to measure the global and localized volume-changes of unsaturated soils during triaxial test. However, this method relies on software to detect coded targets, which often requires tedious manual correction of incorrectly coded target detection information. To address the limitation of the photogrammetry-based method, this study developed a photogrammetric computer vision-based approach for automatic target recognition and 3D reconstruction for volume-changes measurement of unsaturated soils in triaxial tests. Deep learning method was used to improve the accuracy and efficiency of coded target recognition. A photogrammetric computer vision method and ray tracing technique were then developed and validated to reconstruct the three-dimensional models of soil specimen

Airborne LiDAR for DEM generation: some critical issues

Airborne LiDAR is one of the most effective and reliable means of terrain data collection. Using LiDAR data for DEM generation is becoming a standard practice in spatial related areas. However, the effective processing of the raw LiDAR data and the generation of an efficient and high-quality DEM remain big challenges. This paper reviews the recent advances of airborne LiDAR systems and the use of LiDAR data for DEM generation, with special focus on LiDAR data filters, interpolation methods, DEM resolution, and LiDAR data reduction. Separating LiDAR points into ground and non-ground is the most critical and difficult step for DEM generation from LiDAR data. Commonly used and most recently developed LiDAR filtering methods are presented. Interpolation methods and choices of suitable interpolator and DEM resolution for LiDAR DEM generation are discussed in detail. In order to reduce the data redundancy and increase the efficiency in terms of storage and manipulation, LiDAR data reduction is required in the process of DEM generation. Feature specific elements such as breaklines contribute significantly to DEM quality. Therefore, data reduction should be conducted in such a way that critical elements are kept while less important elements are removed. Given the highdensity characteristic of LiDAR data, breaklines can be directly extracted from LiDAR data. Extraction of breaklines and integration of the breaklines into DEM generation are presented

Virtual geological outcrops - fieldwork and analysis made less exhaustive?

For geologists studying outcrops in the field, there is an ever‐increasing need for the acquisition of accurate and comprehensive data, whatever their purpose. Fortunately, this need is mirrored by an expanding range of digital data capturing technologies that provide the possibility of examining geological outcrops in minute detail from the desktop. Although difficult technologically, there is also a need to combine differing datasets into a single, accurate, digital model that will allow field geologists to place their data in a wider context. This paper examines the techniques available, and highlights new Light Detection and Ranging (LIDAR) technology which should prove to be a unifying technique, being able to combine images and local coordinates on‐site

OPEN SOURCE WEB TOOL FOR TRACKING IN A LOWCOST MOBILE MAPPING SYSTEM

During the last decade several Mobile Mapping Systems (MMSs), i.e. systems able to acquire efficiently three dimensional data using moving sensors (Guarnieri et al., 2008, Schwarz and El-Sheimy, 2004), have been developed. Research and commercial products have been implemented on terrestrial, aerial and marine platforms, and even on human-carried equipment, e.g. backpack (Lo et al., 2015, Nex and Remondino, 2014, Ellum and El-Sheimy, 2002, Leica Pegasus backpack, 2016, Masiero et al., 2017, Fissore et al., 2018).<br><br> Such systems are composed of an integrated array of time-synchronised navigation sensors and imaging sensors mounted on a mobile platform (Puente et al., 2013, Tao and Li, 2007). Usually the MMS implies integration of different types of sensors, such as GNSS, IMU, video camera and/or laser scanners that allow accurate and quick mapping (Li, 1997, Petrie, 2010, Tao, 2000). The typical requirement of high-accuracy 3D georeferenced reconstruction often makes such systems quite expensive. Indeed, at time of writing most of the terrestrial MMSs on the market have a cost usually greater than 50000, which might be expensive for certain applications (Ellum and El-Sheimy, 2002, Piras et al., 2008). In order to allow best performance sensors have to be properly calibrated (Dong et al., 2007, Ellum and El-Sheimy, 2002).<br><br> Sensors in MMSs are usually integrated and managed through a dedicated software, which is developed ad hoc for the devices mounted on the mobile platform and hence tailored for the specific used sensors. Despite the fact that commercial solutions are complete, very specific and particularly related to the typology of survey, their price is a factor that restricts the number of users and the possible interested sectors.<br><br> This paper describes a (relatively low cost) terrestrial Mobile Mapping System developed at the University of Padua (TESAF, Department of Land Environment Agriculture and Forestry) by the research team in CIRGEO, in order to test an alternative solution to other more expensive MMSs. The first objective of this paper is to report on the development of a prototype of MMS for the collection of geospatial data based on the assembly of low cost sensors managed through a web interface developed using open source libraries. The main goal is to provide a system accessible by any type of user, and flexible to any type of upgrade or introduction of new models of sensors or versions thereof. After a presentation of the hardware components used in our system, a more detailed description of the software developed for the management of the MMS will be provided, which is the part of the innovation of the project. According to the worldwide request for having big data available through the web from everywhere in the world (Pirotti et al., 2011), the proposed solution allows to retrieve data from a web interface Figure 4. Actually, this is part of a project for the development of a new web infrastructure in the University of Padua (but it will be available for external users as well), in order to ease collaboration between researchers from different areas.<br><br> Finally, strengths, weaknesses and future developments of the low cost MMS are discussed

A new digital image correlation software for displacements field measurement in structural applications

Recently, there has been a growing interest in studying non-contact techniques for strain and displacement measurement. Within photogrammetry, Digital Image Correlation (DIC) has received particular attention thanks to the recent advances in the field of low-cost, high resolution digital cameras, computer power and memory storage. DIC is indeed an optical technique able to measure full field displacements and strain by comparing digital images of the surface of a material sample at different stages of deformation and thus can play a major role in structural monitoring applications. For all these reasons, a free and open source 2D DIC software, named py2DIC, was developed at the Geodesy and Geomatics Division of DICEA, University of Rome "La Sapienza". Completely written in python, the software is based on the template matching method and computes the displacement and strain fields. The potentialities of Py2DIC were evaluated by processing the images captured during a tensile test performed in the Lab of Structural Engineering, where three different Glass Fiber Reinforced Polymer samples were subjected to a controlled tension by means of a universal testing machine. The results, compared with the values independently measured by several strain gauges fixed on the samples, demonstrate the possibility to successfully characterize the deformation mechanism of the investigated material. Py2DIC is indeed able to highlight displacements at few microns level, in reasonable agreement with the reference, both in terms of displacements (again, at few microns in the average) and Poisson's module

Progress in industrial photogrammetry by means of markerless solutions

174 p.La siguiente tesis está enfocada al desarrollo y uso avanzado de metodologías fotogramétrica sin dianas en aplicaciones industriales. La fotogrametría es una técnica de medición óptica 3D que engloba múltiples configuraciones y aproximaciones. En este estudio se han desarrollado procedimientos de medición, modelos y estrategias de procesamiento de imagen que van más allá que la fotogrametría convencional y buscan el emplear soluciones de otros campos de la visión artificial en aplicaciones industriales. Mientras que la fotogrametría industrial requiere emplear dianas artificiales para definir los puntos o elementos de interés, esta tesis contempla la reducción e incluso la eliminación de las dianas tanto pasivas como activas como alternativas prácticas. La mayoría de los sistemas de medida utilizan las dianas tanto para definir los puntos de control, relacionar las distintas perspectivas, obtener precisión, así como para automatizar las medidas. Aunque en muchas situaciones el empleo de dianas no sea restrictivo existen aplicaciones industriales donde su empleo condiciona y restringe considerablemente los procedimientos de medida empleados en la inspección. Un claro ejemplo es la verificación y control de calidad de piezas seriadas, o la medición y seguimiento de elementos prismáticos relacionados con un sistema de referencia determinado. Es en este punto donde la fotogrametría sin dianas puede combinarse o complementarse con soluciones tradicionales para tratar de mejorar las prestaciones actuales

PHOTOGRAMMETRIC APPROACH IN DETERMINING BEAM-COLUMN CONNECTION DEFORMATIONS

In accordance with the advances in technology, displacement calculation techniquesare ever developing. Photogrammetry has become preferable in some newdisciplines with the advances in the image processing methods. In this study, theauthors have used two different measurement techniques to determine the angles ofrotation in beam-column connections that are subjected to reversible cyclic loading.The first of these is the method that is widely used, the conventional method instructural mechanics experiments, where Linear Variable Differential Transformers(LVDTs) are utilized; and the second is the photogrammetric measurementtechnique. The rotation angles were determined using these techniques in a total often steel beam-column connection experiments. After discussing the test proceduresof the aforementioned methods, the results were presented. It was observed that therotation angles measured by each method were very close to each other. It wasconcluded that the photogrammetric measurement technique could be used as analternative to conventional methods, where electronic LVDTs are used