Determination of Maximum Accuracy of Concrete Textures as Natural Targets for Movement Tracking Through DIC

The use of natural targets is one of the obstacles to the extensive use of digital image cross-correlation for measuring movements in civil structures. Long distance measurement through image and without access to the structure itself, brings results in an improvement in accessibility, being the procedure cheaper and safer than common methods that require direct access to the measuring point. One of the most used materials in construction is concrete. Therefore, it is important to analyze its performance when using image cross-correlation. In this work, we have made a series of concrete probes with different production characteristics to have a representative variety of concrete surfaces. With them, we have studied their floor error in a cross-correlation procedure using different illumination and blur conditions, to evaluate the influence of those parameters on the results. All results are compared to those obtained using the conventional texture for image cross-correlation techniques, that is a pseudo-speckle target. All experiments are done in laboratory conditions to control all variables involved and to avoid the influence of other variables linked to open air conditions, such as atmospheric disturbances. As a result, we have determined the best conditions to use the natural concrete texture and we have quantified that using this texture leads to a decrease in the accuracy of the results from two to three times the one obtained with a typical pseudo-speckle texture.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research was done with the financial support of the Spanish Ministry of Science and Innovation through the project PID2021-126485OB-I00 in which all authors are involved

Use of Image Correlation to Measure Macroscopic Strains by Hygric Swelling in Sandstone Rocks

Some materials undergo hygric expansion when soaked. In porous rocks, this effect is enhanced by the pore space, because it allows water to reach every part of its volume and to hydrate most swelling parts. In the vicinity, this enlargement has negative structural consequences as adjacent elements support some compressions or displacements. In this work, we propose a normalized cross-correlation between rock surface texture images to determine the hygric expansion of such materials. We used small porous sandstone samples (11 × 11 × 30 mm3) to measure hygric swelling. The experimental setup comprised an industrial digital camera and a telecentric objective. We took one image every 5 min for 3 h to characterize the whole swelling process. An error analysis of both the mathematical and experimental methods was performed. The results showed that the proposed methodology provided, despite some limitations, reliable hygric swelling information by a non-contact methodology with an accuracy of 1 micron and permitted the deformation in both the vertical and horizontal directions to be explored, which is an advantage over traditional linear variable displacement transformers.This research was funded by the Generalitat Valenciana and the European Social Fund (FSE) through the Recruitment of Predoctoral Research Staff ACIF/2018/211 included in the FSE Operational Program 2014–2020 of the Valencian Community (Spain). Belén Ferrer and María-Baralida Tomás acknowledge the support from the Generalitat Valenciana through Project GV/2020/077

Analizando el sesgo implícito de género en Óptica y Fotónica en la etapa predoctoral en España

Gender biases play a very significant role in areas related to science, technology, engineering, and mathematics (STEM). The association of gender with certain attributes, behaviors or professions leads to a lower proportion of women in STEM. In the field of Optics and Photonics, we can identify a gender disparity between technical or bio-clinical approaches within the same area when examining the authorship of the defended thesis. In this work, we quantify the impact of implicit gender bias in the Ph.D. programs related to Optics and Photonics in Spain. Here we present an exhaustive study about the UNESCO descriptors of the theses defended within 2015-2020 through the open-access repository TESEO, where all the doctoral theses of Spanish universities are compiled. The doctorate program of each thesis is considered and classified into a technical or bio-clinical category. With this classification, we quantify the number of male and female authors within each category, and the results show up a clear unbalance in most of the evaluated descriptors: men are more likely to choose technical doctorate programs, while women are mostly present in clinical or biological programs. This difference is seen even in descriptors where both genders are equally represented. On one side, women’s underrepresentation is higher in “Physics”, “Astronomy and Astrophysics”, “Earth and Space Sciences”, and “Technological Sciences”. Oppositely, the areas of “Chemistry”, “Life Sciences”, and “Medical Sciences” show a greater gender-balanced distribution for most of the descriptors.Los prejuicios de género desempeñan un papel muy importante en áreas relacionadas con la ciencia, la tecnología, la ingeniería y las matemáticas (STEM). La asociación del género con determinados atributos, comportamientos o profesiones conduce a una menor proporción de mujeres en STEM. En el campo de la Óptica y la Fotónica, podemos identificar una disparidad de género entre enfoques técnicos o bioclínicos dentro de la misma área al examinar la autoría de la tesis defendida. En este trabajo, cuantificamos el impacto del sesgo implícito de género en los programas de doctorado relacionados con la Óptica y Fotónica en España. Aquí presentamos un estudio exhaustivo sobre los descriptores UNESCO de las tesis defendidas en el periodo 2015-2020 a través del repositorio de acceso abierto TESEO, donde se recopilan todas las tesis doctorales de las universidades españolas. Se considera el programa de doctorado de cada tesis y se clasifica en una categoría técnica o bioclínica. Con esta clasificación, cuantificamos el número de autores y autoras dentro de cada categoría, y los resultados muestran un claro desequilibrio en la mayoría de los descriptores evaluados: los hombres son más propensos a elegir programas de doctorado técnicos, mientras que las mujeres están mayoritariamente presentes en programas clínicos o biológicos. Esta diferencia se observa incluso en los descriptores en los que ambos sexos están representados por igual. Por un lado, la infrarrepresentación femenina es mayor en "Física", "Astronomía y Astrofísica", "Ciencias de la Tierra y del Espacio" y "Ciencias Tecnológicas". Por el contrario, las áreas de "Química", "Ciencias de la Vida" y "Ciencias Médicas" muestran una distribución más equilibrada entre hombres y mujeres en la mayoría de los descriptores

Influence of Neighborhood Size and Cross-Correlation Peak-Fitting Method on Location Accuracy

Figures, results and programs in Matlab format available in http://hdl.handle.net/10045/110141A known technique to obtain subpixel resolution by using object tracking through cross-correlation consists of interpolating the obtained correlation function and then refining peak location. Although the technique provides accurate results, peak location is usually biased toward the closest integer coordinate. This effect is known as the peak-locking error and it strongly limits this calculation technique’s experimental accuracy. This error may differ depending on the scene and algorithm used to fit and interpolate the correlation peak, but in general, it may be attributed to a sampling problem and the presence of aliasing. Many studies in the literature analyze this effect in the Fourier domain. Here, we propose an alternative analysis on the spatial domain. According to our interpretation, the peak-locking error may be produced by a non-symmetrical sample distribution, thus provoking a bias in the result. According to this, the peak interpolant function, the size of the local domain and low-pass filters play a relevant role in diminishing the error. Our study explores these effects on different samples taken from the DIC Challenge database, and the results show that, in general, peak fitting with a Gaussian function on a relatively large domain provides the most accurate results.This work has been supported by the Generalitat Valenciana and the European Social Fund (FSE) through the Recruitment of Predoctoral Research Staff ACIF/2018/211 included in the FSE Operational Program 2014–2020 of the Valencian Community. Belén Ferrer and María-Baralida Tomás acknowledge the support of the Generalitat Valenciana through Project GV/2020/077

Use of image correlation to measure hygric swelling in rocks

Some materials undergo an hygric expansion when they are soaked. In porous rocks, this effect is enhanced by the pore space that allows the water to reach every part of its volume and to hydrate the most of their swelling parts. This enlargement has negative structural consequences in the vicinity since adjacent elements will support some compressions or displacements. Recently image-based methods have arisen in this field due to their advantages versus traditional methods. Among all image processing methods, digital image correlation (DIC) is one of the most used in all areas. In this work, we propose a new methodology based on DIC for the calculation of the hygric expansion of materials. We use porous sandstone, with dimensions 14x14x30 mm to measure its hygric swelling using an industrial digital camera and a telecentric objective. We took one image every 5 minutes to characterize the whole swelling process. Due the large magnification, the whole 14 mm length of one contour was not in the image and therefore we lost the image scale reference. To solve this, a 1951 USAF test was used to calibrate the imagen. The telecentric objective and a narrow deep of field allowed to have the specimen surface exactly on the same plane that the USAF test was during the calibration. The image was pointed to one corner of the specimen, to obtain information not only of its vertical displacement due to its expansión but also of its horizontal movement. Preliminary results show that the proposed methodology provides reliable information of the hygric swelling using a non-contact methodology, with an accuracy of 1 micron.This work has been supported by the Generalitat Valenciana and the European Social Fund (FSE) through the Recruitment of Predoctoral Research Staff ACIF/2018/211 included in the FSE Operational Program 2014-2020 of the Valencian Community

Influence of Neighborhood Size and Cross-Correlation Peak-Fitting Method on Location Accuracy [Figures, results and programs]

Figures, results and programs in Matlab format. Paper available in http://hdl.handle.net/10045/110428A known technique to obtain subpixel resolution by using object tracking through cross-correlation consists of interpolating the obtained correlation function and then refining peak location. Although the technique provides accurate results, peak location is usually biased toward the closest integer coordinate. This effect is known as the peak-locking error and it extremely limits this calculation technique’s experimental accuracy. This error may differ depending on the scene and algorithm used to fit and interpolate the correlation peak, but in general, may be attributted to an sampling problem and the presence of aliasing. Many studies in the literature analyze this effect in the Fourier domain. Here we propose an alternative analysis on the spatial domain. According to our interpretation, peak locking error may be produced by a non-symmetrical sample distribution thus provoking a bias in the result. According to this, the peak interpolant function, the size of the local domain and low pass filters play a relevant role in diminishing the error. Our study explores these effects on different samples taken from the DIC Challenge database, and the results show that, in general peak fitting with a Gaussian function on a relatively large domain provides the most accurate results