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geometrical calibration

Mahdi Rezapour, Milhan Moomen, Khaled Ksaibati
INTRODUCTION: The state of Wyoming, like other western United States, is characterized by mountainous terrain. Such terrain is well noted for its severe downgrades and difficult geometry. Given the specific challenges of driving in such difficult terrain, crashes with severe injuries are bound to occur. The literature is replete with research about factors that influence crash injury severity under different conditions. Differences in geometric characteristics of downgrades and mechanics of vehicle operations on such sections mean different factors may be at play in impacting crash severity in contrast to straight, level roadway sections...
February 2019: Journal of Safety Research
Xueyang Xu, Xiangchao Zhang, Zhenqi Niu, Wei Wang, Yifan Zhu, Min Xu
Accurate in situ measurement of complex optical surfaces is desired for precision manufacturing, and deflectometry is a promising measuring method. However, deflectometry's measurement accuracy depends heavily on the geometric calibration's reliability. Existing calibration methods suffer from the limitations of low efficiency, complicated operations, and expensive equipment. Therefore, a self-calibration method is proposed for the monoscopic deflectometry in order to determine the the camera and screen positions...
March 4, 2019: Optics Express
Xingpeng Yan, Jun Wen, Zhiqiang Yan, Teng Zhang, Xiaoyu Jiang
Three-dimensional display with large-format is an inevitable and foreseeable trend for the future display technology, integral imaging is one of the most powerful and promising candidates to achieve this goal with full-parallax, true-color, acceptable viewing resolution and viewing angle. To obtain a 3D display with high quality, calibration is needed to correct optical misalignment and optical aberrations, which is often challenging and time consuming. We propose a post-calibration compensation method for the integral imaging system with macrolens array, the inter-lens position misalignment is corrected by forcing it to image in a regular ideal reference grid...
February 18, 2019: Optics Express
Gaopeng Zhang, Hong Zhao, Hongtao Yang, Yang Hong, Yueyang Ma, Feifei Gu
For the on-orbit space zoom camera, the camera focal length is in a constant process of change; accordingly, compared with calibrating other camera intrinsic parameters, calibrating the focal length has a practical significance for the space zoom camera. With the vanishing points obtained from the solar panel of human-made space satellites, this paper introduces a focal length self-calibration method for the on-orbit space zoom camera. First, the geometrical relationship and infinite homography of vanishing points at various camera positions are used to derive the method...
February 20, 2019: Applied Optics
Shanshan Lv, Mingshun Jiang, Chenhui Su, Lei Zhang, Faye Zhang, Qingmei Sui, Lei Jia
This publisher's note amends the Funding section of Appl. Opt.58, A7 (2019)APOPAI0003-693510.1364/AO.58.0000A7.
February 10, 2019: Applied Optics
Shanshan Lv, Mingshun Jiang, Chenhui Su, Lei Zhang, Faye Zhang, Qingmei Sui, Lei Jia
Fringe projection profilometry (FPP) technology is an important method for 3D reconstruction. In this paper, we proposed a flexible calibration method of an FPP system based on the imaging principle and geometrical structure of the system. The target coordinates are only related to its pixel coordinates and phase. First, the fringe images are projected onto the calibration plate, and the phase can be calculated through the four-step phase-shifting method. Then, the pixel coordinates of the feature points can be located with the binarized fringe images and the centroid method...
February 10, 2019: Applied Optics
G Pietrzyński, D Graczyk, A Gallenne, W Gieren, I B Thompson, B Pilecki, P Karczmarek, M Górski, K Suchomska, M Taormina, B Zgirski, P Wielgórski, Z Kołaczkowski, P Konorski, S Villanova, N Nardetto, P Kervella, F Bresolin, R P Kudritzki, J Storm, R Smolec, W Narloch
In the era of precision cosmology, it is essential to determine the Hubble constant empirically with an accuracy of one per cent or better1 . At present, the uncertainty on this constant is dominated by the uncertainty in the calibration of the Cepheid period-luminosity relationship2,3 (also known as the Leavitt law). The Large Magellanic Cloud has traditionally served as the best galaxy with which to calibrate Cepheid period-luminosity relations, and as a result has become the best anchor point for the cosmic distance scale4,5 ...
March 2019: Nature
Yekutiel Katz, Gal Dahan, Jacob Sosna, Ilan Shelef, Evgenia Cherniavsky, Zohar Yosibash
Patient-specific QCT-based finite element (QCTFE) analyses enable highly accurate quantification of bone strength. We evaluated CT scanner influence on QCTFE models of long bones. A femur, humerus, and proximal femur without the head were scanned with K2 HPO4 phantoms by seven CT scanners (four models) using typical clinical protocols. QCTFE models were constructed. The geometrical dimensions, as well as the QCT-values expressed in Hounsfield unit (HU) distribution was compared. Principal strains at representative regions of interest (ROIs), and maximum principal strains (associated with fracture risk) were compared...
February 12, 2019: Journal of Biomechanics
Malakeh Malekzadeh, Shahrokh Abbasi-Rad, Mohamad Shahgholi, Parisa Naghdi, Marzieh Sadat Hoseini, Niloofar Ayoobi Yazdi, Mohammad Bagher Shiran, Hamidreza Saligheh Rad
INTRODUCTION: Quantitative computed tomography (QCT) can supplement dual x-ray absorptiometry by enabling geometric and compartmental bone assessments. Whole-body spiral CT scanners are widely available and require a short scanning time of seconds, in contrast to peripheral QCT scanners, which require several minutes of scanning time. This study designed and evaluated the accuracy and precision of a homemade QCT calibration phantom using a whole-body spiral CT scanner. MATERIALS AND METHODS: The QCT calibration phantom consisted of K2 HPO4 solutions as reference...
March 2019: Journal of Medical Imaging and Radiation Sciences
Barbara Carl, Miriam Bopp, Benjamin Voellger, Benjamin Saß, Christopher Nimsky
OBJECTIVE: To investigate how augmented reality (AR) can be applied to support transsphenoidal surgery. METHODS: AR was established using the head-up displays integrated into operating microscopes. Navigation registration was performed either fiducial-based or by automatic registration applying intraoperative computed tomography (iCT). Correct microscope calibration was ensured by checking the geometric overlap between the AR representation of the reference array and 3-D reality while focusing on the reference array...
February 11, 2019: World Neurosurgery
Xiao Li, Wei Liu, Yi Pan, Jianwei Ma, Fuji Wang
Periodic health checks of contouring errors under unloaded conditions are critical for machine performance evaluation and value-added manufacturing. Aiming at breaking the dimension, range and speed measurement limitations of the existing devices, a cost-effective knowledge-driven approach for detecting error motions of arbitrary paths using a single camera is proposed. In combination with the PNP algorithm, the three-dimensional (3D) evaluation of large-scale contouring error in relatively high feed rate conditions can be deduced from a priori geometrical knowledge...
February 12, 2019: Sensors
Zhangji Lu, Lilong Cai
In this paper, we realize an accurate and flexible measurement method for paraxial focal length with a simple apparatus. The proposed method utilizes the established measurement principle which is based on the differentiation of the Gaussian optical formula and geometrical relationship of camera-lens system to obtain the focal length of a lens. Some image processing methods are employed to experimentally realize this measurement principle with high accuracy and practicability. Image sharpness evaluation function is utilized to ensure the system conforms to the Gaussian optical formula...
February 4, 2019: Optics Express
Charles Vanwynsberghe, Pascal Challande, François Ollivier, Jacques Marchal, Régis Marchiano
Large microphone arrays are an efficient means for source localization thanks to a wide aperture and a great number of sensors. When such arrays are deployed in situ, accurate geometric calibration becomes essential to obtain the microphone positions. In free field, the classic procedures rely on measured Times of Arrival (TOA) or Time Differences of Arrival (TDOA) between the microphones and several controlled sources. However, free field model mismatches, such as reflectors, generate outliers which severely deteriorate the positioning accuracy...
January 2019: Journal of the Acoustical Society of America
Yingdong Pi, Bo Yang, Xin Li, Mi Wang
We conducted a systematic investigation into independent on-orbit geometric calibration, with the aim of applying it to linear agile optical satellite (AOS). Using a combination of multi-attitude images, a complete full-link independent calibration method chain was achieved, in which both the internal and external systematic parameters could be calibrated using the self-constraint of these images, as distinct from the absolute constraints identified from ground calibration sites. In accordance with the capacity for restraint associated with the self-constraint of the images and the geometric characteristics of the systematic errors in the imaging model, the calibration parameters that were deemed suitable for mathematical estimation under this self-constraint, as well as capable of compensating for the systematic errors, were determined by two equivalent compensations...
January 21, 2019: Optics Express
Shinichiro Mori, Yukinobu Sakata, Ryusuke Hirai, Wataru Furuichi, Kazuki Shimabukuro, Ryosuke Kohno, Woong Sub Koom, Shigeru Kasai, Keiko Okaya, Yasushi Iseki
PURPOSE: To perform the final quality assurance of our fluoroscopic-based markerless tumor tracking for gated carbon-ion pencil beam scanning (C-PBS) radiotherapy using a rotating gantry system, we evaluated the geometrical accuracy and tumor tracking accuracy using a moving chest phantom with simulated respiration. METHODS: The positions of the dynamic flat panel detector (DFPD) and X-ray tube are subject to changes due to gantry sag. To compensate for this, we generated a geometrical calibration table (gantry flex map) in 15° gantry angle steps by the bundle adjustment method...
January 28, 2019: Medical Physics
Giovanni Caruso, Pablo J Zarco-Tejada, Victoria González-Dugo, Marco Moriondo, Letizia Tozzini, Giacomo Palai, Giovanni Rallo, Alberto Hornero, Jacopo Primicerio, Riccardo Gucci
The experiments were conducted in a fully-productive olive orchard (cv. Frantoio) at the experimental farm of University of Pisa at Venturina (Italy) in 2015 to assess the ability of an unmanned aerial vehicle (UAV) equipped with RGB-NIR cameras to estimate leaf area index (LAI), tree height, canopy diameter and canopy volume of olive trees that were either irrigated or rainfed. Irrigated trees received water 4-5 days a week (1348 m3 ha-1), whereas the rainfed ones received a single irrigation of 19 m3 ha-1 to relieve the extreme stress...
2019: PloS One
Akito Saito, Atsuyuki Ohashi, Teiji Nishio, Daiki Hashimoto, Hidemasa Maekawa, Yuji Murakami, Shuichi Ozawa, Makiko Suitani, Masato Tsuneda, Koji Ikenaga, Yasushi Nagata
PURPOSE: A patient's respiratory monitoring is one of the key techniques in radiotherapy for a moving target. Generally, such monitoring systems are permanently set to a fixed geometry during the installation. This study aims to enable a temporary setup of such a monitoring system by developing a fast method to automatically calibrate the geometrical position by a quick measurement of calibration markers. METHODS: One calibration marker was placed on the isocenter and the other six markers were placed at positions 5-cm apart from the isocenter to the left, right, anterior, posterior, superior, and inferior directions...
January 8, 2019: Medical Physics
Petr Bouchal, Petr Dvorak, Jiri Babocky, Zdenek Bouchal, Filip Ligmajer, Martin Hrtoň, Vlastimil Křápek, Alexander Faßbender, Stefan Linden, Radim Chmelik, Tomas Sikola
Optical metasurfaces have emerged as a new generation of building blocks for multi-functional optics. Design and realization of metasurface elements place ever-increasing demands on accurate assessment of phase alterations introduced by complex nanoantenna arrays, a process referred to as quantitative phase imaging. Despite considerable effort, the widefield (non-scanning) phase imaging that would approach resolution limits of optical microscopy and indicate the response of a single nanoantenna still remains a challenge...
January 2, 2019: Nano Letters
Pedro Luiz Coelho Rodrigues, Christian Jutten, Marco Congedo
OBJECTIVE: This paper presents a Transfer Learning approach for dealing with the statistical variability of EEG signals recorded on different sessions and/or from different subjects. This is a common problem faced by Brain-Computer Interfaces (BCI) and poses a challenge for systems that try to reuse data from previous recordings to avoid a calibration phase for new users or new sessions for the same user. METHOD: We propose a method based on Procrustes analysis for matching the statistical distributions of two datasets using simple geometrical transformations (translation, scaling and rotation) over the data points...
December 25, 2018: IEEE Transactions on Bio-medical Engineering
Michael D Burns, Brian L Sidlauskas
The characiform fishes of the Neotropics and Africa radiated remarkably in ecomorphology, but the macroevolutionary processes responsible for their biodiversity remain unexplored, and the degree to which their continental diversification parallels classic adaptive radiations remains untested. We reconstruct their diversification using a new fossil-calibrated molecular phylogeny, dietary information, and geometric morphometrics. Though body shape diversified early in a manner consistent with an ancient continental adaptive radiation, trophic shifts did not always coincide with shape changes...
December 18, 2018: Evolution; International Journal of Organic Evolution
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