Search

This paper presents a novel geometric calibration method for focused light field camera to trace the rays of flame radiance and to reconstruct the three-dimensional (3-D) temperature distribution of a flame. A calibration model is developed to calculate the corner points and their projections of the focused light field camera. The characteristics of matching main lens and microlens f-numbers are used as an additional constrains for the calibration. Geometric parameters of the focused light field camera are then achieved using Levenberg-Marquardt algorithm. Total focused images in which all the points are in focus, are utilized to validate the proposed calibration method. Calibration results are presented and discussed in details. The maximum mean relative error of the calibration is found less than 0.13%, indicating that the proposed method is capable of calibrating the focused light field camera successfully. The parameters obtained by the calibration are then utilized to trace the rays of flame radiance. A least square QR-factorization algorithm with Plank's radiation law is used to reconstruct the 3-D temperature distribution of a flame. Experiments were carried out on an ethylene air fired combustion test rig to reconstruct the temperature distribution of flames. The flame temperature obtained by the proposed method is then compared with that obtained by using high-precision thermocouple. The difference between the two measurements was found no greater than 6.7%. Experimental results demonstrated that the proposed calibration method and the applied measurement technique perform well in the reconstruction of the flame temperature. [ABSTRACT FROM AUTHOR]

Three-dimensional reconstruction of vessels from digital X-ray angiographic images is a powerful technique that compensates for limitations in angiography. It can provide physicians with the ability to accurately inspect the complex arterial network and to quantitatively assess disease induced vascular alterations in three dimensions. In this paper, both the projection principle of single view angiography and mathematical modeling of two view angiographies are studied in detail. The movement of the table, which commonly occurs during clinical practice, complicates the reconstruction process. On the basis of the pinhole camera model] and existing optimization methods, an algorithm is developed for 3-D reconstruction of coronary arteries from two uncalibrated monoplane angiographic images. A simple and effective perspective projection model is proposed for the 3-D reconstruction of coronary arteries. A nonlinear optimization method is employed for refinement of the 3-D structure of the vessel skeletons, which takes the influence of table movement into consideration. An accurate model is suggested for the calculation of contour points of the vascular surface, which fully utilizes the information in the two projections. In our experiments with phantom and patient angiograms, the vessel centerlines are reconstructed in 3-D space with a mean positional accuracy of 0.665 mm and with a mean back projection error of 0.259 mm. This shows that the algorithm put forward in this paper is very effective and robust. [ABSTRACT FROM AUTHOR]

3-D characteristics of bubbles are of great importance to understand the flow mechanism in bubbly flows. A complete matching method based on virtual stereo vision is presented in this paper, and 3-D motion parameters are reconstructed. According to the captured images of multiple bubbles from two virtual views, a series of image processing steps are designed to extract the feature parameters of bubbles for the following work. To establish the correspondence relationship of the identical bubble from the two half images, a stereo matching method based on a multivariable constrained threshold is proposed to figure out the identical bubble from two views. On this base, a 3-D polar coordinate homonymy correlation algorithm is developed to keep the correspondence of the multibubbles from successive frames. Combined with the calibration, 3-D multibubble trajectories and velocities are then reconstructed effectively. The reconstruction accuracy of the measurement distance between the bubbles is finally verified by capturing the image of the calibration reference. The results show that the stereo matching method and the tracking algorithm of bubbles are valid, and with high precision. [ABSTRACT FROM PUBLISHER]

Three-dimensional measurement of shiny or reflective surface is a challenging issue for optical-based instrumentations. In this paper, we present a novel structured light approach for direct measurement of shiny target so as to skip the coating preprocedure. In comparison with traditional image-intensity-based structured light coding strategies like sinusoidal and line patterns, strip edges not raw image intensities are encoded in the illuminated patterns. With strip edges generally better preserved than individual image intensity in the image data in the presence of surface reflections, such a coding strategy is more robust. To remove the periodic ambiguity within strip patterns, traditional Gray code patterns are adopted. To localize the strip edges more precisely, both positive and negative strip patterns are used. An improved zero-crossing feature detector that has subpixel accuracy is proposed for strip-edge localization. The experimental setup is configured with merely an off-the-shelf pico-projector and a camera. Extensive experiments including accuracy evaluation, comparison with previous structured light algorithms, and the reconstruction of some real shiny objects are shown to demonstrate the system's accuracy and endurance against reflective nature of surfaces. [ABSTRACT FROM PUBLISHER]

In this paper, a new technology which can be used to diagnose 3-D temperature distribution of argon arc plasma is proposed. Compared with current technologies, two aspects have been improved. First, a new hybrid reconstruction technique [max-entropy, least square, and flatness reconstruction technique (MLFRT)] is presented as an algorithm system, where the numerical simulation of the MLFRT has been realized. The results show that the MLFRT has good convergence, stability, and efficiency. Second, two orthographic double-wavelength light paths have been designed in the experimental setup, which can collect intensity data in real time. Based on these data, we reconstruct the emission coefficient using the MLFRT. Then, a spectral line relative intensity method was chosen to calculate the 3-D temperature distribution, where the spectral analysis of argon arc plasma was introduced. This new technology can acquire good result by just two orthographic intensity data sets. Therefore, the experimental system is simple, and the experimental cost is low. The result is beneficial to understand the working principle of argon arc plasma, improving the level of craftsmanship. It also has good application advantages over other 3-D flow field testing, such as density field, pressure field, velocity field, etc. It shows great academic and economic value. [ABSTRACT FROM PUBLISHER]

In this paper, we present a probabilistic spatial approach to build compact 3-D representations of unknown objects probed by tactile sensors. Our approach exploits the high frame rates provided by modern tactile sensors and utilizes Kalman filters to build a probabilistic model of the contact point cloud that is efficiently stored in a kd-tree. The quality of generated shape representations is compared with a naive averaging approach, and we show that our method provides superior accuracy. We also evaluate the feasibility of object classification combining the generated object representations, together with the iterative closest point algorithm. [ABSTRACT FROM AUTHOR]

Web vibration phenomena that occur in winding! unwinding systems have a knock-on economical effect for the numerous firms that utilize this equipment. Among many sources of disturbances, out-of-plane and lateral displacements of a moving web are well known to be two main limiting factors of web transport velocity in the industry. To tackle this problem, we address, in this paper, a new approach for the detection and monitoring of the most significant web displacements encountered, which are the simultaneous edge web lateral displacements and out-of-plane web vibrations. This technique involves a fast vision system composed of two digital cameras (≥ 2 × 100 i/s) and a laser stripe lines pattern device. It is a contactless technique that allows catching out-of-plane web vibration properties during the winding process. Due to a well-known edge-tracking algorithm and fast but simple image segmentation algorithms in the field of binary machine vision, both edge web and out-of-plane vibration frequencies and magnitudes are estimated in real time. The latter are extracted from the analysis of the relative depth variations of the web surface with respect to the common camera frame. Experiments have been conducted on a winding plant for elastic fabric. Together with the 3-D displacements of the web edges, the two most significant frequencies of web vibrations have been estimated for a sequence of images and compared with those computed with a simple elastic string model in motion. [ABSTRACT FROM AUTHOR]

Three-dimensional reconstruction techniques are widely used to provide a spatial description of scoliotic spines. One example is the 3-D reconstruction method developed and routinely used at Sainte-Justine Hospital. It concerns the reconstruction of six anatomical landmarks per vertebra from the frontal and lateral radiographs: endplate centers; inferior and superior tips of both pedicles. Although this “standard” method is accurate, it requires 2 h for an expert technician to identify all anatomical landmarks on radiographs.Objective. – Therefore, this paper presents a novel and fast computed acquisition method providing a reconstruction of the spine better suited to the needs of the orthopedists during scoliosis clinics.Materials and Methods. – In this approach, five to eight points are identified on the frontal and lateral radiographs to obtain the overall shape of the spine. 2-D average predictive models, are built from a database of 791 radiographs, allowing to estimate the 2-D coordinates of the six vertebral landmarks and to obtain their 3-D coordinates from the DLT algorithm.Results and conclusions. – The evaluation of this “fast method” shows that the minimum number of points to be identified on the frontal radiograph is six for right thoracic or left lumbar curves and eight for right thoracic–left lumbar curves. Seven points need to be identified on the lateral radiograph. Furthermore, average models corresponding to a specific type and severity of scoliosis allow the 2-D mean differences between “standard” and “fast” methods to be less than 3.7 mm for endplate landmarks and 5.0 mm for pedicles. No significant difference was found between clinical indices obtained from both methods, confirming that the “fast” method is well adapted for direct clinical use. [Copyright &y& Elsevier]

• Applying iterative closest point algorithm to stitch point clouds. • Employing semi-global block matching algorithm for stereo correspondence problems. • Incorporating structural information of objects to improve point cloud registration accuracy. • Interpolating surfaces onto point clouds of construction material for volume estimation. Bucket fill factor is of paramount importance in measuring the productivity of earth-moving machines which is the amount of material loaded in the bucket within one scooping. In this paper, a stereo vision-based method is proposed and a novel perception system is developed. The system tested on a wheel loader is able to provide an accurate estimation of the fill factor. Disparity is computed for a pair of stereo images to reconstruct high fidelity 3-D point clouds. Preliminary processing is then used to extract regions of interest. In addition to applying existing state-of-the-art techniques including point cloud registration, stitching, and surface interpolation, our system also incorporates the structural information of wheel loaders, achieving excellent performance of 94.72 % accuracy even under the unavailability of visual information due to occlusion, and under different environment conditions. This research paves the way for the arrival of fully autonomous earth-moving machines in the future. [ABSTRACT FROM AUTHOR]

Evaluation of the environmental impact of gas plumes from stack emissions at the local level requires precise knowledge of the spatial development of the cloud, its evolution over time, and quantitative analysis of each gaseous component. With extensive developments, remote-sensing ground-based technologies are becoming increasingly relevant to such an application. The difficulty of determining the exact 3-D thickness of the gas plume in real time has meant that the various gas components are mainly expressed using correlation coefficients of gas occurrences and path concentration (ppm.m). This paper focuses on a synchronous and non-expensive multi-angled approach combining three high-resolution visible cameras (GoPro-Hero3) and a scanning infrared (IR) gas system (SIGIS, Bruker). Measurements are performed at a NH3 emissive industrial site (NOVACARB Society, Laneuveville-devant-Nancy, France). Visible data images were processed by a first geometrical reconstruction gOcad® protocol to build a 3-D envelope of the gas plume which allows estimation of the plume’s thickness corresponding to the 2-D infrared grid measurements. NH3 concentration data could thereby be expressed in ppm and have been interpolated using a second gOcad® interpolation algorithm allowing a precise volume visualization of the NH3 distribution in the flue gas steam. [ABSTRACT FROM AUTHOR]