Number Of Feature Points Research Articles

Rapid Labels: Point-Feature Labeling on GPU.

Labels, short textual annotations are an important component of data visualizations, illustrations, infographics, and geographical maps. In interactive applications, the labeling method responsible for positioning the labels should not take the resources from the application itself. In other words, the labeling method should provide the result as fast as possible. In this work, we propose a greedy point-feature labeling method running on GPU. In contrast to existing methods that position the labels sequentially, the proposed method positions several labels in parallel. Yet, we guarantee that the positioned labels will not overlap, nor will they overlap important visual features. When the proposed method is searching for the label position of a point-feature, the available label candidates are evaluated with respect to overlaps with important visual features, conflicts with label candidates of other point-features, and their ambiguity. The evaluation of each label candidate is done in constant time independently from the number of point-features, the number of important visual features, and the resolution of the created image. Our measurements indicate that the proposed method is able to position more labels than existing greedy methods that do not evaluate conflicts between the label candidates. At the same time, the proposed method achieves a significant increase in performance. The increase in performance is mainly due to the parallelization and the efficient evaluation of label candidates.

PLS-VINS: Visual Inertial State Estimator With Point-Line Features Fusion and Structural Constraints

One of the limitations of visual Simultaneous Localization and Mapping (VSLAM) of point-based is that it relies too much on scene features. When the texture information in the scene is missing or the image is blurred due to the rapid movement of the camera, the number of point features is often small, which affects the accuracy of pose estimation. Line feature information contains more geometric elements than point feature information. We propose a visual-inertial state estimator system based on point-line features and structure constraints (PLS-VINS), which combines both of points and line segments to enhance the performance of feature extraction in a wider variety of scenarios and optimizes the system states by jointly minimizing the pre-integration constraints of inertial measurement unit (IMU). Particularly in those where point features are scarce or not well-distributed in the image, PLS-VINS can extract many line features from artificial objects, which can provide more structural constraints (collinear, vertical, and parallel) for visual navigation, such as vertical and parallel constraints. Compared with the classic SLAM methods which use point-line fusion algorithm, we have adopted a new line feature error reprojection model and added structural constraints of man-made buildings in the back-end optimization to improve the robustness and accuracy in an illumination-changing environment. The proposed PLS-VINS has been extensively tested in both synthetic and real-world experiments whose results demonstrate that the proposed system outperforms the state-of-the-art methods in various scenarios. Compared with the VINS-Mono, the positioning RMSE in this study increases by 29.46% and 23.79% in rotation and translation for Dataset 1–1 with EuRoc Dataset, and by 55.64% in translation for Dataset 2–1 of actual scene with weak texture environment, respectively.

Study of the quality construction of photogrammetric models obtained in low-light conditions

Relevance of the research topic. The paper shows main results of environmental parameters that affect the quality of 3D-models obtained by the photogrammetric method of surveying. Research objective. The article presents: the fundamental possibility of using a small-sized photogrammetric device for underground surveying and the parameters that affect the result of shooting in a confined low-light space. Research methods. Experiments included a set of independent serial photographs of a test site. To increase the results of experiments, object with a simple geometric shape have been used as test objects for extrapolating of the results of the survey to products of standard metal products. In these conditions, imitating abstract underground mine workings: with the lack of lighting, confined spaces, a small number of characteristic points in the background. The texture of the subject of photogrammetric survey and common geometric parameters of photo base accepted as studied factors. Various images were projected onto the test scene to form an artificial texture. Results and its applications. The experimental results confirm the possibility of using the proposed methods for identifying engineering communications nodes, oil and gas production facilities, elements of lifting machines and conductors in vertical mining devices. In addition, the authors performed an idea of improving the quality of photogrammetric models by projecting temporary artificial textures on the subject. The results of the work can be used for the improving of the methods of surveying, using digital photogrammetry technology Findings. It is possible to imrove the quality of digital photogrammetric models of engineering structures by projecting artificial textures onto them. The possibility of the creation of models of the subject increases the accuracy and controllability of the result. With increasing contrast and complexity of the texture being applied, digital photogrammetry algorithms better determine the correspondence between a pair of photographs.

Study on flow characteristics of dilute phase flexible ribbon particles in a fluidised bed riser using particle tracking velocimetry

Flexible ribbon particles tend to rotate, deform (bend) and intertwine with each other in a fluidised bed due to their high flexibility and filamentous shapes. The movements of these particles have a significant influence on the formation of the so-called clusters, which lead to the complex hydrodynamic characteristic and subsequently poor equipment performance. However, there is currently no method for accurately defining and effectively measuring these complex particle movements, especially for their non-translational movements. In this paper, the flow characteristics of these particular flexible ribbon particles in a cold fluidised riser are studied using an improved particle tracking velocimetry (PTV) method. A certain number of characteristic points are selected in the longitudinal direction of a single flexible ribbon particle. The translation and non-translation movements of the characteristic points are defined and measured, and then the motion characteristics of the flexible ribbon particles are obtained. This work aims to provide an insight into this particular type of particle flow and to benefit the design and scale-up of related equipment. It is found that particles are most likely to collide, rotate and deform in the neighbouring wall regions with small superficial gas velocity. However, excessive particle contacts inhibit their free movements. By using regression analysis, an empirical correlation is established among the fractions of particles undergoing movement (both translational and non-translational), mass flow ratio (solid to gas) and particle Reynolds number.

Prediction-Based Object Tracking in Visual Sensor Networks

This paper is to investigate the mobile object tracking in visual sensor networks. When visual sensors equipped with cameras are randomly deployed in a monitoring environment, many sensors are involved in covering the same mobile object. In a visual sensor network, images of the object may be captured by different sensors in different orientations simultaneously, and the captured images are then sent back to a base station or server. However, achieving full coverage for a set of selected characteristic points of an object invariably involves a great deal of redundant image data consuming the transmission energy for a visual sensor network. A novel approach is proposed to overcome this problem. The minimal number of sensors required for set coverage can be determined by predicting the direction and speed of the mobile object. Such sets are capable of covering the maximal number of characteristic points of view related to the mobile object at one time. The simulation results show that this approach reduces transmission cost while preserving the maximal coverage range of mobile objects.

A method for inversion of periodic open boundary conditions in two-dimensional tidal models

For parameter estimation problems, it is of great importance to reduce the number of spatially varying control variables because of the ill-posedness of inverse problem. A new method for the inversion of periodic open boundary conditions in two-dimensional tidal models is developed in this work. In this method, the open boundary curves are generated by linearly interpolating the values at feature points (FPs). The FPs are selected by calculating the second-order derivatives of discrete curves. The advantage is that most of the variations of the curves can be reproduced by the minimum number of control points. The adjoint-based 4DVAR data assimilation method is then applied to simulate the tides in the Bohai, Yellow and East China Seas by optimizing the Fourier coefficients at FPs. The model and the method are calibrated in twin experiments where the prescribed distributions along open boundaries are successfully inverted. The results of twin experiments demonstrate that the effect of inversion is in inverse proportion with the number of FPs which characterizes the complexity of open boundary curves. In order to test the method in practical application, real experiments are performed and the FPs are selected by analyzing the background information from a global tidal model DTU10. During the assimilation, both the data misfit between observations and modeling results and L2 norm of gradients of cost function with respect to control variables have decreased significantly. The relation between the number of control variables and parameter inversion is discussed. It is concluded the method developed in this work will be especially useful and effective when dealing with complex open boundary forcing or applying in highly refined models.

Closed-Form Solution of Visual-Inertial Structure from Motion

This paper investigates the visual-inertial structure from motion problem. A simple closed form solution to this problem is introduced. Special attention is devoted to identify the conditions under which the problem has a finite number of solutions. Specifically, it is shown that the problem can have a unique solution, two distinct solutions and infinite solutions depending on the trajectory, on the number of point-features and on their layout and on the number of camera images. The investigation is also performed in the case when the inertial data are biased, showing that, in this latter case, more images and more restrictive conditions on the trajectory are required for the problem resolvability.

A novel videomicroscopic technique for studying rat ureteral peristalsis in vivo

Existing techniques do not allow analyzing the fine movements of the ureteral wall during in vivo peristaltic contractions. A videomicroscopic technique has been developed to study the active mechanical displacements of the rat ureter. The middle portion of the ureter in a length of 16-18 mm was elevated from its base by microsurgical preparation, encased in a specific tissue chamber and continuously superfused with physiological saline. Contractions were recorded by videomicroscopy. A number of characteristic points on the surface were identified by the pattern of vasa vasorum. Their movements were analyzed in a coordinate system defined by the axial and radial directions of the segment. Identified surface points on the ureter moved along characteristic trajectory loops during contractile cycles. In addition to the synchronized longitudinal and circumferential contractions, typical axial displacement cycles could be identified. Our observations demonstrate that longitudinal contractions might be more important in transporting the urine as thought earlier because of the axial tether of the ureter. (1) A longitudinal contraction ring preceding the circumferential one axially distends the distal segments. (2) Initial phase of the longitudinal contraction ring promotes bolus volume rearrangement toward the passive diameter dilation. (3) Longitudinal contraction with the maximum circumferential contraction ring just behind it helps pushing the urine bolus downward. (4) Ureteral segments proximal to the longitudinal contraction ring will be passively axially stretched which also helps their filling.

Generalization of Contours Using Deviation Angles and Error Bands

In this paper a new approach for generalization of contours is described. The aim of this approach is to obtain both simplified and smoothed contours lying on a minimum number of characteristic points and inside the error bands. Characteristic points of contours are defined in relation to the skeleton lines of the terrain and determined using the deviation angles at the contour points. Error bands for contours are constructed by means of the steepest slope lines and the mean square planimetric errors at the contour points. The new approach is compared to the Li-Openshaw algorithm according to the experimental testing results.

Facial animation by reverse morphing on a sequence of real images: application to film and video production

Research on facial animation is as vast as the many interests and needs that can be found in the general public, television or film production. For Mac Guff Ligne, a company specialized in the fabrication of special effects and computer generated images, the needs and the constraints on such a topic are very big. Morphing is often used in facial animation, and consists in mixing several expression models. As we will discover, the advantages in using morphing are numerous, but the animation workload remains long and time-consuming. Our goal is to propose a fast and reliable animation tool that is based on the same morphing technique with which the graphic artists are familiar. Our method is to inverse the classical process of morphing, and to match a real facial animation to a 3D facial animation by automatic calculation of the weights of expression models. Firstly, we discretize the real facial animation using a number of characteristic points. Then we follow the path of each point by optic or magnetic motion capture, or through the filmed images. This tracked down animation is then decomposed, for each frame, according to a basis of characteristic expressions (joy, anger, etc.) that can be automatically taken out from the real animation during the calibration stage. It means that we express a simplified shape of the face by linear composition of a series of basic faces. Finally, we can reintroduce the results of this decomposition into a more complex facial morph which has a totally different topology and geometry. The user can thus complete and modify the resulting animation using a tool he knows well. This method, used in production at Mac Guff Ligne, proves to be a solid, effective and easy-to-use work base for facial animation.

Knowledge-based landmarking of cephalograms

Orthodontists have defined a certain number of characteristic points, or landmarks, on X-ray images of the human skull which are used to study growth or as a diagnostic aid. This work presents the first step toward an automatic extraction of these points. They are defined with respect to particular lines which are retrieved first. The original image is preprocessed with a prefiltering operator (median filter) followed by an edge detector (Mero-Vassy operator). A knowledge-based line-following algorithm is subsequently applied, involving a production system with organized sets of rules and a simple interpreter. The a priori knowledge implemented in the algorithm must take into account the fact that the lines represent biological shapes and can vary considerably from one patient to the next. The performance of the algorithm is judged with the help of objective quality criteria. Determination of the exact shapes of the lines allows the computation of the positions of the landmarks.

Point-contact noise spectroscopy of phonons in metals

The spectral density of low-frequency electrical fluctuations (noise) in pure metal point contacts is found to depend nonmonotonically on the potential difference at low temperatures. For contacts satisfying the conditions for the ballistic regime of electron current flow the noise is made up of a monotonic part proportional to the square of the dc voltage (1/f noise) and a “spectral part” with extrema at biases corresponding to the characteristic phonon energies. Comparison of the noise spectrum part for sodium with the calculated contribution introduced by Umklapp processes in the point-contact electron-phonon interaction function shows that these characteristics are similar. Analysis of noise spectra and dispersion curves of phonons in the main crystallographic directions for three metals (sodium, copper, and tin) makes it possible to establish that the positions of maxima in the noise spectra correspond to the energies at which Umklapp processes are allowed. At the same time the positions of minima correlate well with the energies of phonons possessing maximum wave vectors and minimum group velocities. The latter regularity is attributed to stimulated emission of coherent phonons due to normal processes. This emission reduces the noise due to the correlation between separate electron-phonon scattering events. Thus, the spectral density of low-frequency fluctuations as a function of dc potential difference (the “noise spectrum”) is found to contain more detailed information about phonons, enabling one to determine their energies at a number of characteristic points on the dispersion curves.

Studies of the mechanism of formation of calcium silicate compounds by titration based on emission and atomic absorption spectroscopy

In this paper, the inhibition effect of silicate on emission or absorption of calcium was used for an investigation of the mechanism of formation of calcium silicate compounds. For that purpose, calcium chloride solutions were continuously titrated with a standard solution of sodium silicate (Na 2SiO 3), with simultaneous aspiration of the titrand into an air-hydrogen flame. During the titration, changes in the emission of the CaO-band at 622 nm and the CaOH-band at 554 nm were registered automatically on the recorder. Changes in the absorption of calcium were also registered at 422 nm. Thus curves of the same shape were obtained, with the same number of characteristic points, in which the SiO 2/Ca ratio is constant, when the concentration of silicate in the titrant varies. This fact suggests that calcium reacts with silicate to form compounds with a constant composition. Curves of the same shape were obtained by titration of a standard solution of sodium silicate, with a calcium chloride solution, while monitoring the changes in the absorption of calcium at 422 nm and changes in the emission of the CaO-band at 622 nm. In this case, the mole ratios SiO 2/Ca at the characteristic points of the curves were the same as in the case of the titration of calcium chloride solution with the silicate solution. On the basis of the mole ratios SiO 2/Ca at the characteristic points on the titration curves, which amount to 0.21, 0.33 and 0.50, the mechanism of formation of calcium silicate compounds was represented by chemical equations. It may be concluded that in the process of evaporation of spray droplets a chain of reactions take place, resulting in compounds that can be represented by the general formula xCaO·SiO 2.