Displacements Of Feature Points Research Articles

An experimental study of a novel external fixator based on universal joints for the rapid initial stabilization of mandibular comminuted fractures

PurposeShaping and assembling contemporary external fixators rapidly for the severe mandibular fractures remains a challenge, especially in emergency circumstance. We designed a novel external fixator that incorporates universal joints to provide the stabilization for mandibular comminuted fractures. This study aims to confirm the efficacy of this novel external fixator through biomechanical tests in vitro and animal experiments. MethodsIn vitro biomechanical tests were conducted using 6 fresh canine with mandibular defect to simulate critical comminuted fractures. Three mandibles were stabilized by the novel external fixator and other mandibles were fixed by 2.5 mm reconstruction plates. All fixed mandibles were subjected to loads of 350 N on the anterior regions of teeth and 550 N on the first molar of the unaffected side. The stability was evaluated based on the maximum displacement and the slope of the load-displacement curve. In animal experiments, 9 beagles with comminuted mandibular fractures were divided into 3 groups, which were treated with the novel external fixation, reconstruction plate, and dental arch bar, respectively. The general observation, the changes in animals’ weight, and the surgical duration were recorded and compared among 3 groups. The CT scans were performed at various intervals of 0 day (immediately after the surgery), 3 days, 7 days, 14 days, 21 days, and 28 days to analyze the displacement of feature points on the canine mandible and situation of fracture healing at 28 days. The statistical significance was assessed by the two-way analysis of variance test followed by the Bonferroni test, enabling multiple comparisons for all tests using GraphPad Prism10.1.0 (GraphPad Inc, USA). ResultsThe outcomes of the biomechanical tests indicated that no statistically significant differences were found in terms of the maximum displacement (p = 0.496, 0.079) and the slope of load displacement curves (p = 0.374, 0.349) under 2 load modes between the external and internal fixation groups. The animal experiment data showed that there were minor displacements of feature points between the external and internal fixation groups without statistic difference, while the arch bar group demonstrated inferior stability. The CT analysis revealed that the best fracture healing happened in the internal fixation group, followed by the external fixation and arch baring at 28 days after fixation. The external fixation group had the shortest fixation duration (25.67 ± 3.79) min compared to internal fixation ((70.67 ± 4.51) min, p < 0.001) and arch baring ((42.00 ± 3.00) min, p = 0.046). ConclusionThe conclusion of this study highlighted the efficacy and reliability of this novel external fixator in managing mandibular fractures rapidly, offering a viable option for the initial stabilization of comminuted mandibular fractures in the setting of emergency rescue.

Research on Full-Field Dynamic Deflection Measurement of Beams Based on Dense Feature Matching and Mismatch Removal Method

To solve the problems of measurement errors led by mismatches of dense feature matching in machine vision structural deflection measurement, this paper proposes a dense feature extraction, matching, and dual-step mismatch-removal-based full-field structural dynamic deflection measurement method. First, the of dense feature detection and matching theory is introduced to extract the SIFT feature points on a structural surface in an image sequence and matched by FLANN to trace the structure movement, and the mechanisms and causes of mismatches are analyzed. Then, a dual-step mismatch removal method combining RANSAC and Structural Displacement Continuity Restriction (SDCR) is introduced to achieve full-field dynamic beam deflection measurement. The proposed method is validated through indoor cantilever beam experiments, and results show that the method can effectively eliminate a large number of SIFT feature mismatches (accounting for approximately 55% of the total matched feature points). The full-field dynamic displacement field of the beam can be measured with the correctly matched dense feature points by converting dense feature point displacements into continuous and uniform spatiotemporal deflections of the structure. A comparison with the GOM Correlate Professional DIC measurement system was conducted, and the maximum measurement error of the cantilever beam dynamic displacement of the proposed method is between 0.024 and 0.053 mm, the root mean squared error of displacement is approximately 0.01 mm, and the correlation coefficient between two deflection–time curves reaches 0.9964. The proposed algorithm is proven to be effective in full-field displacement measurement and has great potential in future structural health monitoring of bridges.

Real-time Sequence Images Registration based on Fast Least Squares Feature Point Tracking

This study addresses the issues of diminished precision and sluggish computational pace observed in current sequence image registration algorithms. A sequence image registration algorithm based on adaptive feature point selection (AFPS) and fast least squares tracking (FLST) is proposed. The corner points are detected by the FAST algorithm. The feature points are selected according to the distribution and intensity of the corner points. The fast least squares tracking technique is employed to compute the displacement of feature points between successive images. The proposed feature point selecting approach and the tracking method substantially increased the efficiency and performance of the registration algorithm. The registration algorithm is evaluated by sequence images taken by drones. The test outcomes demonstrate that, in comparison to existing algorithms, the proposed algorithm significantly enhances both the accuracy and real-time capabilities of sequence image registration.

Accuracy and sensibility analysis of strain measurement based on microimages captured by smartphone with a microscope

Strain measurement is an essential part of structural health monitoring (SHM). The objective of the study is to propose a new method to measure strain on the surface of a structure. The speeded-up robust feature (SURF) method was applied to detect and trace feature points in microimages that were obtained using a smartphone with a compact microscope. Subsequently, the average displacement of feature points in microimages was calculated before and after deformation. Finally, the average strain of a certain distance in the structure surface was obtained. An experiment was performed to measure the average strain in an optical fiber of certain length and compare the data with that measured by the fiber Bragg granting (FBG) to verify the accuracy of the proposed method. Additionally, a water drop loading experiment was performed on the optical fiber to test the sensitivity of the proposed method. The results indicated that the strain measured by the smartphone with a compact microscope was in agreement with the FBG data. The error analysis illustrates the maximum error of the data measured by the two methods is 6με, and this can satisfy the requirements of civil engineering. The result of the water drop experiment reveals that the entire process of loading via water drops can be measured by the proposed method, and strain increases with the drops of water. The experimental results verify that the feasibility of the proposed method can satisfy the needs of structural health monitoring for general buildings.

Strain Measurement Based on Speeded-up Robust Feature Algorithm Applied to Microimages from a Smartphone-Based Microscope.

The objective of this study is to evaluate and improve the accuracy and stability of a strain measurement method that uses the speeded-up robust feature (SURF) method to trace the displacement of feature points in microimages and obtain the strain in objects. The microimages were acquired using a smartphone with a portable microscope, which has a broad prospect of application. An experiment was performed using an unpacked optical fiber as the experimental carrier. The matching effect of the SURF method was analyzed in the microimage, and the M-estimator sample consensus (MSAC) algorithm was used to reject outliers generated by SURF. The results indicated that the accuracy of strain measurement using the proposed method is improved by modifying the feature point tracking method and measurement method. When compared with the fiber Bragg grating (FBG) data, the maximum standard error corresponded to 2.5 με, which satisfies the requirement of structural health monitoring (SHM) in practical engineering.

RAPID: Measuring Deformation of Biological Tissues from MR Images Through the Riemannian Pseudo Kernel

Due to the nonlinear deformation of nonrigid and nonuniform tissues, it is challenging to accurately measure the displacements of feature points distributed on the inner parts, boundaries, and separatrices of tissue layers. To address this challenge, we propose a feature point matching technique called RAPID to measure MR 2D slice deformation of nonuniform and nonrigid biological tissues. We propose to use the covariance of several neighboring point statistics computed around a keypoint, as the keypoint descriptor. Inspired by the kernel methods, we advocate adopting a Riemannian pseudo kernel to map SPD matrices to a high dimensional Hilbert space, where the Euclidean geometry applies. We compare our RAPID with two existing schemes (i.e., SIFT and SURF). Our experimental results show that our RAPID is superior to SIFT and SURF, because the benefits offered by RAPID are two-fold. First, our RAPID increases the number of matched data points. Second, RAPID substantially improves the key-point matching accuracy of SIFT and SURF.

Full-field Measurement of Deformation and Vibration using Digital Image Correlation

The main intention of this study was to investigate the full-field measurement of de-formation and vibration using a program we developed for digital image correlation. Digital image correlation is a measuring method that can calculate the displacement of each point on an object by using recorded images. By capturing continuous images of the object in deformation or in motion, the displacements of feature points on the object can be tracked and used in calculations to determine the full-field deformation, strain and vibration of the object. We used the fast and simple algorithm in our program as the core, and conducted non-contact full-field displacement measurement by tracking feature points from images taken after motion. The measuring accuracy can be up to 0.1 pixel. Our experimental results show the technique to be very accurate and useful. We also applied this technique under conditions where an ordinary sensor could not be used.

Orientation estimation in modern wearables with visual feature tracking

In this paper we propose and examine a robust method for orientation estimation of wearables (like Google Glass) through bias compensation of gyroscope. Through integration of raw angular rates, the resulting orientation estimate will drift, due to the non-zero bias of the measured gyroscope was also accumulated. A simple error model was constructed for the measurement capabilities of the device, in terms of inertial sensing of rotation. Using the benefits of feature point displacements (as optical flow) from the camera of the device, a sensor fusion algorithm was developed to lower, and compensate the bias. The introduced orientation estimator and bias removal method is based on adaptive reliability filter for the optical flow feature points. To fuse the remaining feature point displacements into one single value, various aggregation methods have been tested, and a maximum a-posteriori estimator was applied on the dataset. To further lower the bias from the gyroscope, the output of the system was used as a feedback to calculate a bias estimate. To measure the performance and investigate the benefits of the asynchronous work-flow, the optical flow was performed on various devices in real time. To validate the results of the simulations, real world measurements were performed with industrial robots. Our reliable, adaptive filter matched our expectations, could compensate the bias well, and the integrated output of the system had no significant drift.

Full-field Measurement of Deformation and Vibration using Digital Image Correlation

The main intention of this study was to investigate the full-field measurement of de-formation and vibration using a program we developed for digital image correlation. Digital image correlation is a measuring method that can calculate the displacement of each point on an object by using recorded images. By capturing continuous images of the object in deformation or in motion, the displacements of feature points on the object can be tracked and used in calculations to determine the full-field deformation, strain and vibration of the object. We used the fast and simple algorithm in our program as the core, and conducted non-contact full-field displacement measurement by tracking feature points from images taken after motion. The measuring accuracy can be up to 0.1 pixel. Our experimental results show the technique to be very accurate and useful. We also applied this technique under conditions where an ordinary sensor could not be used.

The Elastoplastic Finite Element Analysis for the Deep Anti-Sliding Stability of Gravity Dam by the Method of Overloading

Combined with engineering requirements of the Qingyu reservoir, the ANSYS finite element software was used to establish an elastoplastic gravity dam calculation model which considered the mechanical properties of weak structural plane of rock in the dam foundation. An analysis based on not only the finite element iteration not converging,the plastic zones in dam foundation rock developing to through the foundation and the mutation in horizontal displacement of feature points, but also the discontinuous variation of the distribution of horizontal displacement of dam foundation rock, the dislocation between the above and below of weak layers and the leap of iterations were took as the criterions to get the deep anti-sliding stability safety factor of gravity dam by gradually increasing the load burdened on the upstream face of the dam. This thesis illustrated the principle of the elastoplastic finite element analysis for the deep stability of gravity dam by the method of overloading, demonstrated the feasibility of this method ,expanded the criterions to determine the safety factor and obtains the safety factor of this practical engineering under the elastoplastic overloading method.

Facial expression recognition based on anatomy

In this study, we propose a novel approach to facial expression recognition that capitalizes on the anatomical structure of the human face. We model human face with a high-polygon wireframe model that embeds all major muscles. Influence regions of facial muscles are estimated through a semi-automatic customization process. These regions are projected to the image plane to determine feature points. Relative displacement of each feature point between two image frames is treated as an evidence of muscular activity. Feature point displacements are projected back to the 3D space to estimate the new coordinates of the wireframe vertices. Muscular activities that would produce the estimated deformation are solved through a least squares algorithm. We demonstrate the representative power of muscle force based features on three classifiers; NB, SVM and Adaboost. Ability to extract muscle forces that compose a facial expression will enable detection of subtle expressions, replicating an expression on animated characters and exploration of psychologically unknown mechanisms of facial expressions.

Study on the Development of Slope's Plastic Zone by Strength Reduction FEM

Based on the idea presented in literature [4]:when to calculate the safety coefficient by strength reduction FEM, The material's shear strength parameters c and φ will be deducted,it is suggested that sinφ≥ 1-2v.This paper study on the development of slope's plastic zone with different v and by strength reduction FEM, research show that the effect of v on the safety coefficient is not obvious,but when φ=20 and v beside critical value,the effect to the development of the plastic zone is obvious. When the value is bigger, the development of plastic zone occurs in the deep and the potential sliding channel cannot feed through.According this ,this paper puts forward a comprehensive evaluation method that combined with three instability criterions that finite element calculation does not converge,plastic zone run through,displacement of feature points appear inflection point.

Research on Velocity-Displacement Curve for Mechanical Linkage Servo Press

With main transmission system structural form of main servo motor-worm and worm gear commutation reducer-transmission screw-linkage force increasing mechanism, mathematical model of linkage force increasing mechanism is established to obtain the relationships of the velocity and displacement between nut and slide. Velocity and displacement of feature points of slide on the velocity-displacement curve inputted by user transform into which of nut by binary search algorithm and linear interpolation calculation. The feature points of nut transform into the velocity and displacement arrays of points based on S-curve, and then the arrays of points transfer through UDP protocol to lower computer. After the linear fine interpolation by Siemens Simotion D425 motion controller, slide moves according to the setting velocity-displacement curve. The experimental results show that slide moves smoothly, which meets specific technology requirements. The achievements have been successfully applied to a self-developed 2000KN mechanical linkage servo press in a production line of hot forming technology for more than one year, which extends the technology application scope of traditional mechanical press, and improves product quality.

An Efficient Approach for Dynamic Calibration of Multiple Cameras

In this paper, we propose a new algorithm for dynamic calibration of multiple cameras. Based on the mapping between a horizontal plane in the 3-D space and the 2-D image plane on a panned and tilted camera, we utilize the displacement of feature points and the epipolar-plane constraint among multiple cameras to infer the changes of pan and tilt angles for each camera. This algorithm does not require a complicated correspondence of feature points. It can be applied to surveillance systems with wide-range coverage. It also allows the presence of moving objects in the captured scenes while performing dynamic calibration. The sensitivity analysis of our algorithm with respect to measurement errors and fluctuations in previous estimations is also discussed. The efficiency and feasibility of this approach has been demonstrated in some experiments over real scenery.

A vision-based technique for objective assessment of burn scars.

In this paper a method for the objective assessment of burn scars is proposed. The quantitative measures developed in this research provide an objective way to calculate elastic properties of burn scars relative to the surrounding areas. The approach combines range data and the mechanics and motion dynamics of human tissues. Active contours are employed to locate regions of interest and to find displacements of feature points using automatically established correspondences. Changes in strain distribution over time are evaluated. Given images at two time instances and their corresponding features, the finite element method is used to synthesize strain distributions of the underlying tissues. This results in a physically based framework for motion and strain analysis. Relative elasticity of the burn scar is then recovered using iterative descent search for the best nonlinear finite element model that approximates stretching behavior of the region containing the burn scar. The results from the skin elasticity experiments illustrate the ability to objectively detect differences in elasticity between normal and abnormal tissue. These estimated differences in elasticity are correlated against the subjective judgments of physicians that are presently the practice.

Visual information for categorizing facial expression of emotions

AbstractTwo experiments were conducted to reveal the visual information from the face utilized for the categorization of its expression of emotions. In Experiment 1 the subjects produced six schematic faces expressing six basic emotions by using a computer graphics system. By a series of factor analyses on the variables of displacements of feature points for deforming a neutral schematic face to produce the six expressional ones, two factors of ‘curvedness/openness’ and ‘slantedness’ of facial elements were obtained. In Experiment 2 another group of subjects made category judgements of emotions for 72 of the total 216 schematic faces produced in Experiment 1. The relationship between the displacements of feature points in Experiment 1 and subjects' categorical responses in Experiment 2 were examined by canonical discriminant analysis. It was found that the categorical judgements were well explained by two canonical variables whose structures were quite similar to those of factors obtained in Experiment 1. These results indicated that we extract the information of changes in curvedness/openness and slantedness of facial elements among other information on the face for categorizing its expressions of emotions. Lastly, the relationship between the dimensions of visual information obtained here and those of semantic affective meanings found in earlier research was discussed.