Guangwen Jiang

Fold-ray videometrics method for the deformation measurement of nonintervisible large structures.

An optical measurement method, the fold-ray videometrics method, that is applicable to the deformation measurement of large structures is proposed. Through an illustration of ship deformation, the principle of fold-ray videometrics and the composition of the deformation measurement system are introduced. The fold-ray videometrics method is able to transfer or relay three-dimensional geometric information with a fold-ray optical path and thus is capable of real-time measurement of three-dimensional positions, attitudes, and deformations between nonintervisible objects and those of intervisible objects with a very large angle of view. The proposed method therefore has the potential to be applied in deformation measurement of large structures.

Attitude-correlated frames approach for a star sensor to improve attitude accuracy under highly dynamic conditions

The attitude accuracy of a star sensor decreases rapidly when star images become motion-blurred under dynamic conditions. Existing techniques concentrate on a single frame of star images to solve this problem and improvements are obtained to a certain extent. An attitude-correlated frames (ACF) approach, which concentrates on the features of the attitude transforms of the adjacent star image frames, is proposed to improve upon the existing techniques. The attitude transforms between different star image frames are measured by the strap-down gyro unit precisely. With the ACF method, a much larger star image frame is obtained through the combination of adjacent frames. As a result, the degradation of attitude accuracy caused by motion-blurring are compensated for. The improvement of the attitude accuracy is approximately proportional to the square root of the number of correlated star image frames. Simulations and experimental results indicate that the ACF approach is effective in removing random noises and improving the attitude determination accuracy of the star sensor under highly dynamic conditions.

Study of a pose-relay videometric method using a parallel camera series

This study proposes a pose-relay videometric method that uses a parallel camera series and is applicable to measuring deformation between nonintervisible and intervisible objects with a very wide angle of view. The measuring system is constructed by adding symmetrical cameras to the pose-relay stations of a single camera measuring system to improve its robustness and precision. An adjustment data fusion method is suggested to take full advantage of the data redundancy among neighboring relay stations in the proposed system. Simulated results show that the adjusted method enhances the measuring precision achieved with the classic weighted average data fusion method owing to its use of the restraint condition inherent in the system.

The effects of temperature variation on videometric measurement and a compensation method

When a videometric system operates over a long period, temperature variations in the camera and its environment will affect the measurement results, which cannot be ignored. How to eliminate or compensate for the effects of such variations in temperature is an emergent problem. Starting with the image drift phenomenon, this paper presents an image-drift model that analyzes the relationship between variations in the camera parameters and drift in the coordinates of the image. A simplified model is then introduced by analyzing the coupling relationships among the variations in the camera parameters. Furthermore, a model of the relationship between the camera parameters and temperature variations is established with the system identification method. Finally, several compensation experiments on image drift are carried out, using the parameter-temperature relationship model calibrated with one arbitrary data set to compensate the others. The analyses and experiments demonstrate the feasibility and efficiency of the proposed method. This paper proposed a compensation method for eliminating the effects of temperature variation in the long duration application of image vision.A model of the relationship between the camera parameters and temperature variations is established with the system identification method.Experiments are carried on. The analyses and experiments demonstrate the feasibility and efficiency of the proposed method.

Region-confined restoration method for motion-blurred star image of the star sensor under dynamic conditions.

Under dynamic conditions, the centroiding accuracy of the motion-blurred star image decreases and the number of identified stars reduces, which leads to the degradation of the attitude accuracy of the star sensor. To improve the attitude accuracy, a region-confined restoration method, which concentrates on the noise removal and signal to noise ratio (SNR) improvement of the motion-blurred star images, is proposed for the star sensor under dynamic conditions. A multi-seed-region growing technique with the kinematic recursive model for star image motion is given to find the star image regions and to remove the noise. Subsequently, a restoration strategy is employed in the extracted regions, taking the time consumption and SNR improvement into consideration simultaneously. Simulation results indicate that the region-confined restoration method is effective in removing noise and improving the centroiding accuracy. The identification rate and the average number of identified stars in the experiments verify the advantages of the region-confined restoration method.

Two-step camera calibration method based on the SPGD algorithm.

Given the rapid convergence characteristic of the stochastic parallel gradient descent (SPGD) algorithm, this study proposes a method that applies the algorithm to a two-step camera calibration method to resolve the frequent iteration and long calibration time deficiencies that exist under the traditional two-step camera calibration method, thereby achieving rapid calibration. The method first uses image coordinates obtained with subpixel positioning technology as initial values of control variables, in addition to positive disturbances produced on a two-dimensional plane, then uses two-step theory to calculate the average value of aberrations. Based on the same rationale, negative disturbances are then produced and the average value of the aberrations is calculated. Finally if, after assessing whether to continue with further iterations based on the difference in these values, continued iterations confirm new control variables based on the SPGD algorithm iteration formula, a new cycle is started until the results satisfy requirements. Theoretical analysis and experimental results show that the proposed rapid calibration method using the SPGD algorithm in the two-step camera calibration method is 3-4 times faster than the traditional two-step calibration method, and that it has significant potential value for use in certain time-constrained projects.

Centroid error compensation method for a star tracker under complex dynamic conditions

The traditional approach of a star tracker for reducing the dynamic error concentrates on a single frame of star images. Through correlating adjacent star images together with their angular relations sensed by a gyroscope unit (GU), the attitude-correlated frames (ACF) approach expands the view from one single frame to frame sequences. However, the star centroid is shifted from the star true position at the center time of the exposure period under complex dynamic conditions, which is called the complex motion induced error (CMIE) in this paper. The CMIE has a large effect on the performance of the ACF approach. This paper presents a method to compensate the CMIE through reconstructing the star trajectory with the angular velocity of the star tracker sensed by a GU, which achieves effective compensation of the CMIE crossing the boresight direction. Since the observation sensitivity to the CMIE along the boresight direction is low, the attitudes from two different fields of view (FOVs) are combined to improve its compensation accuracy. Then the ACF approach is applied to the obtained results where the CMIE has already been compensated completely. Simulations under shipboard dynamic conditions and experiments under oscillating conditions indicate that the proposed method is effective in improving the performance of the ACF approach and reducing the dynamic error of a star tracker under complex dynamic conditions.

An Innovative Multi-headed Camera Network: A Displacement-Relay Videometrics Method in Unstable Areas

The subsidence of ground beds occurs frequently in large construction projects such as bridges, dams, high buildings and railways, which may cause damage and sometimes create disasters. Especially along with the establishment and the development of the high-speed railway, tiny subsidence and deformation of the railway beds will result in the decline in the service quality and safety. Therefore, automatic and long-duration subsidence surveillance is becoming increasingly important.

Study on design of infrared cooperative marker and extraction method of random irregular cross

The design of cooperative marker and the accuracy of target extraction are of great significance for precision of monocular pose measurement. To suit all-weather conditions in some applications, infrared cooperative marker combined by several crosses is designed, and each of the crosses is composed of a certain mount of infrared LEDs (Light Emitting Diodes) with the wavelength of 850 nanometers. When shooting at different directions, the angles between both arms of the cross and horizontal axis of the image are different and irregular. Aiming at detection of random and irregular cross, a new sub-pixel detection method based on GPI (gray projecting integration) and correlation is put forward. Experiments show that the proposed detection method is robust and can locate cross center with the accuracy prior to 0.05 pixels.

Analysis of a novel device-level SINS/ACFSS deeply integrated navigation method

The combination of the strap-down inertial navigation system(SINS) and the celestial navigation system(CNS) is one of the popular measures to constitute the integrated navigation system. A star sensor(SS) is used as a precise attitude determination device in CNS. To solve the problem that the star image obtained by SS is motion-blurred under dynamic conditions, the attitude-correlated frames(ACF) approach is presented and the star sensor which works based on ACF approach is named ACFSS. Depending on the ACF approach, a novel device-level SINS/ACFSS deeply integrated navigation method is proposed in this paper. Feedback to the ACF process from the error of the gyro is one of the typical characters of the SINS/CNS deeply integrated navigation method. Herein, simulation results have verified its validity and efficiency in improving the accuracy of gyro and it can be proved that this method is feasible.