Image Coordinates Of Feature Points Research Articles

A structured light vision sensor for on-line weld bead measurement and weld quality inspection

Weld bead measurement and weld quality inspection are important parts in industrial welding. In this paper, a structured light vision sensor is developed to achieve on-line weld bead measurement and weld quality inspection. Firstly, a structured light vision sensor with a narrow-band optical filter is developed to reduce welding noises such as arc lights and splashes. Secondly, the weld bead type identification algorithm including image pre-processing, baseline extraction, and weld bead classification is proposed to classify filling weld bead and capping weld bead. Thirdly, feature extraction algorithms of filling weld bead and capping weld bead are presented to obtain corresponding feature points. Combining the image coordinates of feature points with structured light vision model, the weld bead size could be obtained and the weld quality could be evaluated. Finally, many weld bead measurement and weld quality inspection experiments are conducted. Experimental results demonstrate that the developed structured light vision sensor and proposed methods could achieve satisfactory performance for weld quality inspection.

Novel projector calibration method for monocular structured light system based on digital image correlation

Monocular structured light system, which consists of one camera and one digital light processing (DLP) projector, is a simple and effective tool to acquire accurate three-dimensional (3D) shapes. But such high precision is only possible if the projector is accurately calibrated. Many of the existing projector calibration methods have complicated procedures or low calibration precision. In this paper, an accurate speckle-based feature points matching method is proposed to estimate the image coordinates of feature points in projection chip (digital micro-mirror device or DMD) plane. The method relies on an uncalibrated camera and makes use of affine transformation theory and two-dimensional digital image correlation (2D-DIC) method to reach sub-pixel matching precision. Considering the skew of the projection chip, a full-parameter calibration model is presented to describe the projector. A novel system is developed and series of validation tests were carried out to demonstrate the performance of the proposed method.

Attitude/Position Estimation of Rigid-Body using Inertial and Vision Sensors

This paper is concerned with the attitude/position estimation of a rigid-body using inertial and vision sensors. By employing the Newton-Euler method, a kinematic model is developed for the rigid-body by treating the inertial measurements as inputs. Based on the coordinate transformation, a nonlinear visual observation model is proposed by using the image coordinates of feature points as observations. Then the Extended Kalman filter (EKF) is utilized to estimate the attitude/position recursively. The effectiveness of the proposed algorithm is evaluated by simulation.

Pose Self-Measurement of Noncooperative Spacecraft Based on Solar Panel Triangle Structure

Aiming at the recognition and location of noncooperative spacecraft, this paper presents a monocular vision pose measurement method based on solar triangle structure. First of all, an autonomous recognition algorithm of feature structure based on sliding window Hough transformation (SWHT) and inscribed circle of a triangle is proposed, and the image coordinates of feature points on the triangle can be obtained relying on this algorithm, combined with the P4P algorithm and the structure of spacecraft, calculating the relative pose of target expressed by rotation and translation matrix. The whole algorithm can be loaded into the prewritten onboard program, which will get the autocomplete feature structure extraction and relative pose measurement without human intervention, and this method does not need to mount any markers on the target. Then compare the measured values with the accurate value of the laser tracker, so that a conclusion can be drawn that the maximum position error is lower than 5% and the rotation error is lower than 4%, which meets the requirements of noncooperative spacecraft’s pose measurement for observations, tracking, and docking in the final rendezvous phase.

Camera Calibration Method Based on Vanishing Point

We present a camera calibration method based on vanishing point, that is, the vanishing points of two groups of parallel lines on the target plane are used to achieve camera calibration. A series of known positions points on target plane are used as the feature points, and the target images are recorded, the image coordinates of feature points are used to calculate the coordinates of vanishing point, then the matrix between feature points and camera is used to obtain internal parameters of camera. Experimental results show that the proposed calibration algorithm is correct, simple and convenient.