The grating projection phase measurement method can obtain 3D surface profile of an object with a grating projection device and two cameras, which is widely used in reverse engineering, industrial detection, cultural relic digitization and human body measurement due to its simple measuring principle, convenient operation, fast and high-precision data acquisition of 3D point clouds. As one of its calibration processes, binocular vision calibration plays a key role in getting high-precision measurement results, and the accuracy of extracting feature points on the calibration target directly affects the binocular calibration accuracy. In this paper, a sub-pixel corner extraction method based on Shi-Tomasi algorithm was proposed to extract corner points of checkerboard. An experiment is done to compare the extraction effect of the proposed algorithm with the traditional Harris method. The experimental results show that the proposed algorithm can locate the position of corner points more effectively with higher extraction accuracy. The mean square value of the reprojection error is about 0.008 pixels, the rate of corner extraction is 74.6%, and the processing time is shorter, about 0.78 seconds. Therefore, the method used in this paper is reliable and feasible for the feature point extraction in 3D reconstruction of measured objects.
The three-dimensional measuring system based on structured light has the advantages of propermeasuring range, high speed and non-contact measuring mode，and it is widely used in medical and manufacturing fields. The strip center extraction is one of the key steps in the line structured light vision measurement system. According to the line structure laser measurement model, the essence of the line structure measurement is to extract the pixel coordinates of the laser beam and substitute them into the measurement mathematical model formula to calculate the spatial coordinates of the measured points. Thus the accuracy and precision of laser strip pixel coordinate extraction directly affect the final calculation results. When the laser is projected onto the surface of the object to be measured, it is susceptible by the surface material of the object, ambient light and other factors, which may lead to speckle, uneven brightness of the light, wide range of light width variation and other problems. In this paper, an adaptive method for extracting light strips is proposed to solve the problems of speckle and wide width range of the light strips.
Catenary is an important part of electrified railway, and its geometric parameters are important parameters reflecting the safe and stable operation of locomotives. With the improvement of its speed, there are higher requirements for high-accuracy and real-time detection of geometric parameters of catenary. The existing systems have problems of long sampling interval, low real-time performance, and light-sensitive. Aiming at the actual requirement of dynamic measurement of catenary geometric parameters, a non-contact catenary geometric parameter detection system based on machine vision was developed. Firstly, a measurement model based on high-power line lasers and high-resolution area cameras was established to meet the application requirements. The measurement principle of the system was analyzed and the detailed formulas were deduced. Secondly, image difference, laser spot roundness analysis and other image processing algorithms were used to quickly and accurately detect the characteristics of laser points on the contact line with complex background. Based on the measurement model and algorithms mentioned above, the hardware and software platform of the system were built, and fast image acquisition and processing was realized by using multi-thread programming technology on high-performance industrial computer, which solved the problems of long sampling interval and low real-time performance during the measurement. Real-time image storage and display and preservation of detection results were realized in the software. Finally, a preliminary experiment was performed on the prototype, and the accuracy of the measurement results was analyzed. Experiment results showed that the system works stably and has high accuracy, which meets the practical application requirements.