板料成形应变测量中方网格图像的亚像素匹配

针对板料成形应变测量中应用的方形网格，提出一种网格图像亚像素匹配法. 采用二值化和细化等方法得到网格线条的细化图像，然后通过初、精两次定位提取网格节点的亚像素图像坐标，并建立各节点之间的拓扑关系. 在已知各次拍摄时相机位置与姿态的基础上，根据网格节点的拓扑关系和极线约束实现同名网格节点自动匹配. 实验结果表明，所有匹配点对之间极线距离的平均值约为,0.17,像素时，匹配稳定可靠. 匹配结果可作为后续应变计算的基础数据.

Sub-pixel Matching of Square Grid Images for Strain Measurement in Sheet Metal Forming

We propose an algorithm for square grid image matching to be applied to the measurement of steel forming strain. The thinned image of grid lines is obtained with image binarization and thinning. A coarse-to-fine algorithm is executed to extract the sub-pixel image coordinates of grid nodes and establish topological relationship between nodes. An automatic matching algorithm is proposed to establish correspondence among grid nodes in multiple images according to the topological relation and epipolar constraint based on the known camera position and orientation in each shot. Experimental results show that the average epipolar distance of allmatching points is approximately 0.17 pixels, and the matching method is stable and reliable. The results can be used in the subsequent strain calculation.