基于射影变换圆阵靶标中心像点的计算

Calculation for imaging center of circular array target based projective transform

在基于圆阵靶标的视觉测量系统应用中,投影椭圆的几何中心并不是圆中心像点。为此,提出了一种基于射影变换的靶标圆中心像点计算方法。在完成退化椭圆边缘的亚像素坐标提取之后,该方法通过迭代的方式计算投影图像与生成的靶标规格相似图案之间的射影变换关系,可将退化椭圆边缘映射成较规则的圆。采用基于随机抽样一致(RANSAC)的圆拟合算法剔除异常点并计算圆心坐标,通过射影逆变换将其映射回原图像中,最终迭代收敛的圆心坐标点即为中心像点。仿真与实际实验均效果显著,从而验证了所提方法中心像点计算的有效性和准确性,并且可应用于众多视觉测量系统中,具有较强的实用性。

In the application of vision measurement system using circular array target, the projected ellipse geometric center is not the im- aging point of the circle center. Therefore, this paper proposes a calculation method for the imaging point of the target circle center based projective transform. After the extraction of the sub-pixel coordinates of degenerated ellipse edge, the proposed method calculates the projective transformation relationship between the projected image and generated pattern similar to the target with the way of iteration, and then the degenerated ellipse edge can be mapped into regular circle. After that, the circle fitting algorithm based random sample consensus （RANSAC） is used to eliminate the abnormal points and compute the center coordinates, and the center can be mapped back to the original image through the inverse projective transformation. Finally, the convergence circle center point of iterative process is the imaging center of the target circle. The simulation and actual experiment both achieve significant effect, which verifies the effectiveness and accuracy of the presented imaging center calculation method. In addition, the proposed method can be applied to various vision measurement system and has good practicability.