针对孔径测量检测效率低、检测精度受环境影响较大的问题，提出了一种基于二次曲线不变量测量孔径的模型，通过在孔表面的椭圆几何拟合获得被测孔的二次曲线不变量测量孔径。首先，建立世界坐标系并通过标定确定世界坐标系与摄像机坐标系之间的变换关系，采用改进的candy算法提取出孔边缘的亚像素坐标，并利用坐标变换关系将孔边缘的亚像素坐标投影到孔表面上；然后在孔表面上对孔边缘曲线进行椭圆几何拟合获得二次曲线不变量；最后在试验台上，利用二次曲线不变量视觉测量孔径，并与利用内径千分尺测量孔径的结果进行对比，检验了利用二次曲线不变量测量孔径模型的准确性。

A model of aperture measurement based on quadratic curve invariants was proposed to deal with the low detection efficiency and the problem that detection accuracy was greatly affected by the environment. The conic invariant aperture of the hole was obtained by ellipse geometry fitting on the surface of the hole. Firstly, the world coordinate system was established and the transformation relationship between the world coordinate system and the camera coordinate system was determined by calibration. The improved candy algorithm was used to extract the sub-pixel coordinates of the hole edge, and the sub-pixel coordinates of the hole edge were projected onto the hole surface according to the coordinate transformation relationship. Then, the ellipse geometric fitting of the hole edge curve on the hole surface was performed to obtain the quadratic curve invariant. Finally, the conic invariant was used to measure the aperture on the test bench, and the results were compared with those of the inner micrometer to verify the accuracy of the conic invariant model.