摄影测量中圆形目标中心像点计算方法研究

Research on calculation method for the projection of circular target center in photogrammetry

空间圆圆心的像点位置计算是摄影测量系统开发的关键问题之一。透视投影变换把空间圆映射为像平面上的椭圆,而圆中心的像点往往并不是投影椭圆的几何中心。通过分析透视投影过程中的像点误差,提出了一种计算圆中心像点的方法。首先利用空间矩算子对目标投影轮廓进行亚像素边缘定位,接着以光心为顶点、理想的投影轮廓为准线建立椭圆锥,然后在该椭圆锥内构造与之具有投影关系的两个空间圆,并计算它们的法向及中心像点,最后根据标记目标的匹配关系来确定空间圆的平行圆,进而得到其法向以及中心像点位置。实验结果表明,该方法实现了圆形目标中心像点的精确定位,有效提高了三维坐标的重构精度。

How to calculate the projection of spatial circle center is one of the key problems in the development of photogrammetry system.Perspective projection maps a spatial circle to an ellipse in image plane,but the ellipse center and the projection of the circle center are not the same in image plane.Based on the analysis of the bias between the center of the projection and the projection of the circle center,a method for precisely calculating the projection of spatial circle center is presented.First,the sub-pixel edge of the projection profile is extracted using spatial moment operator,and an elliptic cone can be established using the optical center as the vertex and the ideal projection profile as the directrix.Then,two circles are constructed in the elliptic cone,which have the same projection profile.And then the center projection and normal direction of each circle can be calculated.Finally,the circle parallel to the spatial circular target is determined using the matching relationship of the reference targets,and hence the center projection and normal direction of the circular target can be obtained.Experimental results show that the proposed method achieves center location with high precision,and thus improves the accuracy of reconstructing 3-D coordinate effectively.