基于抛物线拟合的十字激光图像屋脊边缘检测

A Roof Edge Detection Method Based on Parabola Fitting for Cross Laser Image

针对工程测量中对十字激光图像交点和倾角检测精度要求较高特点,提出了一种十字激光图像亚像素屋脊边缘检测方法。在十字亮条有用区域内,首先利用局域亮度极大方法检测亮条像素级屋脊边缘点;然后提取像素级边缘点水平或垂直方向上一定范围内的像素点亮度进行抛物线拟合,计算亚像素边缘点坐标;最后利用最小二乘法拟合出两条直线,计算十字交点及横亮线倾角。对距离光源4.5m处连续拍摄的50幅图像(图像分辨率为640pixels×480pixels,光靶分辨率为0.0827mm/pixel)进行了处理,十字交点x方向标准差为0.0134mm,y方向标准差为0.0158mm,横亮条水平方向倾角标准差为1.950′,精度明显优于像素级边缘点。该方法应用于导轨直线度和扭曲度检测仪中,取得了很好的效果。

In view of the high precision requirement on the intersection point and the angle of cross laser images used in industrial applications, a sub-pixel roof-type edge detection method is proposed for cross laser images. In a serviceable area, pixel-level roof-type edge points of bright strips are firstly detected based on maximum intensity in a local region. The sub-pixel edge point is then calculated by parabola fitting of the luminance of all pixel points near a pixel-level edge point in a certain range of horizontal or vertical direction. Finally, two lines of the cross laser image are fitted by least square method, and the intersection point and the angle of horizontal line of the laser image are calculated. For 50 samples （with a 640 pixelsx480 pixels camera and 0.082 7 mm/pixel as resolution of the target） at distance of 4.5 m, the standard deviation is 0.013 4 mm for x, 0.015 8 mm fory and 1.950＇ for angle, much better than that of pixel-level edge points. This method is used in straightness and twist-degree inspection system for rail guides and gets satisfactory results.