Abstract: Liquid location is a very important step in the liquid detection.By the camera angle of erection and the container，the liquid of rounded container in the image is similar to parabola.An algorithm is proposed to detect the liquid of rounded container in this paper.Edge detection，gray scale projection，Hough transform is used for estimating the coarse location and fine location of liquid.The time and spce complexity is reduced by using coordinate transformation.As compared with other traditional methods，this method is much easier and can be used broadly.Experiment results show that the method is effective.

Key words: coordinate transformation, Hough transform, parabola

摘要： 液位定位是液位检测中的重要环节。圆形容器中的液位由于受到摄像头架设角度和容器的影响，在图像中是一条近似于抛物线的曲线。提出了一种圆形容器中液位定位算法。该算法合理运用了边缘检测、灰度投影、Hough变换等方法实现了对液位的粗定位和精定位，并在检测过程中，根据液位线的特点，利用坐标变换将液位线变为标准的抛物线，减少了Hough变换参数空间的维数，提高了检测速度。该算法与传统的算法相比较，简单易行，适用范围广。实验证明了该算法的有效性。

关键词: 坐标变换, Hough变换, 抛物线