Extracting the navigation path of a tomato-cucumber greenhouse robot based on a median point Hough transform.

• A median point Hough transform with a maximum error of 0.5°was proposed. • Based on the 2G-B-R factor, a new grayscale factor is proposed to realize the segmentation of crops and soil. • Get the coordinate of the navigation points through the relative coordinate center of the pixel. The extraction of navigation paths is essential for the autonomous navigation of an agricultural robot. As most of the current navigation path extraction algorithms are time-consuming, difficult and susceptible to interference, the median point Hough transformation algorithm was proposed in this paper based on an optical system to fit the navigation paths of a greenhouse tomato-cucumber spraying robot quickly and accurately. The algorithm consists of four parts: interception of the target area, image segmentation, navigation points extraction and navigation path fitting. Image segmentation was based on the improved grayscale factor and Otsu method to achieve the segmentation of soil and plants. The navigation points then were extracted based on the relative coordinate center of the white pixel points of the binary image. Finally, the navigation path was fitted by the median point Hough transformation method. The experimental results show that the maximum error of the navigation path fitted by the improved Hough transformation was 0.5° and the time taken was 7.13 ms, which is 45. 24 ms faster than the traditional Hough transform and on average 5.1° more accurate than the least squares method. [ABSTRACT FROM AUTHOR]