Optimizing Hough transform for fertilizer spreading optical control

In Europe, centrifugal spreading is a widely used method for agricultural soil fertilization. In this broadcasting method, fertilizer particles fall onto a spinning disk, are accelerated by a vane, and afterward are ejected into the field. To predict and control the spread pattern, a low-cost, embeddable technology adapted to farm implements must be developed. We focus on obtaining the velocity and the direction of fertilizer granules when they begin their flight by means of a simple imaging system. We first show that the outlet angle of the vane is a bounded value and that its measurement provides the outlet velocity of the particle. Consequently, a simple camera unit is used in the vicinity of the spinning disk to acquire digital images on which trajectory streaks are recorded. Information is extracted using the Hough transform, which is specifically optimized to analyze these streaks and to measure the motion of the particles. The optimization takes into account prior mechanical knowledge and tackles the problem of Hough space quantization. The method is assessed on various simulated images and is used on real spreading images to characterize fertilizer particle trajectories. (c) 2006 Society of Photo-Optical Instrumentation Engineers.