High-speed distance measurement between moving vehicles with NIR-LED markers

An image-based technique with high measurement rate has been proposed to measure the distance between two moving vehicles. By combining several near-infrared (NIR) LED markers mounted on the forward vehicle with an NIR-filtered CMOS camera mounted on the backward vehicle, one can clearly recognize the marker shape and positions without any adjusting the focus lens of camera, and hence he can extremely reduce the time of digital preprocessing such as noise elimination and marker segmentation. The distance may be easily calculated from the geometrical transformation of the marker positions obtained in sub-pixel resolution from the gravity center of the pixel value. The image-based technique proposed here is actually examined in the vehicles moving on linear and curved tracks. It is experimentally confirmed that the measurement rate attains to 1000 frames/sec in the windowed image of 752 times 34 pixels, with a small processor with the clock of 600 MHz, including the capture time of the image, the calculation time of the gravity center, and the geometrical transformation time. The measurement error is less than 1 % for the distance range of 0.5 to 3 m.