Camera calibration and measurement using circular grooves inside pipes

A tele-operated robot should be used to maintain and inspect nuclear power plants to reduce the radiation exposure to the human operators. During an overhaul of the nuclear power plants in Korea, a ROV (remotely operated vehicle) may enter a cold-leg connected to the reactor to examine the state of the thermal sleeves and their positions in the safety injection nozzle. To measure the positions of the thermal sleeves or scratches from the video images captured during the examination, the camera parameters should be identified. However, the focal length of camera could be varied to a close up of the target and the aspect ratio and the center of the image could also be varied with video recording or digitizing devices. So, it is desired to calibrate the intrinsic parameters of the camera and digitizing device with the video images captured during the examination. In the video image of the safety injection nozzle, two or more circular grooves around the nozzle are shown as ellipse contours. In this paper, we propose a camera calibration method using a single image containing two circular grooves of the cylindrical nozzle whose radius and distance are known