Trailer lower end coordinate calculation device, trailer lower end coordinate calculation method, and non-transitory recording medium

A trailer lower end coordinate calculation method comprising:

• acquiring images shot by a camera mounted on a vehicle towing a trailer via a tow bar at time points during a calibration travel of the vehicle;
• calculating coordinates of left lower end of the trailer, right lower end of the trailer, and hitch ball on the images, the left lower end of the trailer, the right lower end of the trailer, and the hitch ball being included in each of the images;
• transforming the coordinates of the left lower end on the images to the coordinates of the left lower end in a world coordinate system, transforming the coordinates of the right lower end on the images to the coordinates of the right lower end in the world coordinate system, and transforming the coordinates of the hitch ball on the images to the coordinates of the hitch ball in the world coordinate system;
• calculating a first average value which is an average value of a distance between the left lower end and the hitch ball in the world coordinate system during the calibration travel of the vehicle based on the coordinates of the left lower end and the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle, and calculating a second average value which is the average value of the distance between the right lower end and the hitch ball in the world coordinate system during the calibration travel of the vehicle based on the coordinates of the right lower end and the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle;
• removing the coordinates of the left lower end in the world coordinate system satisfying a first coordinate removal condition when the coordinates of the left lower end in the world coordinate system satisfying the first coordinate removal condition are included in the coordinates of the left lower end in the world coordinate system at time points during the calibration travel of the vehicle, removing the coordinates of the right lower end in the world coordinate system satisfying a second coordinate removal condition when the coordinates of the right lower end in the world coordinate system satisfying the second coordinate removal condition are included in the coordinates of the right lower end in the world coordinate system at time points during the calibration travel of the vehicle, and removing the coordinates of the hitch ball in the world coordinate system satisfying a third coordinate removal condition when the coordinates of the hitch ball in the world coordinate system satisfying the third coordinate removal condition are included in the coordinates of the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle;
• calculating the average value of the distance between the left lower end and the hitch ball in the world coordinate system or the average value of the distance between the right lower end and the hitch ball in the world coordinate system, an average value of an angle formed by the left lower end, the hitch ball and the right lower end in the world coordinate system, and an average value of the coordinates of the hitch ball in the world coordinate system, by using the coordinates of left lower end, the right lower end and the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle which are not removed;
• and
• calculating the coordinate of the left lower end in the world coordinate system at a predetermined time point after the calibration travel of the vehicle and the coordinate of the right lower end in the world coordinate system at the predetermined time point, based on a hitch angle of the trailer at the predetermined time point, the average value of the distance between the left lower end and the hitch ball in the world coordinate system or the average value of the distance between the right lower end and the hitch ball in the world coordinate system, the average value of the angle formed by the left lower end, the hitch ball and the right lower end in the world coordinate system, and the average value of the coordinates of the hitch ball in the world coordinate system.

A non-transitory recording medium having recorded thereon a computer program for causing a processor to perform a process comprising:

• acquiring images shot by a camera mounted on a vehicle towing a trailer via a tow bar at time points during a calibration travel of the vehicle;
• calculating coordinates of left lower end of the trailer, right lower end of the trailer, and hitch ball on the images, the left lower end of the trailer, the right lower end of the trailer, and the hitch ball being included in each of the images;
• transforming the coordinates of the left lower end on the images to the coordinates of the left lower end in a world coordinate system, transforming the coordinates of the right lower end on the images to the coordinates of the right lower end in the world coordinate system, and transforming the coordinates of the hitch ball on the images to the coordinates of the hitch ball in the world coordinate system;
• calculating a first average value which is an average value of a distance between the left lower end and the hitch ball in the world coordinate system during the calibration travel of the vehicle based on the coordinates of the left lower end and the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle, and calculating a second average value which is the average value of the distance between the right lower end and the hitch ball in the world coordinate system during the calibration travel of the vehicle based on the coordinates of the right lower end and the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle;
• removing the coordinates of the left lower end in the world coordinate system satisfying a first coordinate removal condition when the coordinates of the left lower end in the world coordinate system satisfying the first coordinate removal condition are included in the coordinates of the left lower end in the world coordinate system at time points during the calibration travel of the vehicle, removing the coordinates of the right lower end in the world coordinate system satisfying a second coordinate removal condition when the coordinates of the right lower end in the world coordinate system satisfying the second coordinate removal condition are included in the coordinates of the right lower end in the world coordinate system at time points during the calibration travel of the vehicle, and removing the coordinates of the hitch ball in the world coordinate system satisfying a third coordinate removal condition when the coordinates of the hitch ball in the world coordinate system satisfying the third coordinate removal condition are included in the coordinates of the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle;
• calculating the average value of the distance between the left lower end and the hitch ball in the world coordinate system or the average value of the distance between the right lower end and the hitch ball in the world coordinate system, an average value of an angle formed by the left lower end, the hitch ball and the right lower end in the world coordinate system, and an average value of the coordinates of the hitch ball in the world coordinate system, by using the coordinates of left lower end, the right lower end and the hitch ball in the world coordinate system at time points during the calibration travel of the vehicle which are not removed;
• and
• calculating the coordinate of the left lower end in the world coordinate system at a predetermined time point after the calibration travel of the vehicle and the coordinate of the right lower end in the world coordinate system at the predetermined time point, based on a hitch angle of the trailer at the predetermined time point, the average value of the distance between the left lower end and the hitch ball in the world coordinate system or the average value of the distance between the right lower end and the hitch ball in the world coordinate system, the average value of the angle formed by the left lower end, the hitch ball and the right lower end in the world coordinate system, and the average value of the coordinates of the hitch ball in the world coordinate system.