Football Playing Field Registration Using Distance Maps

In football, the playing field registration problem can be thought of as the homography estimation between the playing field plane and the visible area of the image. Existing approaches rely on the identification of significant keypoints in the image, such as the corners or intersections of the playing field lines, which are then used for the initial estimate of the homography. Finding the exact location of such keypoints can be very challenging, and that is why the initial homography estimates are not accurate enough and need to be refined iteratively. We propose distance maps, a technique that utilizes distance transform to predict the location of imaginary lines spread evenly over the playing field. Intersections of these lines can be used to find more accurate homography estimates. We also introduce the Calib360 playing field registration dataset, that can provide a sufficient amount of training data with accurate ground truth labels. All data and source code can be found at https://vgg.fiit.stuba.sk/field-reg.