Performing Perspective transform when not all corners are visible python openCV

Question

Im trying to do perspective transform on a video of a football pitch, I have found many resources for ways of doing this when all four corners of the pitch are visible however how can i do this when not all corners are visible? maybe a way of extrapolating beyond the video box?

Answer 1

Instead of using the four corners of the field, use the part of the field that is visible. In this image, the field is visible only to the 50 yard line.

Two corners and two midpoints are used to warp the image. Instead of warping the source image to the corners of the destination image; the source image is warped into two corners and two midpoints.

If 75% of the field is visible, warp the source image to the to that percentage of the destination image.

image source: https://www.coloradoan.com/story/sports/csu/football/2016/12/21/story-behind-boise-states-blue-football-field/95712824/