How to find the point of a Mediapipe Pose Estimation line that's on the edge of an OpenCV frame?

Question

In this picture, how can I get the x-y coordinates of the points in the red circles for the visible white lines?

I know how to find the landmark x-y points:

for i in results.pose_landmarks.landmark:
  if i.visibility >= 0.90:
    x = int(i.x*cols)
    y = int(i.y*rows)
    allpts.append((x,y))

But how can I get the (x,y) coordinates of the red points where the landmark for the end of the white lines are not visible in the frame?