I have been following the slides from uzh on camera calibration(https://rpg.ifi.uzh.ch/docs/teaching/2020/03_camera_calibration.pdf) with direct linear transform.
On slide 33 they say that system should have rank 8 to have a unique(up to scale) solution for homography matrix.
$QH = 0$ where $Q\in R^{2n\times9},H\in R^9$
Values of Q are known. H - homography matrix, which we have to find. Why can we only find the solution up to scale? Can't we have an exact value for homography matrix?