Nutello wrote:
I'm not quite sure how you found that principal point. Is it coincidence it's on the horizon? Does that mean the camera was perfectly horizontal?
This property is connected to a two-point-perspective. When the vertical lines are parallel, it is a two point perspective.
In a three point perspective the principal point is not on the horizon. Then there is a perspective triangle. The principal point is the orthocenter of this perspective triangle.
We can know the position of the camera, but we don't know of it is made with tilt-shift, corrected afterwards or cropped afterwards.