A boat and a distant skyline

 A boat in the open sea and a distant skyline which is partly obscured by the horizon line.  This picture is often used as argument for a curvature of the Earth.  It  would indeed  be an argument for a spherical Earth, if light had been proven to be linear, and not curved as the celestial equator and the separation of stars show. What we are observing in images like these is the same principle at work as with the pole and the observer. Higher parts of the building have a larger circle of sight and reach the circle of sight of the observer; parts of the building that are below the horizon line have a smaller circle due to their smaller height and do not reach the circle of sight of the observer.

 There is also another principle of perspective at work in this picture: the horizon line divides the boat into two parts - the upper part of the sail is above the horizon line; the lower part of the boat is below the  horizon line, while the entire boat is visibly in front of the horizon line and therefore within the circle of sight. The reason for that  is in the shape of the observer's light body. The perceived horizon line is not  determined by the circle of intersection alone, but also by the contours of the light body. The horizon line starts at the origin of the light body and goes all the way down where it eventually intersects the surface, whereas the circle of intersection marks the final limit of the light  body. Everything within the light body is perceived below the horizon. Objects that are within the circle of sight and at the same time outside of the light body are perceived above the horizon.