What is geometric perspective in photography?

Any object, which looks big near us and small far away from us, will gather more and more parallel contours. This convergence phenomenon is most easily seen by observing the two extended tracks on the train track, and the two tracks will gradually close together until they disappear. The point where parallel lines finally converge is called vanishing point. (This seems to be teaching non-Euclidean geometry! The vanishing point produced by lines parallel to the ground (such as railway tracks) must be on the horizon. The horizontal line drawn through this vanishing point is the horizon. In the picture below, the red parallel contour lines intersect at one point, that is, the vanishing point, while the blue line is the horizon. The vanishing point and the position of the horizon are two elements in the perspective relationship.