Consider the diagram below:
We can see from the plane $\Phi$ two parallel lines on its surface. Then these two lines are projected onto the plane $\Pi$ where they appear to be intersecting.
My question is how did they become intersecting? and how is the perspective defined in this figure? that is to say from what field of view is the person looking at this diagram to see this phenomena? Because I don't understand what this diagram is specifically describing when it connects all these rays to the optical center $O$.
I have attached an example of train tracks and hope someone can help me understand it as an example of this phenomena