If we draw the perspective figure of a railway track, why does it seem to meet at a
point whereas the railway lines are parallel?
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Why railroad tracks seem to converge?
optics geometry
I stand up and I look at two parallel railroad tracks. I find that converge away from me. Why? Can someone explain me why parallel lines seem to converge, please?
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Aug 24 '15 at 15:23
Stefan
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Aug 31 '15 at 18:22
Qmechanic♦
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Because we live in a three dimensional world. – Horus Aug 24 '15 at 15:30
A more detailed explanation? – Stefan Aug 24 '15 at 15:32
Added an answer in the exact same question here: physics.stackexchange.com/a/292342/78842 – Aritro Pathak Nov 13 '16 at 15:00
I'm sure there's a proper answer but perhaps one could say - "parallel lines intersect at infinity". – Prahar Jan 1 at 13:21
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Keep in mind that your eyes perceive a fixed field of view. That is, you see a certain angle in front of you. They do not see a fixed distance across your line of sight. This means that the farther away for you you look, the more distance there is from one side of your FOV to the other. When you look at parallel railroad tracks that maintain a certain distance apart, they seem to converge as they go off into the distance. This is because the proportion of your field of view that the tracks take up diminishes.
Let's say the tracks are x meters apart and close to you, your FOV encompasses 6x meters across. That means 1/6 of your field of view is taken up by the tracks' separation. But far away from you, your field of view might encompass 600x meters across. This means the tracks would have converged to only take up 1/600 of your FOV. They're still the same distance apart, but the distance between them takes up less of your field of view. The brain interprets this as converging because if an image did this that was at the same distance in front of you throughout, it would actually be converging.
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Aug 24 '15 at 15:35
Jim
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The distance between the two is assumed to be constant. However, when you look at an object that is far away, it "seems smaller". What that means mathematically is that the angle from one end to the other, as seen at your eye, is smaller.
enter image description here
Now you can't tell the difference between something that is "small and close", and something that is "big and far". So the illusion presented by the railway track is that the distance between the rails gets smaller as you look at a point that is further in the distance.
And because your eye is a little bit above the ground, points on the railroad closer to the horizon are actually further away from you.