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Thread: parllel lines

  1. #1 parllel lines 
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    can two parellel lines appear intersecting when viewed from some plane ie x-y plane etc


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  3. #2 Re: parllel lines 
    Forum Ph.D. Leszek Luchowski's Avatar
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    Quote Originally Posted by parag1973
    can two parellel lines appear intersecting when viewed from some plane ie x-y plane etc
    When you are looking at two parallel lines, think of a third line: parallel to those two and passing through your point of view (your eye).

    If this third line is within your field of view, you will see it as a point (you are looking at it head-on). In the image your eye sees, the original two lines will meet at that point.

    This is best seen when standing out on a vast flat open plain, on a road or a railway track. The sides of the road, or the rails of the track, will appear to meet on the horizon. Of course on our planet (or on any other spherical planet with a transparent atmosphere) the horizon is defined by the curvature of the earth, but if you were standing on an infinite plane there would still be a horizon, and parallel lines would appear to meet on it.

    But I cannot think of a way to see parallel lines as actually intersecting. Just meeting (their apparent "ends" at infinity touching each other).


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  4. #3  
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    thank you les. i was thinking along the same lines. i just wanted to confirm that the lines cannot be shown parallel from any plane.
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  5. #4  
    Forum Ph.D. Leszek Luchowski's Avatar
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    Quote Originally Posted by parag1973
    thank you les. i was thinking along the same lines. i just wanted to confirm that the lines cannot be shown parallel from any plane.
    What you mean "cannot be shown parallel"? In particular, what do you mean by "shown"?

    If you take a photo of two parallel lines by pointing the camera perpendicularly to their common plane (I mean straight down if the lines are on the ground), then they will come out as parallel in the photo.
    Leszek. Pronounced [LEH-sheck]. The wondering Slav.
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