How to establish a third vanishing point?
https://www.reddit.com/r/ArtFundamentals/comments/v6hdhz/how_to_establish_a_third_vanishing_point/
2022-06-07 00:00
quietcloudnotloud
Hello,
I know that in 2 point perspective the 3rd vanishing point is at "infinity" meaning that I can basically draw the vertical lines of the box without convergence. But I'm wondering when looking at the edge of a box and then moving it up and down, at which point do I need to establish/think about the location of a third vanishing point and until which point is the third vanishing point still at "infinity"? Is there a more precise rule than "when looking at the edge of the box"?
Uncomfortable
2022-06-07 19:55
Vanishing points go to "infinity" only when the orientation of the edges it controls in 3D space align perpendicularly viewer's angle of sight - basically when those edges run across their field of view, not slanting towards or away from them through the depth of the scene.
By that definition, technically as soon as your object slants slightly on a certain axis, you're going to have to deal with a concrete vanishing point. That is at least what is "correct" - but there are plenty of situations where we choose to fudge the rules a bit, and force a situation like that into having infinite vanishing points when we're composing our own illustrations.
Therefore in practice there's no clear answer to your question - there's a grey area where we can apply one or two point perspective and still have it feel okay, but the further out we drift, and the more noticeable the slant away from that perfect alignment with the viewer becomes, the more distortion you're going to run into.
quietcloudnotloud
2022-06-08 00:43
oh i think i get it, thank you :)