Okay, as long as this thread is migrating into perspective, there are two things I'd to offer:
1.) If your hypothetical camera on the scene uses something other than a 50 to 55mm lens—such as a 28mm wide angle—perspective lines are going to bend and throw your calculations off because a sort of hyper-perspective is being viewed, angles our naked eyes are not familiar with.
2.) I did a quick drawing of examples of 1, 2, and 3 point perspective, with the backsides represented as dashed lines.
At some point, you might want a little artistic sensibility leak into this geometric true-ism. 1 point perspective art can be interesting, like standing on a railroad track (while there is no train coming), and photographing straight down the vanishing point, the point where the rails seem to converge. Other than that, I'm hard pressed to think of a visually interesting 1 point perspective piece.
I usually aim for 3 point because that isa the maximum number of viewable sides without animating the object, but 2 point is useful and can be quite interesting if you make the sides semi-transparent.
My Best,
Gary
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