250 Box Challenge - Inside lines don't create a corner as expected - why?

9:35 PM, Monday August 23rd 2021

While I've been working on my 250 box challenge, I've noticed an issue where even though my lines align well up to when I need to make my inner corner, the lines of the inner corner don't align as expected, creating three separate intersections instead of just one. I made two boxes using three pre-set vanishing points and a straight edge to illustrate my point.


Black lines are the concrete lines I used - They are the box. The red lines are the direction in which these lines should go towards their vanishing points. There are blue dots/circles to denote the expected intersections of the inside corner. For the inside corners I actually made on these boxes, I averaged the distance between the three separate intersections and then made blue lines to show the direction in which they vanish.

I was hoping for some explanation as to why this is happening, and if there is a way to fix it.

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12:20 AM, Tuesday August 24th 2021

Well firstly. If you're not using a ruler for the black lines then kudos. They are mighty straight and consistent.

Once you have completed the box you are supposed to extend the lines you have drawn, not create new ones. These should travel approximately towards a vanishing point. You appear to be marking the vanishing point and then drawing new lines from a corner edge to it. This is wrong.

We extend the lines to see how well the box edges converge to a single point but for most it is unlikely they will all meet exactly. Also, many times the vanishing point should not be on the paper but at some distance from it. Hence we are checking general overall convergence because there is no VP on the paper to draw to.

Remember this is an exercise in judgement and visualisation not geometric perfection. Might be worth reviewing the instructions for this exercise. Drawabox is very specific about what and how things should be drawn in each exercise. Hope this helps.

3:11 AM, Tuesday August 24th 2021

This isn't the method I'm using for the boxes I am using for the challenge - These were simply for a visual example, created using a ruler, as I said in my initial post. I used pre-set points for these boxes because my question could be illustrated most effectively in this fashion. This doesn't really answer my question of why the three lines that form the interior corner of the box don't intersect at a single point, but instead intersect three times, assuming all lines created preceding these final ones converge perfectly.

9:50 AM, Tuesday August 24th 2021

Perhaps labelling the question 250 box challenge has set me off on the wrong track in my sleepy state. Using a real example would be more useful as this doesn't reflect expectations of the challenge.

In your example I just think the corners aren't placed quite as accurately as you think. Take the bottom back corner point. It looks off or at least because the angle is shallow and the line is fairly thick the point where they intersect has a margin of error. If you compound small errors like this then they will tend to show up at the last point you attempt to determine.

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