Box Check

draw a box — see where your edges really point

round: –
score: –
best: –

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edges: 0

Drawing a box and checking where its edges point

You draw a box freehand, one straight stroke per edge — six at minimum, nine to twelve for a full one, lifting between them. Each edge is extended past its own ends the moment it is accepted, so where a line actually points is visible from stroke one. Checking sorts the strokes into three families by the vanishing point each set shares, marks those points and — when a real camera honestly fits your three sets — draws the box that camera would have seen, laid over yours. Tapping a critique row isolates one set.

The habit underneath is small: extend a line, look at where it goes. It answers the question a page of practice boxes cannot answer about itself — are my boxes converging? Edges that spread apart as they recede are the classic error — going away from you they should be closing in — which the drawn segment hides and the extension shows. Sorting goes by shared vanishing point rather than by angle on the page: under ordinary perspective one 3D direction can spread over 40° or more of image angle, which is enough to defeat any sort that goes by angle on the page.

How honestly a set converges

Each family is scored on how tightly its lines agree on one point; the round is the mean of the three, scaled by how complete the box is. Tolerance is stated in pixels of slop and converted to degrees at the edge lengths you drew: 6px of wobble is 2.3° on a 150px edge but 4.9° on a 70px one. It widens for the input in hand and never tightens past the old pen-tablet standard. The three sets are then held to what a box cannot fake: three mutually perpendicular directions seen through a pinhole leave three vanishing points on a triangle, and the camera's principal point has to be that triangle's orthocenter, with one focal length dropping out of it that fits all three pairs. If no real camera fits, those sets are not one box, however neatly any one converges. No AI and no model reads the drawing — the scoring is closed-form geometry: each stroke is reduced to its best-fit line, the lines are sorted by the point they share, and every number above is measured off those lines.

📦 Box Check

Drawing a box and checking where its edges point

How honestly a set converges

Box Check