Visual Plane
every picture states the point it is correct from
Concept

Demonstration — where it appears

2 essays name this object, across 2 fields. What follows is each of them, and the objects they name alongside it.
a room 2.8 m across, eye 1.6 m up1 mthe same plan, 137× bigger137 midenticalpicturesthe picture — both scenes, drawn twice, one on top of the otherlargest disagreement 1e-13 px over 8 verticesone length has to come from outside the picture

The one thing a single view cannot give

Make the world a hundred and thirty-seven times larger and move the eye a hundred and thirty-seven times further away, and the picture does not change by a measurable amount. Every ratio in a scene is recoverable from one photograph and no size is, and that is not a caveat about the method — it is the shape of the method.

metrology · scale the piazza, in planthe Baptistery, 25.6 m53 m27.2°the cathedral doorthe panel, and the eye it needsthe Baptistery fills 100%the eye is 60 cm back — off this sheet290 mm panel · 27.2° of Baptisterycorrect from 60 cm · 27° across

Brunelleschi drilled a hole in his panel

The first perspective demonstration in the European record came with its viewing point enforced — a hole through the back of the panel, a mirror held out in front, and one place to stand. That distance is computable from the panel's size and the angle the Baptistery subtends, and the answer lands squarely on the arrangement the account describes.

construction · station

Named alongside it

The objects these essays reach for when they reach for this one.

BaptisteryFocal lengthPeepholeProjective invariantReference lengthscale ambiguitySimilaritysingle-view metrologySubtended angleViewing distance

All concepts