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

Transversal — where it appears

2 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
the panelhorizon — the centric point's heightthe section — the eye, the panel, the ground470 px — the viewing distancethree routes agree to 6e-14 pxsection, distance point, and a pinhole camera

Alberti draws a pavement, and chooses where the reader stands

The costruzione legittima of 1435 is exact. Run as a construction — with drawn rays and drawn intersections rather than the formula it turns out to satisfy — it agrees with a pinhole camera to six parts in a hundred trillion of a pixel. And it has one free parameter that the recipe never names, which is the distance from the eye to the panel.

construction · alberti centric pointdistance point, 12 px off the sheet →430 pxcorrect from 10 cm at 160 mm wide47° across

The distance point is the viewing distance, drawn

There is exactly one place in the whole classical apparatus where the distance from the eye to the picture appears as a length on the page, and it is the offset from the centric point to the distance point. Everything this site exists to compute was drawn in the fifteenth century, on the horizon, and nobody said what it was.

construction · alberti

Named alongside it

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

Centric pointFocal lengthHorizonViewing distancebracciocostruzione legittimadiagonal vanishing pointDistance pointGround lineLateral sectionMeasuring pointPinhole

All concepts