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

Eye level — where it appears

The height of the camera's own centre, which every point of the picture on the horizon shares whatever the picture plane is doing. It is the one height in a scene a photograph gives away for nothing, which is why it is the first thing a single-view measurement establishes.

Named by 5 essays across 2 fields — each of them below, with the objects they name alongside it.

horizon3 vanishing points at a finite distance2564 px · 8129 px · 531 px

The horizon is at eye level — if the picture plane is vertical

The horizon cuts every standing figure at the same fraction of its height however far away it is, which is the most immediately usable fact in the subject. It holds when the camera is level, and a twelve-degree tilt is enough to spread the fractions by more than a percentage point.

construction · Eyelevel horizon = eye level, 1.60 m89.89%correct from 26 cm, at 160 mm widespread 0

The horizon, and the fraction

The horizon crosses every upright at the point of it that stands at the camera's own eye height — always, whatever the picture plane is doing. It crosses at the same *fraction* of the drawn height only when the plane is vertical: tilt by 6° and the fractions spread by 0.08 percentage points, tilt by 4° and 0.06. One statement is an incidence and survives; the other is a ratio and does not.

construction · Eyelevel the camera's horizoncorrect from 19 cm, at 160 mm wide46° across

A picture with nothing straight in it

Every construction on this site is handed the horizon, and a photograph of a crowd, a hillside or a curved façade has no straight edge to give it. What such a picture does have is repetition — and three things of one height put the horizon exactly where the camera has it, from the picture alone. Two things do not, and three standing abreast do not either, and both refusals are the reader's ordinary situation.

construction · Eyelevel horizoncorrect from 16 cm, at 160 mm wideeye at 1.20 m · 57% in the last tenth

Higher on the page, and where that stops being true

A pinhole's image height above the horizon falls monotonically with depth over the whole 2–400 m range sampled here, and 57% of that whole range lands in the ground's last drawn tenth — the accumulation the oldest depth convention is quietly built from. Above eye level the ordering inverts, and at eye level exactly, five different depths draw one height, a spread of 0.0e+0 px.

conventions · Diminution the heads' linethe horizoncorrect from 16 cm, at 160 mm wide59 px, 1.46 m at the far figure

Figures on a street that slopes

Equal-height figures have their heads on one line, and the taught rule says the line is the horizon. On a street rising at 8.33 per cent the heads are still collinear to 2.8e-14 pixels and the line is 58.9 pixels above the horizon — the street plane's own vanishing line. The taught rule loses 1.46 m of a 1.62 m figure at the far figure, and runs out of figure altogether at 19.4 m.

construction · Height

Named alongside it

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

HorizonGround planePicture planesingle-view metrologyVanishing pointForeshorteningVanishing lineAffine mapCamera tiltCollinearityConditioningCross-ratio

All concepts