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

Sensitivity — where it appears

2 essays name this object, across 2 fields. What follows is each of them, and the objects they name alongside it.
00.50011.502-0.400-0.20000.200k₁departure of the cross-ratio from the world's value (%)pinhole1.29%the pinhole's own error, on the same four points2e-16 — the control

A lens destroys the invariant

The cross-ratio is the one thing a projection preserves, and everything checkable on this site is checked with it. A lens returns it one and a third per cent out where the pinhole is exact to fifteen digits — and the height error that follows tracks a quantity nobody would guess.

lens · distortion 05101550100150200distance from the camera (metres)error in the recovered height, per pixel of click error (%)6 m — 0.55%25 m — 2.27%60 m — 5.43%120 m — 10.84%one pixel, on a 690 px picturelinear in distance

How wrong a measurement from one picture can be

The formula divides by a difference of two nearly equal numbers when the object is tall, which looked like the instability and is not. Measured, a taller object is recovered better and a more distant one worse — half a per cent per pixel at six metres and eleven per cent at a hundred and twenty. The argument that was wrong is as much the finding as the curve that replaced it.

metrology · height

Named alongside it

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

Cross ratioerror propagationHorizonsingle-view metrologyVanishing pointConditioningFocal lengthPrincipal pointProjective invariantRadial distortionResidualvertical vanishing point

All concepts