Distance point — where it appears
The point you have to stand at
A perspective picture is a projection through a centre, and scaling that centre's distance to the width the picture is actually shown at gives a distance in centimetres. Shown 160 mm wide, a 40° picture is correct from 22 cm and a 90° one from 8 cm. Nobody stands there, and that single fact explains most of what gets called distortion.
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.
Named alongside it
The objects these essays reach for when they reach for this one.
Focal lengthVanishing pointViewing distancecentre of projectionCentric pointdiagonal vanishing pointfield of viewHorizonMeasuring pointPrincipal pointResidualStation point