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

Station — the ladder

2 distinct arguments against one idea, from the one that introduces it to the one that assumes the rest.
  1. the picture, 160 mm wide22 cm40°the eyefocal length 948 px22 cm at 160 mm wide

    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.

    rung 2 · viewing
  2. 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.

    rung 3 · construction

All ladders