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

pole and polar — where it appears

The correspondence a conic sets up between points and lines, in which the pole of a plane's vanishing line is the image of a circle's centre.

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

centre of the ellipseimage of the centrecorrect from 22 cm, at 160 mm wideoffset 21.1 px

The circle whose centre moves

The image of a circle is an ellipse, and the image of the circle's centre is not the centre of that ellipse. The gap is 3 or 4% of the ellipse's width in an ordinary view — large enough to see, small enough to be dismissed as a slip by anyone not expecting it, and the reason drawn wheels look wrong.

foundations · conic centre of the ellipseimage of the centrepole of the horizon — 1e-13 px awaycorrect from 22 cm, at 160 mm widepole 1e-13 px from the truth

The centre, got back out of the picture

The image of a circle's centre is not the centre of the image ellipse — this site measured the gap four phases ago and left the obvious question unanswered. It has an exact answer, it needs a straightedge and the horizon, and it is one sentence: the image of the centre is the pole of the vanishing line with respect to the image conic.

foundations · conic

Named alongside it

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

ConicHorizonline at infinityComplete quadrangleEllipse fitForeshorteningHarmonic conjugateInverse projectionMidpointMinor axisPicture planeProjective invariant

All concepts