least-squares intersection — where it appears
Where parallel lines meet
They meet at a point that is not in the plane, and the horizon is the line made of all such points. Treating that as bookkeeping misses what it buys — a vanishing point becomes an ordinary point of the picture, findable from the drawn lines, checkable, and enterable into any calculation the others are.
The centre a scroll does not have
Fit a common point to the rays of one section of a handscroll and it misses by metres. The miss is not a residual to be tightened — it is exactly the standard deviation of the eye's own track, it grows linearly with how much is unrolled, and it goes to zero only for a section of no width.
Named alongside it
The objects these essays reach for when they reach for this one.
least squaresResidualcentre of projectionDemonstrationHandscrollHorizonline at infinityMoving viewpointPicture planepoint at infinityProjective planePushbroom