Receiving surface — where it appears
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
A floor anamorph is three numbers
An anamorph is described everywhere as a picture stretched until only one viewpoint can read it, which says what it looks like and nothing about what it is. Cast one onto a floor and fit a map to the marks, and the map turns out to be a planar homology — a line of fixed points, one point off it, and a single ratio. Those three numbers are not a description of the eye. They are the eye.
The ceiling that is not a plane
Paint the same design for the same eye onto a floor and onto a barrel vault, then fit the best possible homography to each set of marks. On the floor it misses by femtometres, because the map is a collineation and four marks determine every other. On the vault it misses by half a metre, and no choice of four marks helps — which is where the projective machinery this site has used since its first phase stops applying.
Named alongside it
The objects these essays reach for when they reach for this one.
AnamorphosisCollineationDemonstrationHomographyPlanar homologyProjective mapStation pointArea scaleCatoptric anamorphosisCentral collineationCharacteristic ratioCross ratio