Catoptric anamorphosis — where it appears
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
The cylindrical mirror unbends it
Put a mirrored cylinder in the middle of the sheet and the light path from the eye to the paper bends once. The map that results is not a homography and not a projection in the plane sense at all — it varies its scale by a factor of seven across the design, which is why the smear is unreadable and why the mirror can put it back.
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.
Area scaleAnamorphosisAzimuthCatoptricCollineationCross ratioCylindrical mirrorDemonstrationHomographyLight pathPicture surfacePlanar homology