Forced perspective — where it appears
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
Also named here as viewing tolerance — the same set of essays touches all of them, so they are one junction rather than several.
Where the anamorph still works
A picture correct from one point raises an obvious question that nobody answers with a number — how far may the eye move. The answer here is exact rather than approximate: a wrong viewpoint composes the intended picture with a central collineation whose axis is the line the picture stands on, so the error is zero along that line and grows linearly upward, and a step sideways costs precisely as much as the same step upward.
A set cut for one eye
Build a colonnade four metres deep and cut every column so that its picture is the picture of one eighteen metres deep. The taper is forced rather than chosen — height and width both scale as the real depth over the intended one — and the match from the design eye is exact to sixteen decimal places. What gives it away is the second eye, and not by the ratio anybody would predict.
Named alongside it
The objects these essays reach for when they reach for this one.
AnamorphosisDemonstrationFree parameterStation pointViewing distanceViewing toleranceCentral collineationCharacteristic ratioCollineationDepth compressionDepth cueDiminution