Contour generator — where it appears
Named by 3 essays across one field — each of them below, with the objects they name alongside it.
A wire with a corner in its shadow
A bent wire has no corner anywhere on it, and its shadow has one. The lamps that do it are not a coincidence — they are a surface in the room, two-dimensional, made of the wire's own tangent lines, and a lamp being carried across the room passes through it.
The edge of a shadow is drawn on the object
The outline of a cast shadow is the image of a curve, and the curve is on the caster. It is not painted there: it slides when the lamp moves, it is not the outline the camera sees, and the two coincide only in the arrangement where no shadow is visible at all.
A hole is not preserved
The shadow of a connected object is connected — always, at every lamp position, and for a reason with no geometry in it. A hole survives in neither direction: a ring's shadow closes up at a computable tilt, and an object with no hole in it casts a shadow that has one.
Named alongside it
The objects these essays reach for when they reach for this one.
ForeshorteningPoint lightShadow projectionConicDegeneracynecessary, not sufficientOcclusionUmbraConnectednessCuspProjective mapSampling grid