Piecewise map — where it appears
Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.
A shadow across an edge
A straight rod's shadow crossing the crease between floor and wall is two straight pieces, each dead straight to 1e-15 m, meeting at 35.08°. The corner is a fact about the room and not about the rod. Fit the floor's map from four marks and apply it across the whole shadow and the part on the wall comes back up to 78.9 cm from the object — the wrong map, applied confidently.
The anamorph that crosses a corner
Cast one design onto a floor and the wall at the end of it, from one eye. Each plane gets a collineation of its own; the two agree on the line where the planes meet, exactly, because a point of that line is a point of both. What they do not agree about is scale — the design runs 7.8 times its own size along the floor and 2.0 times up the wall, and the jump at the join is a factor of 3.9.
Named alongside it
The objects these essays reach for when they reach for this one.
AnamorphosisAxis of a homologyCollinearityCollineationContinuityDemonstrationDihedralGrazing incidenceGround planeHomographyHomologyPicture plane