In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light.
A piece of milled plexiglass acting as a projecting lens; via the Computer Graphics and Geometry Lab at the École Polytechnique Fédérale de Lausanne
New milling techniques applied to glass and plexiglass panels could be used to “create windows that are also cryptic projectors, summoning ghostly images from sunlight.”
[Pauly and Bompas] hope that the technique will be used in architectural design, to create windows that mould sunlight and throw images or patterns onto walls or floors,” which, if timed, milled, and manipulated just right, could produce a slowly animated sequence of images being projected by an otherwise empty window during different times of day.
To control the shape of a caustic pattern generated by a specular or refractive surface, we need to solve the inverse problem: how can we change the surface geometry, such that incident light is redirected to produce a desired caustic image?
Arturo Soria y Mata, who proposed a linear streetcar suburb for Madrid in 1882 and managed to build something like three miles’ worth of an intended thirty. Likewise, the project by Edgar Chambless for Roadtown, published in 1910, depicted an infinitely long, two-room-wide building atop three levels of underground rail lines for express, local, and freight traffic. In the late 1920s, N. A. Miliutin proposed a Soviet Union–spanning linear plan that—following Soria y Mata’s rhetoric—would have solved the old Marxian chestnut of city/country contradiction at a stroke. Le Corbusier’s Algiers scheme of 1933—a highway-topped fourteen-story building meant to stretch miles along the Mediterranean and house 180,000 people—was surely the most immediate precursor of Rudolph’s “City Corridor.”