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?
I wonder how many things we're all going around doing badly because the idea of not knowing how to do them well seems too ridiculous to admit to.
...You've probably never been taught to have a conversation. I've had exactly one class on it and it was in the last six months. I know damn well that many people have not self-taught this well... In general there's this entire class of implicit skills that we mostly don't think of as skills, that we're entirely self-taught on, and that we practice sufficiently non-demonstratively that we can't easily watch what other people do. The result is a very personal skill idiolect.