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?
it is apparent that the unfolding of the design process assumed a distinctly episodic structure, which we might characterize as a series of related skirmishes with various aspects of the problem at hand.
As the scope of the problem became more determined and finite for the designer, the episodic character of the process seems to have become less pronounced. During this period a systematic working out of issues and conditions took hold within the framework that had been established. This phenomenon is not at all surprising when we consider the fundamental difference between moments of problem solving when matters are poorly defined and those with clarity and sufficiency of structure.
Within the episodic structure of the process, the problem, as perceived by the designer, tends to fluctuate from being rather nebulous to being more specific and well-defined. Furthermore, moments of "blinding" followed by periods of backtracking take place, where blinding refers to conditions in which obvious connections between various considerations of importance go unrecognized by a designer.