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’ve been looking at this chart a lot over the past few weeks.
It shows us that print ad budgets were doing just fine all the way though the first decade or more of the consumer internet. There was even a little spike upward for the Dotcom bubble. Then the financial crisis and recession of 2008/9 caused a step change down, but when the crisis was over the budgets didn’t come back. Instead, the market had been reset, and budgets have been falling steadily ever since.
You might call this the Will E Coyote effect - you’ve run off the cliff, or the cliff has disappeared from under you, but there’s a brief moment while your legs windmill in the air before gravity kicks in. It can take a while for the inevitable to happen, but then, as Lenin pointed out, you get a decade of inevitable in a week.