Caustic 1. Heart.
Caustic is a method of deriving a new curve based on a given curve and a point. A curve derived this way may also be called caustic. Given a curve C and a fixed point S (the light source), catacaustic is the envelope of light rays coming from S and reflected from the curve C. Diacaustic is the envelope of refracted rays (http://xahlee.info/SpecialPlaneCurves_dir/specialPlaneCurves.html). This applet illustrates catacaustic of a circle with light source not on the curve. The resulting curve is a Limacon Of Pascal, but with imagination .....