Cusps

The alternative to a smooth curve is to have a node that comes ‘in’ from one direction, but leaves in another. This is a ‘cusp.’ Cusps are important, as they make the hard turns where curvy bits intersect – such as the top of a heart or in shapes of leaves, or almost anything in nature.

A cusp allows you to have two curves come together on either side of a point. For instance the apex in the top, center of a heart-shape is a cusp. Traditionally digitizers would make a curve that falls just short of the cusp and then make a line to the cusp, and then they would begin a new curve going off to the other side. This has the negative effect of that hard line being visible, especially when scaled. It also produces a needle penetration where it isn’t needed. We’ll discuss more on this later.