Hi Danny, just a quick note on continuity - when you have a curve that is a "single segment" (formed with only one single spline instead of multiple splines touching end to end), if it is the most common cubic curve than that does give you an internal G2 continuity throughout the whole spline unless there are special things like fully multiple knots or stacked control points.

That's for NURBS curves though - a "bezier curve" as often made by 2D illustration software is not as good for G2 continuity because it basically has fully multiple knots for every curve span.

It's pretty frequent for curvature combs to be somewhat misused and over obsessed with though - when the comb itself has cusp points in it, that is actually G2 continuity, that's when the curvature is equal at a juncture point.

When the comb is completely smooth throughout, that actually means G3 continuity, where the rate of change of the curvature is continuous, not just the curvature itself being continuous.

There is not really as much of a physically noticeable difference between G2 and G3 continuity like there is between G1 and G2 with reflection lines.

The other thing is that it can often be better to be more concerned with "fairness" rather than the actual technical continuity. Pieces can be technically continuous but still have poor curvature distribution. Continuity is about how things match up at a certain point but not really about how they are distributed which tends to be actually more important in shaping.

- Michael