signed curvature

[ddudt]

Our curvature compute quantities are always positive. It would be useful to define a signed curvature to distinguish between convex and concave shapes. This should be particularly easy to implement for the FourierPlanarCurve class. We could either:

• Update the FourierPlanarCurve compute quantity to be the signed version, leaving all of the other curves with the positive version. Or
• Add a new compute quantity for "signed curvature" or something, which is not implemented for the other curve types (return NaN?)

[dpanici]

I think that having the quantity just for the FourierPlanarCurve makes sense, and then the Objective for it could just throw a NotImplementedError if any coil is passed in which is not a FourierPlanarCurve?

[dpanici]

Dot curvature vector with centroid to get signed curvature for every type