Improve Constant Offset Surface by adding smoothing

[dpanici]

https://faculty.cc.gatech.edu/~jarek/papers/localVolume.pdf

occasionally the offset surface, in regions of large concavity, can have self-intersections and non-smoothness. It could be possible to, at each zeta plane in the input grid, construct a 1D spline curve, calculate its curvature, then smooth over points with curvature not matching that of the original points on the surface (similar to the picture from the attached paper). May have to also do smoothing in the toroidal direction as well.