Thank you for that link.

This is the problem…

Its not open. Its closed… but not to the satisfaction of the algorithm at the tolerance of .001

So far a weeks work working back through the model to solve this

The problem is projecting a smoothed curve onto another curve (in this case a bunch of isocurves) such that the projection happens at a Normal to the target curve. This requires deriving a construction plane for the curves, finding the intersection of a curve with that CP then vectoring the point normal to the curve. This could be created by using the closest point between the two curves, on each curve.

It would be nice if there was a command or GH module for this.

The highlighted points are the ones that intersect. The rebuilt curve introduces a smooth fit at the expense of following the isocurves. This could be done by making a surface of the isocurves and then using PULL, but the boundary conditions are complex and a surface introduces another layer of smoothing and errors that cause joins and merges to fail later.

PROJECT CURVE ONTO CURVE would be useful.