Converts a curve between open and closed/periodic.
Edit Curves > Open/Close Curves >
Select the amount of shape preservation when a curve is opened/closed.
Ignore does not preserve the shape of the original curve.
Preserve adds or deletes control vertices as necessary to preserve the shape of the original curve. This is the default setting.
Blend tries to create continuity on the resulting curve. It uses the Blend Bias for the amount of smoothing.