Interpolation using B-spline or Nurbs

Hi

I have three data sets inside a circle of radius 3m (Fig & data attached). I want to obtain the following two results

1. To make closed curve for each data set using spline or Nurbs.
2. To interplotate a number of such curves i.e. let say 10 such closed curve btw red & purple data set and 10 curve btw purple & green data set.

Please suggest how to do this interpolation using spline or nurbs