Interpolations need the `scipy python module <http://www.scipy.org/>`_.
To enable it just specify the interpolation type to:
- linear
- nearest
- zero
- slinear
- quadratic
- cubic
- krogh
- barycentric
- univariate
- or an integer representing the order of the spline interpolator
For more info see `interp1d definition on scipy <http://docs.scipy.org/doc/scipy/reference/generated/scipy.interpolate.interp1d.html#scipy.interpolate.interp1d>`_