Creating a sphere from a spline curve

[SilverTiger]

I'm good with geometry, but I've never delved into this part of it. I'm a 3d modeller and I'm trying to create a 3d polyhedron using heptagons, rhomboids, and pentagons and all I need to find out is the radius of the inscribed sphere I'm creating. I drew a spline curve to map the flattened sphere of it. Now all I need to do is create a sphere from the curve, and I have no clue how to do this. Can anyone help with this?

 

[Alfi]

What modeling program are you using?