SISL is an open source project. It is a library of C routines to model NURBS curves and surfaces.
To use SISL, you first need to compile it and create a suitable python module. I have describedhow this can work in this file. Here, however, I did not use the whole SISL, but only the parts I found interesting. If you need additional functions, you have to include them separately (in s_declarations).
You will then get a library sisl.lib and then you will get the python module sisl_adapt.
Again afterwards you can use e.g. the python file SISLCall. The classes SislCurveHolder, SislSurfaceHolder and SislLoftedSurfaceHolder then allow a reasonably comfortable use of the SISL classes.
With the help of SISL you can of course easily calculate a point grid for the approximation of a surface.