nurbs surface: circle

[Arthur Clemens <aclemens@xxxxxxxxx>]

I have this code to create a nurbs circle outline:

#Inventor V2.1 ascii

Coordinate4 {
    point [ 1         0         0   1,
            0.707107  0.707107  0   0.707107,
            0         1         0   1,
           -0.707107  0.707107  0   0.707107,
           -1         0         0   1,
           -0.707107 -0.707107  0   0.707107,
            0        -1         0   1,
            0.707107 -0.707107  0   0.707107,
            1         0         0   1,        ]
}

NurbsCurve {
    numControlPoints    9
    knotVector  [ 0.00, 0.0, 0.0, 0.25,
                  0.25, 0.5, 0.5, 0.75,
                  0.75, 1.0, 1.0, 1.00 ]
}


... but I need to have a circle surface, too. The Inventor Mentor is not 
very helpful to me about nurbs, or I am being stupid.
Can anyone help me to convert this code to a NurbsSurface?

Arthur Clemens