Use this function to modify the surface math basis of the selected surface from Bi-cubic spline to NURB or vice-versa.
Using the Function:
Select Refit from the Modify>Surface submenu.
The Convert and Refit Faces to NURBS dialog appears (see above). Configure the available dialog settings.
Select the closed boundary to be converted to NURBS.
Convert entire Body to NURBS – Will convert the entire solid or surface body to NURBS.
Convert selected Faces to NURBS – Will prompt you to select individual faces to convert.
Refit existing Spline/NURBS Faces - any surface in the partfile (cubic and NURBS surfaces) can be refit into a cubic surface with a more relaxed tolerance. The refit function is a way of smoothing the original surface and minimizing the number of patches that are needed to define the refit surface.
Curve fit tolerance - This is the maximum allowable deviation from the parent curves.