NURBS > Modify NURBS Patch Layer (selectable after NURBS > Fit Surfaces, but not for NURBS surfaces whose Fitting Method was Adaptive) modifies the smoothness of a NURBS surface by adjusting the number of NURBS control points and amount of tension on those points, one row of patches at a time. (A patch layer is a row of patches.)
After the dialog opens, click a patch in the Viewing Area. An entire row of patches will become selected. Modifications affect one row of patches at a time. Make changes, press Apply, and select another row if necessary.
The parameters are:
Control Points integer field - specifies the number of NURBS control points in the selected row of patches. NURBS control points are not the same as the grid count in each patch.
Surface Tension decimal field (0.0 to 1.0) - The lower the number, the more accurately the model represents original data. The higher the number, the smoother the surface appears, but some accuracy may be lost.
OK button - saves modified patches to the object and closes the dialog.
Cancel button - terminates the dialog without saving modified patches.
Apply button - generates a preview based on the Control Points and Tension values.