Rebuilding Control Vertices
You can rebuild the control vertices of a NURBS surface or spline.
If you have difficulties editing the control vertices of a surface or there are too many control vertices, you can rebuild a surface or curve with less control vertices in the U or V direction. The CVREBUILD command also allows you to change the degree of the surface or curve.
In the exercise file, click to select the middle control vertex on the left and then click the green Y-axis arrow on the Move gizmo to attempt to move the control vertex. The program immediately displays an alert to inform you that you cannot edit the control vertices of this surface. The information in the dialog also explains that you can use the CVREBUILD command to change the surface to degree 3 in both the U and V directions. Click Close to close the alert, and then press ESC to deselect the surface.
To rebuild the control vertices, on the Surface ribbon, in the Control Vertices panel, click the Surface – Rebuild tool. The program prompts you to select a NURBS surface or curve to rebuild. Click to select the surface or curve that you want to rebuild. As soon as you do, the Rebuild Surface dialog opens.
In the Control Vertices Count group box, you can specify the number of control vertices in the U and V directions. In the Degree group box, you can specify the number of control vertices available per span. The higher the number, the more complex the surface.
In the Options group box, when Delete original geometry is selected, the original surface will be deleted when you close the dialog. If you clear this checkbox, the original surface will be retained in the drawing along with the rebuilt surface.
If you select the Retrim previously trimmed surfaces checkbox, if the surface you are rebuilding had been trimmed, the areas trimmed from the original surface will also be applied to the rebuilt surface.
You can also see the Maximum Deviation between the original surface and the new one.
After adjusting these settings, click OK. The control vertices immediately update based on the new values, and the resulting surface in turn updates.
Source: Autodesk
