Editing Surface Control Points
When you edit surface control points, you define the number of rows and columns in the surface mesh, and then select and move one or more of the points of intersection, called control points. The default surface mesh has 4 rows and 4 columns. If you select more than one point, the last selection is encircled in red to signify that it is the active point. Click another point in the selected group to make it the active point.
You can set movement constraints for the selected points, and then drag or nudge them. A nudge is an incremental adjustment. When you apply a constant movement constraint, all the selected points move by the same amount as the active point. A linear or radial movement constraint moves the selected points by a proportion of the distance you move the active point.
Surface mesh boundaries are automatically constrained with one of the following options:
Preserve Position
Preserve Tangency
Preserve Curvature
The default constraint corresponds to the surface connection type you set. When a boundary is constrained, you cannot edit its control points, and its connection to the neighboring surface is preserved. You can select a new constraint for one boundary, or you can clear all boundary constraints.