Meshes and Surfaces - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 416

Command: 3DEDITBAR
Select a NURBS surface or curve to edit:
Selection
Then, it prompts for a point on the surface, displaying two perpendicular red lines:
Select point on NURBS surface. Point
The 3DMOVE gizmo is displayed with three grips, which is explained next. Pressing
Enter ends the command. The Base point option allows selecting a different point
on the surface and the Displacement option allows defining a new base point by
projecting coordinates on the surface:
Select a grip on the edit bar or [Base point/
Displacement/Undo/eXit]<exit>: Selection or
Enter
There are three grips associated to the gizmo that allow shaping the surface:
• Square grip : This grip moves the surface or aligns its tangent (accessed
by the right-click button menu)
• Triangle grip : This grip allows choosing to move or to align the tangent
• Tangent arrow grip : This grip modifies the tangent magnitude