# The meaning of Grip point

As we know, the grip point often be used deform the surface or curve, but I confuse about the grip point and the control point of Nurbsurface? are they a same thing? in the other word, does the grip point equal to control point? if not, what math meaning of the grip point?

Yes they are the same. Grips are what you manipulate as user, and their location equals the controlpoint locations of the nurbs entity (curve, surface).

T
hanks Menno Dejj. But I have the other question.

Because Rhino not allow directly use the poly-surface to manipulate
the grip point(deform), so we must pre-explode the poly-surface become
to many small single surface.

If the edges are connect for original poly-surface, these edges
become split after moving grip points of each single surface (deformation).

How to solve this edge split phenomenon?

You may be more successful using the so-called “solid points”, using the command SolidPtOn .
Here you see the difference between “control-point” and “grip”. The control-point is only defined in the context of a NURBS object, and not for a polysurface. The “solid points” are nonetheless grips, which the user can drag to change the shape of a polysurface.

Thank you very much, but I still have two questions.

1. how to get these entity points like grip points using vb.net or vc
Dim ro() As Rhino.DocObjects.GripObject
ro = surface_paste(i).Object.GetGrips

2. These solid points look sparse, can it be dense? (If the deformation is large,more points are needed)

I’m not sure exactly how to do that from code, but if you have a `RhinoObject`, you can maybe call

``````RhinoObject obj; // obtained from document
obj.GripsOn = true;
GripObject[] grips = obj.GetGrips();
``````

As for the density, the solid points correspond to the polysurface vertices, i.e. the end points of edges. As far as I know these can’t be made more dense.