How do I extract the control curves and control points ！

Rhino Rhino for Windows
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1

As shown in the image, how do I extract the control curves and control points that define this object?

如何提取控制线 点
如何提取控制线 点565×601 82.5 KB

2

You can use these commands:

_ExtractControlPolygon ( menu: Mesh > From NURBS control polygon )

this will give you a mesh of the control points

Then:
_ExtractPt ( menu: Curve > Curve From Objects > Extract Points )

3

Thank U~

4

Oh, and the lines between control points:

_DupEdge on the mesh ( menu Curve > Curve From Objects > Duplicate Edges )
(use window select to select all mesh edges to duplicate).

5

Or use the new command “MultiExtract”, which has the following Command line options to extract any combination of:

ControlPoints=Yes (extracts the control points)

ControlPolygonEdges=Yes (extracts lines representing the control polygon)

ControlPolygonMesh=Yes (extracts the control polygon as a mesh object)

Linetype=Dashed/Solid/others (only shows when the “ControlPolygonEdges” option is active; adds a custom linetype to the extracted lines of the control polygon)

Group=Yes (groups the output objects separately, i.e. one group for control points, another group for control polygon edges in case that both options are active)

DedicatedLayer=Yes (places the output objects into their own layer named “Extracted control polygons”)

Color=White (choose from several basic pre-set colours)

6

Just to be clear: Rhino does not have a MultiExtract command, looks like this is wishful thinking (nothing wrong with that, but it may confuse others who read this topic).

I have created a ticket for extending ExtractControlPolygon https://mcneel.myjetbrains.com/youtrack/issue/RH-96731

7

Apologies about the confusion! I meant a new future command, not an existing one. My proposal is to expand the capability of the existing _ExtractControlPolygon command, because the users could benefit a lot from more granular options. These seem to be fast and easy to implement even in Rhino 9 Beta.

I’m adding another proposal to my previous post above (linetype for the extracted control polygon lines).

I often end up combining two or more commands just to extract the control polygon either as points, as lines, or both. It’s a bit repetitive process.