Interpolate Curve Not working (disappears on close)

Hi all,

I was wondering if anyone could help trouble shoot an issue with the interp curve command.
Rhino seems to be running fine, however when I try use the interp curve command when attempting to close the curve it disappears.
I have uninstalled and reinstalled rhino to no success and have attached reference photos.

Any advice would be greatly appreciated!

Thank you,


First thing to check is if you are not in Rendered display mode. By default, it doesn’t show curves (after they have been created). Switch to wireframe, the curve probably was created.

If the Rendered mode situation is not the case, please run the command SystemInfo in Rhino and copy/paste the results here.

Hi Helvetosaur!

Thank you for you help. The images above were done in shaded mode and I have retried in wireframe and unfortunately the issue is persisting.

Please find the system info command pasted below:
Rhino 6 SR28 2020-7-17 (Rhino 6, 6.28.20199.17141, Git hash:master @ b1f15b655bd1f5ae0d3d3257e3efdeb0a45630e4)
License type: Educational, build 2020-07-17
License details: Cloud Zoo. In use by: Zachari Orelowitz ()

Windows 10.0 SR0.0 or greater (Physical RAM: 32Gb)
Machine name: DESKTOP-G2NNH8J

Non-hybrid graphics.
Primary display and OpenGL: NVIDIA GeForce RTX 2060 (NVidia) Memory: 6GB, Driver date: 6-21-2020 (M-D-Y). OpenGL Ver: 4.6.0 NVIDIA 451.48

OpenGL Settings
Safe mode: Off
Use accelerated hardware modes: On
Redraw scene when viewports are exposed: On

Anti-alias mode: 4x
Mip Map Filtering: Linear
Anisotropic Filtering Mode: Height

Vendor Name: NVIDIA Corporation
Render version: 4.6
Shading Language: 4.60 NVIDIA
Driver Date: 6-21-2020
Driver Version:
Maximum Texture size: 32768 x 32768
Z-Buffer depth: 24 bits
Maximum Viewport size: 32768 x 32768
Total Video Memory: 6 GB

Rhino plugins
C:\Program Files\Rhino 6\Plug-ins\Commands.rhp “Commands” 6.28.20199.17141
C:\Program Files\Rhino 6\Plug-ins\WebBrowser.rhp “WebBrowser”
C:\Program Files\Rhino 6\Plug-ins\rdk.rhp “Renderer Development Kit”
C:\Program Files\Rhino 6\Plug-ins\RhinoScript.rhp “RhinoScript”
C:\Program Files\Rhino 6\Plug-ins\IdleProcessor.rhp “IdleProcessor”
C:\Program Files\Rhino 6\Plug-ins\RhinoRender.rhp “Rhino Render”
C:\Program Files\Rhino 6\Plug-ins\rdk_etoui.rhp “RDK_EtoUI” 6.28.20199.17141
C:\Program Files\Rhino 6\Plug-ins\rdk_ui.rhp “Renderer Development Kit UI”
C:\Program Files\Common Files\McNeel\Rhinoceros\6.0\Plug-ins\PanelingTools (6caed836-bc06-4ebc-b1fd-e10886a0dc94)\2018.12.17.906\PanelingTools.rhp “PanelingTools”
C:\Program Files\Rhino 6\Plug-ins\NamedSnapshots.rhp “Snapshots”
C:\Program Files\Rhino 6\Plug-ins\Alerter.rhp “Alerter”
C:\Program Files\Rhino 6\Plug-ins\RhinoCycles.rhp “RhinoCycles” 6.28.20199.17141
C:\Program Files\Rhino 6\Plug-ins\Toolbars\Toolbars.rhp “Toolbars” 6.28.20199.17141
C:\Program Files\Rhino 6\Plug-ins\3dxrhino.rhp “3Dconnexion 3D Mouse”
C:\Program Files\Rhino 6\Plug-ins\Displacement.rhp “Displacement”

OK, all that looks pretty good to me… don’t know what’s going on then. So the curves are not being created at all? Ctrl+A doesn’t select anything?

Hi, thanks again for your help.

Correct, no curve seems to be created. If I hit Ctrl+A the command line just returns ‘No objects added to selection’.

Is _InterpCrv the only curve command that is not working? For example does just _Curve work? _Polyline?


Polyline, Curve and InterpCurveonSurface all appear to be working fine. It’s just InterpCrv that isnt working atm.


Wow, that’s pretty odd.

I just re-read your first post -

Can you create an open curve?

Yes so odd! Open curves work fine, it is only when they close

Hi Helvetosaur,

I have found a partial solution. It appears that when the degree is an even number it will not allow the line to be closed, however when set to an odd number the line works as it should. Not sure why this occurs, any ideas?

Ahh, good catch - I see that here too. I never use even degrees above 2, but it I see it also fails with degree=2. I suppose this is a bug, unless there is some mathematical limitation - however as I can successfully close a degree 2 or 4 control point curve, I don’t think that’s it.

I created a bug track item for this:

Side note to @KelvinC - when looking in the help to see if there was some sort of built-in limitation on this I ran across this line:

Not sure how this applies here - it does apply to _Curve - as I can create for example a degree 5 curve with InterpCrv by picking only 3 or 4 points. Of course, those are not the control points, the curve created is indeed degree 5, but has 8 control points (open, 3 points picked) or 12 (closed, 3 points picked then close). So maybe the help item needs a bit better explanation.

Thank you for all your help Helvetosaur! I really appreciate it

The InterpCrv command in Rhino 5 only allows odd degrees.
RH-22340 added even degree support in Rhino 6.

I’ll do some test before changing the topic. Thanks.

Hey @KelvinC
This is not the same issue as RH-22340 - I tested in both V6 and V7 and it definitely fails with an even degree and a closed curve.

I meant to say it was not a problem in v5 because it was not possible to set even degrees. Like @mikko said in RH-22340, there could be bugs with even degrees and not be able to close the curve is one of them. Thanks.

Some more observation:
Curves with an even degree can be smoothly closed only when Knots=Uniform.
Curves with an even degree and Knots=<Any> can be closed when Sharp=Yes.

I think it is a bug rather than a limitation. So I don’t add a note to the topic about these things.

I changed the description of the degree option in the Curve and InterpCrv commands as below:

For Curve command
Specifies the degree of the curve.
The resulting curve will not be the degree you request unless the control point number is at least one more than the degree number.

For InterpCrv command
Specifies the degree of the curve.
Unlike the Curve command, the resulting curve is always the degree you request even if only two points (start and end) are picked.

Thank you.