SubD Curvature Graph and Surface Curvature Analysis Please

As I am testing out SubD for ship hull modeling, it is essential to have curvature graph analysis and surface curvature analysis. Otherwise hull fairing is not possible from a professional point of view.

When will SubD curvature analysis features be implemented?


It should work , we’ve asked a year ago :wink:

This is mine:
Wip7 Subd doesn't show the curvature

This is @gustojunk:

Thank you for your reply Skysurfer,

Yes the Zebra and Emap works, but curvature grpah and Surface Curvature with Gaussian etc. doesn’t.

So I am curious about a reply from a developer.

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Hoi Gerard -

As you saw from the links that skysurfer posted, curvature analysis is on the list as RH-50501.
The curvature graph request is on the list as RH-58162.
Both are public and have release targets set. As always, these are subject to change at any time.
I have added your vote to both feature requests.

Thank you Wim,

Can you also please add this ancient post wish to the pile: Curvature Graph improvements for Surfaces

Is there any progress related to that feature request? Will it be in 7 or rather in 8?

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Is there any plans to add a curvature graph to subd edges during the present version?

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We are still waiting for gaussian, draft angle and radius analisys.


Hello SubD team,
Is there any development on ‘Curvature Graph’ and ‘Curvature Analysis for SubD’?
@wim @stevebaer @theoutside @BrianJ

Not that I know of, sorry

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Dear McNeel Development Team,

It has come to our collective attention that this essential missing functionality has been ‘on the pile’ for over two years. In name of all of us modeling in SubD for production I please ask you to kindly consider prioritizing this over more esoteric sorcery tools.

Best Regards,

Your customers who are privileged to design and model for a living with your wonderful software.


Dear Steve,

The lesson that I teach all my Rhino students is:" You are only as good as you can analyze the quality of your work. Otherwise, you may have beginner’s luck".
How can I apply this lesson to my own SubD modelling jobs?


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I haven’t been involved in this project and only replied because you directly mentioned me and seeing as it is the week between Christmas and New Years many of my coworkers are on vacation. We’ll need to check with the devs involved.

If you convert your SubD to a polysurface and run analysis tools on the brep, do you get the visual feedback that you are looking for? If so, we could employ this technique in the background when running analysis on SubD.


Dear Steve,

Thank you for taking the time to reply in your vacation. Especially since you are no SubD developer, I really appreciate that.

You have a clever idea to convert to Nurbs in the background. However, as I use these analysis tools on the fly during fine-fairing, I need a quick respons and I am a little afraid of a delay.
I checked my model and the Surface Curvature analysis (Gaussian and Min.Radius) is useful, however the curvature graph isn’t useful at all as each Nurbs patch can have different UV orientation and that makes it impossible to review the curvature continuity in one direction along the whole object.

Interesting; @pierrec do you think it would be possible to improve consistency with UV orientation for these patches?

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how about you click on a curve (line projected or pull to the surface) and analyze surface curvature along this guide curve for inspection?

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What if in the background we could have many cross-sections curves projected to subd surfaces automatically to check their curvature graph. It would be much faster than converting subd to smooth polygon mesh only to check edges curvature. Maybe as input makes an optional curve line to get the custom direction of those sections if axes X,Y,Z as directions would be not enough.

Checking polygons on the mesh is bad because it depends on polygon flow. So if polygon flow is different from the shape you won`t be able to check the curvature graph of the actual shape. That’s why I think that projected lines would be a better idea IMHO.

Or maybe it would be possible to do it in both ways and let users choose which is better for their case. I`m only thinking loudly.

One I know for sure. Subd needs checking curvature graph and other surface analysis.

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@Gerard I don’t see that in my example files and I know that ToNURBS tries to keeps the orientations consistent. Can you send me your file so I can take a look please? Either in this forum or using Rhino - Upload to Support with my email ( as recipient.


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Hi Juan,
Yes, other ways to be able to investigate curvature are very appreciated here.
Most importantis that it works in real time during pulling and pushing control points so it gives me instant feedback.

Thank you for your input Marcin,
It is time that surface quality analysis tools for both Nurbs and SubD are re-evaluated and improved.

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