# Perfect Circle

Hey there,

How do I create an exact circular plane using subd?

Hi Lewis -

You canâ€™t. For exact circulars you need to use NURBS.
-wim

But if you use enough control points , you can get the deviation from a true circle to be so small, that even the center osnap will recognize it as a circle - hereâ€™s a triangle fan with 12 segments. Visually you will not be able to tell the deviation, but itâ€™s there - in this case itâ€™s 0.0105mm on a Ă¸100mm circle.

-Jakob

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Or at least I could have sworn that was the case, but itâ€™s not. Sorry for the noise!
-Jakob

This is an example with Grasshopper, you can create subd shape closer to circle but it is not a perfect circle.

subd circle.gh (12.5 KB)

@wim
it would be nice to have some info about the deviation for both

• deformable arcs / circles
• subD-Cylinders / spheres â€¦

it would be nice to have the info in the commandline, after starting the command (for current values) or after changing the options
(deformable: degree, Number of CVs)
(sub-D â€śarround facesâ€ť)

for example I imagine entering Degree 5 and 10 CVs for a deformable circle in a document with 0.001 units tolerance, a feedback would be great: maximum diameter within document-tolerance: 500mm.
the inverse info or an adaptive CV-Count would be great as wellâ€¦
(providing the minimum number of CVs / faces to stay within tolerance)

Hi Jakob - there is a setting for Center osnap locating centers of approximate circles - (Options > Modeling aids) that may effect what happens here, I have not tested on SubDs.

-Pascal

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Are there plans to add weights to subds?

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@oberbichler This would be excellent!