Inspiring

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Is there a way to draw a perfect circle in illustrator CC?

Forum|Forum|6 years ago
April 18, 2019
6 replies
15299 views

Not sure if this is a recent bug or has always been there, but I cannot seem to draw a perfect circle using the ellipsis tool.

Shift > click + drag (doesn't work)

clicking artboard and setting width and height to equal values (doesn't work)

Found the following feature request that explains the issue a bit more.

The circles in Illustrator are flawed and here's why. – Adobe Illustrator Feedback

Is there a way to use the circle equation to create a circle without infinite anchor points?

(x−h)² + (y−k)² = r²

Or perhaps a way to manually draw a circle, although seemingly unlikely?

Re: Drawing a perfect circle

Or are other importable files like SVG capable of perfect circles that could be imported into illustrator?

</svg>

I tried importing this SVG into illustrator, but it wasn't successful. Not sure if illustrator is converting the SVG or my method of import was incorrect.

Note: I have no idea if SVG files / definitions are capable of perfect circles, but if they are, then the above definition I believe would be a perfect circle.

This topic has been closed for replies.

Correct answer Doug A Roberts

I noticed it as I was building an asset and I know a couple strategies to circumvent the issue. My hope in posting was that I could find a way to not have to circumvent the issue.

Based on what I can tell, Illustrator "circle" polygons are likely octograms or octagons with curves, while a true circle polygon is a monogon.

Perfect circles cannot be created with bezier curves. No software that draws in bezier curves can draw a perfect circle.

Jeff Witchel, ACI

Community Expert

You can also make what looks like a Stroked circle by rotating a 2 pt. X 2 pt. rectangle around a center point that's offset from the rectangle (the radius of the circle).

See screenshot attached.

Now that I think about it, either of these Rotate solutions can be done with a Transform Effect and then saved as a Graphic Style to be easily repeated.

Jeff Witchel, ACI

Community Expert

Just curious, what kind of project is this that such extreme accuracy is so critical? I can't think of any end usage that anyone would even be able to see such microscopic differences.

And by they way, there is a way to draw a perfect circle in Illustrator. It's ridiculous, but it works.

Draw a line segment and add a 2pt. Stroke.
Option (Alt)-Click on one end of the Stroked path with the Rotate tool (R).
Enter .5° for Angle and press Copy.
Press Command+D (Control+D [Windows]) as many times as needed to make enough copies to complete your "perfect" circle.

I said that it's ridiculous, but it does work. At any angle this is turned it's exactly the same radius. I got the idea from Sandee's Flatness post.

See screenshot below.

Kurt Gold

Community Expert

It may sound a bit nitpicking, Jeff, but this isn't a real "perfect" circle either. It's another approximation.

It is very close and the deviations are pretty marginal, but they are still there, although Illustrator's Transform palette may not display them due to rounding differences.

Jeff Witchel, ACI

Community Expert

Noted!

Thanks Kurt!

T

Test Screen Name

Legend

Ironically, if a CAD app prints to a PostScript printer, or writes PDF, your arcs will turn to beziers...

Sandee Cohen

Legend

Out of curiosity, how did you discover this? I had to zoom in 34000% to see the difference of two identical circles where one has been rotated 6% from the other. In my example the difference was .0002 mm. As they used to say in the Army, "close enough for government work."

Doug A Roberts

Community Expert

Sandee, I think it's most easily observed by making a circle of specific dimensions and watching them change slightly as you rotate it.

Can SVGs draw real circles, Kurt? The OP suggests they can. If that's the case, perhaps Inkscape can.

Kurt Gold

Community Expert

Does SVG support real circles? Well, Doug, I don't know. But I also think that in (my) real world there are no real circles at all. Moreover, I doubt that real circles even exist. Real circles are imagination.

Have you ever seen a real circle? If that applies, I'd be greatful if you could show me where it is.

Jacob Bugge

Community Expert

norinam,

A Bezier circle created with 4 Anchor Points created to have the exact diameter at every 45 degrees, in other words vertical and horizontal and midway in between (as Illy does it, and she has made a good choice), is inherently bulging in between (in between).

Circumference ratio compared with true circle 1.000012175, deviation 0.000012175 or about 12 in a million.

Bulging rate (relative radius/diameter) at 22.5 degrees compared with true circle 1.0002617, deviation 0.0002617 or about 262 in a million.

As you have seen already, it can be seen; and sometimes adjustments are needed to counter the inaccuracy, as in this case from some days ago:

Concentric circles, but not quite.

Kurt Gold

Community Expert

Wasn't there a circle thread one or about two decades ago? With some suggestions, but no real circle?

What is a real circle (apart from a mathematical point of view)?

Jacob Bugge

Community Expert

Are you thinking of this one, Kurt, The Circle Thread?

Illustrator Windows hints

Monika Gause

Community Expert

Can you please post a screenshot of the issue?

norinamAuthor

Inspiring

The following image shows the edge of two identical 400 x 400 px "circles".

The orange circle was rotated 6° and the edge zoomed in at 64000%.

Both circles were selected so you can see the faint blue vector line for each.

Monika Gause

Community Expert

Importing an SVG won't solve your issue, because Illustrator converts it to its own way of doing things.

On top of that there might be issues with the GPU rendering - you could try if the CPU improves it.

And then: if you need this level of precision, probably you'll need to use CAD software.

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