Segmented circles/curves

When circles are drawn they appear segmented. How then, can where 2 circles intersect be accurately pin pointed if only segmented lines are showing? I think there is a way you ca reset the screen but have forgotten how? (Occaisonal user returning)

You can increase the number of segments and get a closer approximation of perfect, but they will never be perfect arcs and the intersection location may never be mathematically pin point perfect. I believe you can rotate a circle/arc so one of the apexes between the segments is oriented in a way to get something close to actual though. My understanding is the apexes represent the actual diameter.

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This plugin (Extension) might helps:

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or this one (shamelessly one of mine)


I use @slbaumgartner’s Circle Intersect frequently, it is very handy!

Thank you, but is that on Pro? Because I can’t find it in any of the Menus. I’m on Sketchup Free.

@2no Your profile indicates that you use SketchUp Pro 2018, which is a desktop native version of SketchUp (and which does support the installation of extensions, such as Circle Intersect). SketchUp Free is one of the web-based versions of SketchUp. The web-based versions to not support any extensions at the moment. I imagine that support for extensions will be added to the web-based versions in a year or two, but not yet. [Edited to correct a typo.]

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My Sketchup Pro expired so reverted to Free. Thanks. Such extesions should be a fundametal part of this as it is mad that you can’t verify exact points due to segmentation!

It isn’t ‘mad’ that you can’t. It’s just a manifestation of the way SketchUp was designed from its inception as an edge and face modeller, that generates surfaces from straight edges.

But if you can get round it due to extensions, why not include that as fudamental?

Only because the designers want to keep it simple, and mainly provide only the tools that almost everyone wants to use, I think.

Specialised things that most people don’t want or need aren’t added, so as to keep the overall interface as clean and simple as possible.

That seems to be the design philosophy, anyway.

For example, I’ve used Sketchup for over ten years for theatre set drawing and design, and detailed drawings, and for standalone woodworking. I’ve never needed to intersect circles precisely in over ten years of use.

You need it, there’s a plugin for it. I don’t need it, so it doesn’t get in my way, because I don’t have the plugin.

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Thank you. Does this work for SketchUp Free or ? I have only Free version. I’m not sure how to install it. I found Preferences but no “Install”. I used AutoCad years ago and find SketchUp quite easy though I think my brain stopped at 70 years old… it’s OK for you youngsters… Please do tell how I can install!

Please correct your forum profile. It says you are using 2018 Pro, not any variation of “Free”.

Only the desktop versions can install extensions; the web versions cannot. And, SketchUp Make 2017 was the last no-cost desktop version.

I’m over 70 myself.


If pro 2018 was a purchased license you should still be able to run it and it will run the plugins.

It can be disappointing, I’ll grant that. SketchUp is not a “traditional” Computer Aided Drafting/Drawing program. That’s perhaps good and bad. Native SketchUp lacks various features that would be very useful for mechanical design drawings, such as accurate circles and circular arcs, with associated features such as arc and line intersections. On the other hand, the somewhat minimal native drawing tools are relatively easy to learn and surprisingly powerful. Also, by intent, SketchUp’s built-in full programming language and API enables amazing features - beyond the native tools - to be provided by clever people around the world.

For the past seven or so years, I have been using SketchUp to make models of mechanical parts, where accuracy and precision are important to me. SketchUp’s approximations of arcs and circles has been a concern; I worry that a few years from now, I will regret choosing SketchUp for my long-term historical project because of curve approximations. Time will tell.

For now, I use @slbaumgartner’s Circle Intersect (and occasionally @TIG’s True Tangent) extension - with a native Desktop version of SketchUp - to ensure that arcs are represented as “reasonably” as possible. For example, I prefer that all segments of an arc are equal-length and that the first and last end-points of the arc are exactly the desired radius distance from the arc’s center point. Therefore, I don’t just cut a chord out of a circle wherever the desired straight edge happens to cross two of the circle’s segments. I’ll use the Circle Intersect extension with some temporary arcs and edges to determine the exact end points of the arc, then draw a clean arc between them.

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I’m nearing 79 myself!

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I’ll have to try this. Been looking for something that does this!

It would not have to be so disappointing at all if SketchUp had a native circular guide tool
Such a tool, very simple to use, would not clutter SketchUp’s interface and would not interfere with SketchUp’s philosophy to keep things simple.
A circular guide tool would help solving problems as mentioned by OP without extentions, perfect for the web versions that can’t cope with extentions.


Yes, this would be nice. I would vastly prefer it if SketchUp had actual mathematically precise continuous circle and circular arc entities. (I know that will never be added, but in an alternate universe…).