Circular guide lines

I may be the only person who wants this, but…

I often need to find a point by triangulation. The traditional way to do that is to draw intersecting circles. You can then select the intersecting points. At present, I use ordinary circles to do that, but that means I have to laboriously erase them afterwards, usually in segments. A circular guide line would avoid all that (I have a keyboard shortcut that allows me to erase all guide lines at a stroke).

Maybe others have clever ways of doing this better than me.

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Maybe draw the circle in a group so you can delete faster ?

Yes I could do that but it is another set of keystrokes (not many, I accept).

I suspect there are other uses for circular guides other than triangulation, hence the feature request.

The request has been made before so maybe one day we’ll see them

Instead of making the circle a group, make it a component. Benefits:

Set the component origin at the center of the circle to make accurate insertion easy.
Save it for future use.
When you’re finished with the circles in your model, go to the In Model components library, right click on the circle component, choose Select Instances, hit Delete.

Also be aware that because they are really collections of edge segments, SketchUp’s circles don’t necessarily intersect at an accurate point.

It would be really great if SketchUp added some more capabilities to circles. Much more power should be possible, since the ArcCurve associated with the segments captures the original center, radius, and normal vector.


I’m in for true circles as guide circles. This wouldn’t interfere too much with SketchUp’s philosophy with segmented arcs and circles for real geometry, thus keeping the types of basic entities limited for the inferencing engine. (think of extruded segmented circles versus real cylindrical shapes)

If however you can get away with intersecting segmented guide arcs and circles in your workflow, this may be of help:

  • draw the desired arcs and/or circles, one at the time.
    (- if wanted, use ‘Find Center’ in the right click context menu).
  • per acr/circle entity right click on it and select ‘Convert to Construction Line’ in the context menu (see *).

‘Convert to Construction Line’ could even be assigned to a new shortcut key to speed up the process. (Edit/Item/Conver to Construction Line > to key)

Now all intersecting guide ‘circles’ and arcs’ will also be deleted as easily as straight guides.

(*) ‘Convert to Construction Lines’ should be downloaded as a plugin to see the command in the context menu.

You’re not the only one. I’ve been thinking about circular guidelines for a long time now. But since there are no true circles in SketchUp, they’d somehow have to be constructed from segments and most importantly - kept intact, meaning that they must not be “explodable” like the normal Circle and Polygon tools.
Also, if they are constructed from segments, the number must be synced with the Circle Tool to avoid tracing inconvenience. Just thoughts, of course but hopefully we’ll get something one day.

Exactly what I was also thinking ! There is no need to dumb down guide circles into a special collection of edge segments. And it would defeat the purpose that the OP and e1 else needs. True circle-circle and cirlce-line intersections, as well as true tangent points between guide circles and guide lines.

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That’s a worry. How can you triangulate accurately with such a limitation? I know you can change the number of segments in a circle, but that seems like a somewhat crude workaround rather than a solution.

I couldn’t find an existing extension that puts a cpoint at the intersection(s) of two circles, so unless somebody points one out I will create one.

Great. Will you post here when you have done it (not sure how much work is involved)?

The math/geometry part is done. I am adding validity checks and then need to wrap it as a Tool and Extension. Maybe later today or tomorrow.

Here is a beta version for people to test. I think it is solid, but use at your own risk: I cannot take responsibility if it damages your model! Please let me know if it works or if you find issues.

It is not packaged as an extension or have a toolbar yet, it just adds an item to the Tools menu. You can install it by downloading the attached rbz and then using Preferences->Extensions->Install Extension (do not put the rbz directly into your plugins folder, the Preferences item will take care of that for you).

When you activate this tool, it will prompt you to select two circles and will then place guide points at the intersections of the selected circles. The circles may be in any orientation in 3D, but must be coplanar. It will also work for circular arcs, finding the intersections of the full circles of which the arcs are portions, even if the rest of the circle hasn’t been drawn. It uses the full mathematical geometry of real circles, not SketchUp’s segmented representation, so the guides will usually lie slightly off SketchUp’s rendition of the circle.

Feedback welcome.

SB_intersect_circles.rbz (2.3 KB)

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have you done a gif yet?


Not yet, just flang a quickie out there to try the idea.

Here’s a brief gif. I created a rectangle at an intentionally skewed orientation. I drew two circles on the rectangle using 8 sides just to emphasize how this deals with SketchUp’s representation. I then drew circumscribing circles around the octagons using 128 segments. In the gif you can see several things:

  • the Tool recognizes the edges of the octagons as belonging to an ArcCurve portion of a circle
  • the guides are indeed placed very close to where the 128 segment circles cross, though the guides are exact and the crossings are affected by segmentation even at this scale.

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looking useful…


Well, how’s about that, then? You ask for an improvement and it shall be given…

I will defo be trying this out!

… and later tangent-circle and edge-circle intersects ?

Hmm… polygon-circle intersects ?

Hi folks.

See this SU file for ideas. It is a bit tedious but it works.

Triangle from 3 sides.skp (125.8 KB)

Here’s using my tool and ordinary 24-segment circles - no tweaking or adjusting, just drew it.