Intersection circle problem

I have some question about circles.
I want to draw two intersecting circles and than draw the line (chord) between intersection points.
Than I want to export that to acad (dxf or dwg), and open that in AutoCad.
Please let me know how to do that properly? Where should I start and finish drawing the chord line?
As I noticed there are 3 active points appearing when I try to find the proper point by mouse. Please see the attachement. This it the drawing and the second drawing is the magnification of the crossing place. Where is the exact plase of crossing two circles???


What version of SketchUp are you using? That will affect the answer to your question.

Please complete your profile.

It is SU2019

Ok. TIG’s Tangent Tools contains a tool called True Intersections. It’ll give you the location of the true chord between the circles among other things.

The centers are also identified so if you want you can use the Arc tool to replace the two overlapping circles with arcs that meet at the true ends of the chord.

Thanks for completing your profile info. That helps us help you.

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It is a bit of a pain when working with much more complicated models.

And how to indicate the simple line and circle true intersecting point and how to catch it ?
I want to start new line there and when suggestions appears during I hover the mouse over, I can’t snap the new line to this point (gray point).
Is the method to snap and start the lines in true intersection points?
Is there some method to toggle the active point from green to nearest gray point (true intersection)?


The unhappy truth about SketchUp is that inferencing doesn’t recognize true circles or arcs, only the line segments. Correcting that would probably require a rewrite of the application from the ground up.

Unfortunately, because SketchUp represents circles and circular arcs using collections of straight edges, there are unavoidable issues when edges, arcs, or circles intersect circles or arcs. Except if the intersection is at vertices of circles, there is a gap between the true circle and SketchUp’s representation. That means that SketchUp’s notion of the intersection can’t in general lie on the true circle and conversely the true intersection can’t in general lie on SketchUp’s representation.

Extensions such as TIG’s True Tangents or my Circle Intersect can show you where the mathematically correct intersection points would be, but they can’t do anything about this fundamental limitation within SketchUp.

If you export or import from a format that supports true circles, you can already see the consequences: an edge that is supposed to stop at its intersection with a true circle will either pass through or stop short.

The changes required to eliminate these issues are so fundamental that SketchUp’s geometry engine would indeed have to be reconceived from the ground up.

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A quite acceptable middle way would be to introduce long awaited for circular guides.

That would let you find and draw edges to true intersection points, but would do nothing to improve the situation when you want both the circle and the edge (or two circles) since as true circles the guides wouldn’t match SketchUp’s circles.

Regardless, because there are extensions such as TIG’s and mine that can already show you where true circles intersections lie, I would be very surprised if the developers gave this any priority.

You can also use more segments per circle to increase the precision.

Click in sequence on the Scenes tabs of this SU file.

Circle intersections.skp (217.8 KB)

I wonder. If it can quickly inference the center point of an arc, it has the info to find the true arc between segments by way of the radius and a variable angle, both of which it does quite well.

True. but I was thinking ahead: both intersections give you the opportunity to draw four arcs between both true intersections, using both circle centers, to replace these circles. The segmented circles wouldn’t change a thing.