# Tangent lines to curves

As we know that circles and arches are made of strait lines, I find difficult to connect a line tangent to a circle or arch.
Is there a way to overcome this challenge? Well, without increasing the number of segments forming the circle or arch.

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This is indeed problematic since SketchUpâ€™s polygonal representation of a circle or arc does not necessarily have any point where a tangent would touch the theoretical circle. The best answer may be TIGâ€™s plugin:

http://sketchucation.com/plugin/771-truetangents

My old http://sketchucation.com/pluginstore?pln=TrueTangents
Makes guides/points at true tangents, arc intersections etcâ€¦
You then redraw between thoseâ€¦

SU shows tangencies (with cyan inferencing for single-tangent or magenta inferencing for double-tangent). The tangent inferencing appears when you draw a curve tangent to an edge but not an edge tangent to a curve.

-Gully

Hi folks.

Decide where you want the tangency point. Then, draw a radius from the center of the curve to the periphery of the curve. If this point is between two endpoints, draw two edges from these points to the desired tangency point and then erase the previous edge between these two endpoints.

Then draw a perpendicular to this radius. It shall be tangent to the curve.

If you can post a skp file of your curve, it would be possible to see if this is feasible with it.

Just ideas.

Jean

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Thank you guys!!!
The problem is clear now using SketchUp.

jean,
1.- Would you please explain to me this part of your answer: â€¦"If this point is between two endpoints, draw two edges from these points to the desired tangency point and then erase the previous edge between these two endpoints."
2.- Another challenge that I would like to solve geometrically (not with SketchUp) is how to draw a tangent line when you have a circle and a point some distant outside the circle from where the tangent line starts.
Thank you.

Hereâ€™s a graphical solution: How to construct (draw) tangents to a circle through an external point - Math Open Reference

-Gully

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Point 2. - see my TrueTangentsâ€¦

Hi cb94030, hi folks.

Click in sequence on the scenes tabs of this SU file for ideas.

Tangent to a curve.skp (93.3 KB)

Jean

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Very informative post and dew-ly bookmarkedâ€¦Thanks All!! andâ€¦Peaceâ€¦

Gully, Jean,
THANKS A LOT!!! You guys made my day.
That was exactly what I needed. Actually as I like geometry, the page that you sent me Gully is like a candy for a kid.
Chris

After 4 years I need it again and I forgot about how to do it.
I came back to this thread and you guys Gully and Jean made my day one more time. Love you guys!!!