TrueTangents v1.2
功能1：通过辅助点和已知圆或圆弧，添加点到圆的正切辅助线。
功能2：通过已知的两个圆或圆弧，添加之间的正切线。
This Ruby provides two functions - 'truetangents' and 'commontangents' - it has plugin-menu items or type the names to run it from the Ruby Console. It's written to work on a selection BUT could be reconstructed as a cline method if thought useful... truetangents
Select an arc/circle and a cpoint (aka guide-point)
Run truetangents
On errors - e.g. no arc selected or the cpoint is inside the circumference - there is a console message.
It then draws cpoints at the arc centre and tps, and clines on the two radii and tangents - it draws to the true tps - these might not be on the arc itself if it's lightly segmented - now you can rotate, entity-info increase segments or reconstruct the arc as desired so it passes through a tp... commontangents
Select an arc/circle
Select a second arc/circle
Run commontangents
On errors - e.g. 2 arcs not selected or a circle within another circle can have no common tangents - there is a console message.
It then draws cpoints at the arc centres and tps, and clines on the four radii and two/four tangents - it draws to the true tps - these might not be on the arc itself if it's lightly segmented - now you can rotate, entity-info increase segments or reconstruct the arc as desired so it passes through a tp... Different forms of common tangent are produced if the arcs are separated by clear space or intersect (4 or 2 nr)...
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