lib2geom

I was investigating if anyone had made a dedicated center & point on circle tool for inkscape,
and it looks like it might be available in an upcoming release.
http://inkscape.13.x6.nabble.com/Do-geometric-contructions-tool-general-Inkscape-UX-discussions-td4972941.html

During my investigation I found:
http://lib2geom.sourceforge.net/
http://inkscape.13.x6.nabble.com/2Geom-sync-status-td4973615.html

Even if you can't or won't use it, you might be able to learn something from it,
so I thought I would mention it.