How to make this lines as smooth curved line?

This is scan by template machine and the lines connected each other by a short straight lines.
Does anyone who knows how to make this line as smoother curved line as natural?
please help me !!!

Arch Benchtop.skp (102.3 KB)

Curvizard plugin. If you plan to make a face with this you may want to first be sure it’s coplanar. I would do that with Vertex tools but if you don’t have that, someone may be able to explain another way.

In SketchUp, you can use the Fredo6: Bezier Spline v2.1a plugin:

Arch Benchtop8.skp (25.7 KB)

For a more accurate drawing, you can use DraftSight (CAD).
You only need the following commands:

  • spline
  • l - line
  • a - arc
  • tr - trim
    plus ESnaps on / off

Draw over it with the Fredo Catmull spline tool.