title: DXF generation using ezdxf: polyline containing spline fit points
body: <p>I am developing a program, and one of the requirements is to take DXF as input. The input is limited to 2D case only. The program itself is in C++/Qt, but to test it I need some sample DXF input. The spline import is already implemented, the next step is polyline <em>with spline fit points or control points</em> added. I decided to use Python/ezdxf to generate such polyline, as I don't have Autocad.</p>
  <p>My first approach was to create a spline from fit points utilizing <code>add_spline_control_frame</code>, then convert it to polyline. The problem is there turned out to be no conversion from spline to polyline (although I think I saw it in the docs, but cannot find it anymore).</p>
  <p>The current approach is to make polyline by <code>add_polyline2d(points)</code>, making each point to be with DXF flag field equal <code>8</code> (spline vertex created by spline-fitting). The problem is points need to be of type <code>DXFVertex</code> (docs state <code>Vertex</code>, but it is absent), and that type is private for ezdxf.</p>
  <p>Please share your approaches either to the problems I've faced with ezdxf, or to the initial problem.</p>
  <p>P.S. I tried to use LibreCAD to generate such a polyline, but it's hardly possible to make a closed polyline from spline fit points there.</p>