public CircularArc3d ArcToNative(Arc arc)
{
var _arc = new CircularArc3d(PointToNative(arc.startPoint), PointToNative(arc.midPoint), PointToNative(arc.endPoint));
_arc.SetAxes(VectorToNative(arc.plane.normal), VectorToNative(arc.plane.xdir));
_arc.SetAngles((double)arc.startAngle, (double)arc.endAngle);
return(_arc);
}