CAD中圆可转为带有凸度的多段线以方便后期数据计算、处理，效果如下：

白色为圆，红色为转换后的多段线（为区分，已手工偏移多段线）

  public static  void XX(){var curves = Z.db.SelectEntities<Entity>();foreach (var item in curves){if (item is Circle){Circle temp = (Circle)item;Point3d pt = temp.Center;double leftx = pt.X - temp.Radius;double rightx = pt.X + temp.Radius;double topx = pt.X;double bottomx = pt.X;double lefty = pt.Y;double righty = pt.Y;double topy = pt.Y + temp.Radius;double bottomy = pt.Y - temp.Radius;Point2d left = new Point2d(leftx, lefty);Point2d right = new Point2d(rightx, righty);Point2d top = new Point2d(topx, topy);Point2d bottom = new Point2d(bottomx, bottomy);Polyline pl = new Polyline();pl.AddVertexAt(0, bottom, 1, 0, 0);pl.AddVertexAt(1, top, 1, 0, 0);pl.AddVertexAt(2, bottom, 0, 0, 0);pl.ColorIndex = 1;Z.db.AddEntityToModeSpace(pl);pl.Highlight();// Debugger.Break();}//else//{//    Z.db.Erase(item);//}}}