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);
          //}
      }
     

   

  }

圆弧转多段线方法如下：

 

  public void XX()
  {
      List<Curve> ents = Z.db.SelectEntities<Curve>();
      
      foreach (var item in ents)
      {
          if (item is Arc arc)
          {
              double ang = 0;
              if (arc.StartAngle > arc.EndAngle)
              {
                  double endangle;
                  endangle = arc.EndAngle + 2 * Math.PI;
                  ang = endangle - arc.StartAngle;
              }
              else 
              {
                  ang = arc.EndAngle - arc.StartAngle;
              }
              //Debugger.Break();
              ang = ang/4; 
              double td = Math.Tan(ang);
              // arc.Spline;
             Polyline pl = new Polyline();
             // if arc.StartAngle
              pl.AddVertexAt(0,new Point2d(item.StartPoint.X,item.StartPoint.Y),td,0,0);
              pl.AddVertexAt(1,new Point2d(item.EndPoint.X, item.EndPoint.Y),0, 0, 0);
              pl.ColorIndex = 1;
              Z.db.AddEntityToModeSpace(pl);
          }
         
      }
      foreach (var item in ents)
      {
          if (item is Arc arc1)
          {
              Z.db.Erase(arc1);
          }
      }
  }