任意多点按某一方向排序

    List<PointF> SortPoints(PointF[] points)
    {
      List<PointF> result = new List<PointF>();
      PointF center = GetGravityPoint(points.ToList());
      PointF x = new PointF(center.X+1, center.Y);
      PointF OX = new PointF(1,0);
      double OX_len = 1;

      List<double>  angle = new List<double>();

      foreach (PointF point in points)
      {
        PointF tmpO = new PointF(point.X-center.X,point.Y-center.Y);
        double tmp_len = Math.Sqrt((point.X - center.X)*(point.X - center.X)+(point.Y - center.Y)*(point.Y - center.Y));
        angle.Add(Math.Asin((tmpO.X)/tmp_len));
      }
      List<double>  tmpAngle = new List<double>(angle);
      tmpAngle.Sort();
      List<double> doubles = new List<double>();
      for(int i = 0;i< tmpAngle.Count;i++)
      {
        double tmp = tmpAngle[i];
        int v = angle.FindIndex(item => item.Equals(tmp));
        result.Add(points[v]);
      }     

      return result;
    }
    private PointF GetGravityPoint(List<PointF> lstPol)
    {

      double n, i;
      double x1, y1, x2, y2, x3, y3;
      double sum_x = 0, sum_y = 0, sum_s = 0;

      x1 = lstPol[0].X;
      y1 = lstPol[0].Y;
      x2 = lstPol[1].X;
      y2 = lstPol[1].Y;

      n = lstPol.Count;
      int k = 2;
      for (i = 1; i <= n - 2; i++)
      {
        x3 = lstPol[k].X;
        y3 = lstPol[k].Y;
        double s = ((x2 - x1) * (y3 - y1) - (x3 - x1) * (y2 - y1)) / 2.0;
        sum_x += (x1 + x2 + x3) * s;
        sum_y += (y1 + y2 + y3) * s;
        sum_s += s;
        x2 = x3;
        y2 = y3;
        k++;
      }
      PointF center = PointF.Empty;
      center.X = Convert.ToSingle(sum_x / sum_s / 3.0);
      center.Y = Convert.ToSingle(sum_y / sum_s / 3.0);
      //MessageBox.Show("("+center.X.ToString()+","+center.Y.ToString()+")");
      return center;
    }