线段余弦角+凸包算法

        ///
        /// 根据余弦定理求两个线段夹角
        ///
        /// 端点
        /// start点
        /// end点
        ///
        double Angle(PointF o, PointF s, PointF e)
        {
            double cosfi = 0, fi = 0, norm = 0;
            double dsx = s.X - o.X;
            double dsy = s.Y - o.Y;
            double dex = e.X - o.X;
            double dey = e.Y - o.Y;
            cosfi = dsx * dex + dsy * dey;
            norm = (dsx * dsx + dsy * dsy) * (dex * dex + dey * dey);
            cosfi /= Math.Sqrt(norm);
            if (cosfi >= 1.0) return 0;
            if (cosfi <= -1.0) return Math.PI;
            fi = Math.Acos(cosfi);
            if (180 * fi / Math.PI < 180)
            {
                return 180 * fi / Math.PI;
            }
            else
            {
                return 360 - 180 * fi / Math.PI;
            }
        }

        /// <summary>
        /// 凸包算法
        /// </summary>
        /// <param name="_list"></param>
        /// <returns></returns>
        private List<TuLine> BruteForceTu(List<Info> _list)
        {

            //记录极点对
            List<TuLine> role = new List<TuLine>();

            //遍历
            for (int i = 0; i < _list.Count - 1; i++)
            {

                for (int j = i + 1; j < _list.Count; j++)
                {

                    double a = _list[j].Y - _list[i].Y;
                    double b = _list[i].X - _list[j].X;
                    double c = _list[i].X * _list[j].Y - _list[i].Y * _list[j].X;

                    int count = 0;
                    //将所有点代入方程
                    for (int k = 0; k < _list.Count; k++)
                    {

                        double result = a * _list[k].X + b * _list[k].Y - c;
                        if (result > 0)
                        {

                            count++;

                        }
                        else if (result < 0)
                        {

                            count--;

                        }

                    }
                    //是极点，则将连线记录下来
                    if (Math.Abs(count) == _list.Count - 2)
                    {

                        TuLine line = new TuLine();
                        IPoint pi = new PointClass();
                        pi.X = _list[i].X;
                        pi.Y = _list[i].Y;
                        line.Begin = pi;

                        IPoint Pj = new PointClass();
                        Pj.X = _list[j].X;
                        Pj.Y = _list[j].Y;
                        line.End = Pj;
                        role.Add(line);
                    }

                }

            }
            return role;
        }