/// <summary>
        /// 求直線外一點到該直線的投影點
        /// </summary>
        /// <param name="pLine">線上任一點</param>
        /// <param name="k">直線斜率</param>
        /// <param name="pOut">線外指定點</param>
        /// <param name="pProject">投影點</param>
        protected void GetProjectivePoint(PointF pLine, double k, PointF pOut, ref PointF pProject)
        {
            if (k == 0) //垂線斜率不存在情況
            {
                pProject.X = pOut.X;
                pProject.Y = pLine.Y;
            }
            else
            {
                pProject.X = (float)((k * pLine.X + pOut.X / k + pOut.Y - pLine.Y) / (1 / k + k));
                pProject.Y = (float)(-1 / k * (pProject.X - pOut.X) + pOut.Y);
            }
        }