火星坐标转换为GPS坐标

     中国的地图和卫星图都存在一个偏移量，我们在Google Map上看到的坐标与实际的GPS坐标其实是有着一定范围的偏移的，而在Google Earth上看到的坐标与GPS坐标是完全一致的，也就是说，同一张地图图片，切换到Google Map和Google Earth模式下的地图实际是上不匹配的，为什么会有这个偏移这里就不作叙述了，那么当我们拿到地图上的座标以后，要怎样转成GPS坐标呢？

     在google中找到一段C的代码，主要是借助一组码表，加上一个计算公式而得到GPS坐标，我用C#翻译了一下，下面贴上代码：

 

 

double[] TableY = new double[660 * 450];
        bool InitTable = false;

        public Form1()
        {
            InitializeComponent();

            LoadText();
        }

        private int GetID(int I, int J)
        {
            return I + 660 * J;
        }

        private void LoadText()
        {
            using (StreamReader sr = new StreamReader("Mars2Wgs.txt"))
            {
                string s = sr.ReadToEnd();

                Match MP = Regex.Match(s, "(\\d+)");

                int i = 0;
                while (MP.Success)
                {
                    //MessageBox.Show(MP.Value);
                    if (i % 2 == 0)
                    {
                        TableX[i / 2] = Convert.ToDouble(MP.Value) / 100000.0;
                    }
                    else
                    {
                        TableY[(i - 1) / 2] = Convert.ToDouble(MP.Value) / 100000.0;
                    }
                    i++;
                    MP = MP.NextMatch();
                }
                InitTable = true;
                //MessageBox.Show((i / 2).ToString());
            }
        }

        /// <summary>
        /// x是117左右，y是31左右
        /// </summary>
        /// <param name="xMars"></param>
        /// <param name="yMars"></param>
        /// <param name="xWgs"></param>
        /// <param name="yWgs"></param>
        private void Parse(double xMars, double yMars, ref double xWgs, ref double yWgs)
        {
            int i, j, k;
            double x1, y1, x2, y2, x3, y3, x4, y4, xtry, ytry, dx, dy;
            double t, u;

            if (!InitTable)
                return;

            xtry = xMars;
            ytry = yMars;

            for (k = 0; k < 10; ++k)
            {
                // 只对中国国境内数据转换
                if (xtry < 72 || xtry > 137.9 || ytry < 10 || ytry > 54.9)
                {
                    return;
                }

                i = (int)((xtry - 72.0) * 10.0);
                j = (int)((ytry - 10.0) * 10.0);

                x1 = TableX[GetID(i, j)];
                y1 = TableY[GetID(i, j)];
                x2 = TableX[GetID(i + 1, j)];
                y2 = TableY[GetID(i + 1, j)];
                x3 = TableX[GetID(i + 1, j + 1)];
                y3 = TableY[GetID(i + 1, j + 1)];
                x4 = TableX[GetID(i, j + 1)];
                y4 = TableY[GetID(i, j + 1)];

                t = (xtry - 72.0 - 0.1 * i) * 10.0;
                u = (ytry - 10.0 - 0.1 * j) * 10.0;

                dx = (1.0 - t) * (1.0 - u) * x1 + t * (1.0 - u) * x2 + t * u * x3 + (1.0 - t) * u * x4 - xtry;
                dy = (1.0 - t) * (1.0 - u) * y1 + t * (1.0 - u) * y2 + t * u * y3 + (1.0 - t) * u * y4 - ytry;

                xtry = (xtry + xMars - dx) / 2.0;
                ytry = (ytry + yMars - dy) / 2.0;
            }

            xWgs = xtry;
            yWgs = ytry;

        }

        private void button1_Click(object sender, EventArgs e)
        {
            double x = Convert.ToDouble(txbX.Text);
            double y = Convert.ToDouble(txbY.Text);

            double xWgs = x;
            double yWgs = y;

            Parse(x, y, ref xWgs, ref yWgs);

            ltrResult.Text = "X:" + xWgs.ToString() + ",Y:" + yWgs.ToString();
        }

来源：http://www.cnblogs.com/ahhi/archive/2010/04/27/Wars2Wgs.html