C#下的GPS座标纠偏方法（也叫火星座标）

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？

我在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：

项目文件下载：Wars2Wgs.rar 

        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();

        }