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