大地坐标系(wgs84)转UTM
飞机上的pos和各种GPS设备用的基本上都是用经纬度保存位置信息。而我们平常计算长度和面积什么的都是米、平方米什么的。就必然涉及到坐标系的转换。众多坐标系里，我觉得utm比较适合公制单位的计算。主要是各种商业GIS软件支持的都比较好。
转换的工具和库很多，我个人比较喜欢GDAL。但如果只是转个坐标，再高一大堆DLL什么的就很麻烦。于是就开始找资料。竟然没找到现成的c#代码。。。
干脆自己根据一个网站上的js写了一个。
class Program
{
static void Main(string[] args)
{
double[] utm = LatLonToUTM(30.65156708, 103.6880587);
}
static double pi = Math.PI;
static double sm_a = 6378137.0;
static double sm_b = 6356752.314;
//static double sm_EccSquared = 6.69437999013e-03;
static double UTMScaleFactor = 0.9996;
//得到的结果是：x坐标，y坐标，区域编号
public static double[] LatLonToUTM (double lat, double lon)
{
double zone = Math.Floor((lon + 180.0) / 6) + 1;
double cm = UTMCentralMeridian(zone);
double[] xy = new double[2];
MapLatLonToXY(lat / 180.0 * pi, lon / 180 * pi, cm, out xy);
/* Adjust easting and northing for UTM system. */
xy[0] = xy[0] * UTMScaleFactor + 500000.0;
xy[1] = xy[1] * UTMScaleFactor;
if (xy[1] < 0.0)
{
xy[1] = xy[1] + 10000000.0;
}
return new double[] { xy[0], xy[1], zone };
}
public static double UTMCentralMeridian (double zone)
{
double cmeridian;
double deg = -183.0 + (zone * 6.0);
cmeridian = deg / 180.0 * pi;
return cmeridian;
}
internal static void MapLatLonToXY (double phi, double lambda, double lambda0, out double[] xy)
{
double N, nu2, ep2, t, t2, l;
double l3coef, l4coef, l5coef, l6coef, l7coef, l8coef;
double tmp;
/* Precalculate ep2 */
ep2 = (Math.Pow(sm_a, 2.0) - Math.Pow(sm_b, 2.0)) / Math.Pow(sm_b, 2.0);
/* Precalculate nu2 */
nu2 = ep2 * Math.Pow(Math.Cos(phi), 2.0);
/* Precalculate N */
N = Math.Pow(sm_a, 2.0) / (sm_b * Math.Sqrt(1 + nu2));
/* Precalculate t */
t = Math.Tan (phi);
t2 = t * t;
tmp = (t2 * t2 * t2) - Math.Pow (t, 6.0);
/* Precalculate l */
l = lambda - lambda0;
/* Precalculate coefficients for l**n in the equations below
so a normal human being can read the expressions for easting
and northing
-- l**1 and l**2 have coefficients of 1.0 */
l3coef = 1.0 - t2 + nu2;
l4coef = 5.0 - t2 + 9 * nu2 + 4.0 * (nu2 * nu2);
l5coef = 5.0 - 18.0 * t2 + (t2 * t2) + 14.0 * nu2
- 58.0 * t2 * nu2;
l6coef = 61.0 - 58.0 * t2 + (t2 * t2) + 270.0 * nu2
- 330.0 * t2 * nu2;
l7coef = 61.0 - 479.0 * t2 + 179.0 * (t2 * t2) - (t2 * t2 * t2);
l8coef = 1385.0 - 3111.0 * t2 + 543.0 * (t2 * t2) - (t2 * t2 * t2);
/* Calculate easting (x) */
xy = new double[2];
xy[0] = N * Math.Cos (phi) * l
+ (N / 6.0 * Math.Pow (Math.Cos (phi), 3.0) * l3coef * Math.Pow (l, 3.0))
+ (N / 120.0 * Math.Pow(Math.Cos(phi), 5.0) * l5coef * Math.Pow(l, 5.0))
+ (N / 5040.0 * Math.Pow(Math.Cos(phi), 7.0) * l7coef * Math.Pow(l, 7.0));
/* Calculate northing (y) */
xy[1] = ArcLengthOfMeridian (phi)
+ (t / 2.0 * N * Math.Pow(Math.Cos(phi), 2.0) * Math.Pow(l, 2.0))
+ (t / 24.0 * N * Math.Pow(Math.Cos(phi), 4.0) * l4coef * Math.Pow(l, 4.0))
+ (t / 720.0 * N * Math.Pow(Math.Cos(phi), 6.0) * l6coef * Math.Pow(l, 6.0))
+ (t / 40320.0 * N * Math.Pow(Math.Cos(phi), 8.0) * l8coef * Math.Pow(l, 8.0));
return;
}
internal static double ArcLengthOfMeridian(double phi)
{
double alpha, beta, gamma, delta, epsilon, n;
double result;
/* Precalculate n */
n = (sm_a - sm_b) / (sm_a + sm_b);
/* Precalculate alpha */
alpha = ((sm_a + sm_b) / 2.0)
* (1.0 + (Math.Pow(n, 2.0) / 4.0) + (Math.Pow(n, 4.0) / 64.0));
/* Precalculate beta */
beta = (-3.0 * n / 2.0) + (9.0 * Math.Pow(n, 3.0) / 16.0)
+ (-3.0 * Math.Pow(n, 5.0) / 32.0);
/* Precalculate gamma */
gamma = (15.0 * Math.Pow(n, 2.0) / 16.0)
+ (-15.0 * Math.Pow(n, 4.0) / 32.0);
/* Precalculate delta */
delta = (-35.0 * Math.Pow(n, 3.0) / 48.0)
+ (105.0 * Math.Pow(n, 5.0) / 256.0);
/* Precalculate epsilon */
epsilon = (315.0 * Math.Pow(n, 4.0) / 512.0);
/* Now calculate the sum of the series and return */
result = alpha
* (phi + (beta * Math.Sin (2.0 * phi))
+ (gamma * Math.Sin(4.0 * phi))
+ (delta * Math.Sin(6.0 * phi))
+ (epsilon * Math.Sin(8.0 * phi)));
return result;
}
}