//输入：一个椭球参数与一个点的某些值;
//输出：该个点的另一些值;
public static void BL2xy(EarthPara earth, SpacePoint pt)
{
double B = pt.B;
double N = earth.N(B);
double t = earth.t(B);
double eta = Math.Sqrt(earth.Eta2(B));
//double Y0 = 500000.0;//Y方向的平移量;
double[] coef = new double[6];
CoefCalculator(earth, coef);
double meridianX = coef[0] * B + coef[1] * Math.Sin(2 * B) + coef[2] * Math.Sin(4 * B) +
coef[3] * Math.Sin(6 * B) + coef[4] * Math.Sin(8 * B) + coef[5] * Math.Sin(10 * B); //求子午线弧长;
double dl = pt.L - earth.L0 * Math.PI / 180; //经差;
double[] an = new double[7];
an[0] = meridianX;
an[1] = N * Math.Cos(B);
an[2] = N * t * Math.Pow(Math.Cos(B), 2) / 2.0;
an[3] = N * (1 - t * t + eta * eta) * Math.Pow(Math.Cos(B), 3) / 6.0;
an[4] = N * t * (5 - t * t + 9 * eta * eta + 4 * Math.Pow(eta, 4)) * Math.Pow(Math.Cos(B), 4) / 24.0;
an[5] = N * (5 - 18 * t * t + Math.Pow(t, 4) + 14 * eta * eta - 58 * Math.Pow(eta, 2) * Math.Pow(t, 2)) * Math.Pow(Math.Cos(B), 5) / 120.0;
an[6] = N * t * (61 - 58 * t * t + Math.Pow(t, 4) + 270 * eta * eta - 330 * Math.Pow(eta, 2) * Math.Pow(t, 2)) * Math.Pow(Math.Cos(B), 6) / 720.0;
pt.x = an[0] + an[2] * dl * dl + an[4] * Math.Pow(dl, 4) + an[6] * Math.Pow(dl, 6);
pt.y = an[1] * dl + an[3] * Math.Pow(dl, 3) + an[5] * Math.Pow(dl, 5);
}
public static void xy2BL(EarthPara earth, SpacePoint pt)
{
double[] coef = new double[6];
CoefCalculator(earth, coef);
double addNum = 0;
double X = pt.x + addNum;
double y = pt.y + addNum;
double B0 = X / coef[0];
double delta = coef[1] * Math.Sin(2 * B0) + coef[2] * Math.Sin(4 * B0) +
coef[3] * Math.Sin(6 * B0) + coef[4] * Math.Sin(8 * B0) + coef[5] * Math.Sin(10 * B0);
double Bf = (X - delta) / coef[0];
if (Math.Abs(Bf - B0) > 1.0e-8)
{
do
{
B0 = Bf;
delta = coef[1] * Math.Sin(2 * B0) + coef[2] * Math.Sin(4 * B0) +
coef[3] * Math.Sin(6 * B0) + coef[4] * Math.Sin(8 * B0) + coef[5] * Math.Sin(10 * B0);
Bf = (X - delta) / coef[0];
} while (Math.Abs(Bf - B0) > 1.0e-8);
}
//求解b的系数;
double Nf = earth.N(Bf);
//double Wf = ell.W(Bf);
double Mf = earth.M(Bf);
double tf = earth.t(Bf);
double etaf = Math.Sqrt(earth.Eta2(Bf));
double[] bn = new double[7];
bn[0] = Bf;
bn[1] = 1.0 / (Nf * Math.Cos(Bf));
bn[2] = -tf / (2 * Mf * Nf);
bn[3] = -(1 + 2 * tf * tf + etaf * etaf) * bn[1] / 6.0 / Nf / Nf;
bn[4] = -(5 + 3 * tf * tf + etaf * etaf - 9 * tf * tf * etaf * etaf) * bn[2] / 12.0 / Nf / Nf;
bn[5] = -(5 + 28 * tf * tf + 24 * Math.Pow(tf, 4) + 6 * etaf * etaf + 8 * tf * tf * etaf * etaf) * bn[1] / 120.0 / Math.Pow(Nf, 4);
bn[6] = (61 + 90 * tf * tf + 45 * Math.Pow(tf, 4)) * bn[2] / 360.0 / Math.Pow(Nf, 4);
double B = bn[0] + bn[2] * y * y + bn[4] * Math.Pow(y, 4) + bn[6] * Math.Pow(y, 6);
double dl = bn[1] * y + bn[3] * Math.Pow(y, 3) + bn[5] * Math.Pow(y, 5);
double L = earth.L0 * Math.PI / 180 + dl;
pt.B = B;
pt.L = L;
}
