// longitude0, latitude0, parallel1, parallel2
public AlbersEqualAreaProjection(Dictionary <String, double> parameters)
: base(parameters)
{
double latitude0_rad = InputLatitude("latitude0");
double parallel1_rad = InputLatitude("parallel1");
double parallel2_rad = InputLatitude("parallel2");
double cos_parallel1 = Math.Cos(parallel1_rad);
double sin_parallel1 = Math.Sin(parallel1_rad);
_n2 = sin_parallel1 + Math.Sin(parallel2_rad);
if (Math.Abs(_n2) <= MathX.Tolerance)
{
throw new ArgumentOutOfRangeException();
}
_n = _n2 / 2;
_n_half = _n2 / 4;
_inv_n2 = 1 / _n2;
_inv_n = 2 / _n2;
_c = MathX.Square(cos_parallel1) + sin_parallel1 * _n2;
_c_over_n2 = _c * _inv_n2;
double a = _c - Math.Sin(latitude0_rad) * _n2;
if (a < 0)
{
throw new ArgumentOutOfRangeException();
}
_ro_0 = Math.Sqrt(a) * _inv_n;
}
protected internal override void Unproject(double x, double y, out double latitude, out double longitude)
{
double ro = Math.Sign(_n) * Math.Sqrt(x * x + MathX.Square(_ro_0 - y));
// If ro is zero or very small then then latitude will be +-Pi/2 depending on the sign of f.
latitude = 2 * Math.Atan(Math.Pow(_f / ro, _nInv)) - Math.PI / 2;
longitude = MathX.Clamp(Math.PI, Math.Atan2(x, _ro_0 - y) * _nInv);
}
