// longitude0, latitude0, parallel1, parallel2
public AlbersEqualAreaProjection(IDictionary <string, double> parameters)
: base(parameters)
{
var latitude0Rad = InputLatitude("latitude0");
var parallel1Rad = InputLatitude("parallel1");
var parallel2Rad = InputLatitude("parallel2");
var cosParallel1 = Math.Cos(parallel1Rad);
var sinParallel1 = Math.Sin(parallel1Rad);
_n2 = sinParallel1 + Math.Sin(parallel2Rad);
if (Math.Abs(_n2) <= MathX.Tolerance)
{
throw new ArgumentOutOfRangeException();
}
_n = _n2 / 2;
_nHalf = _n2 / 4;
var invN2 = 1 / _n2;
_invN = 2 / _n2;
_c = MathX.Square(cosParallel1) + sinParallel1 * _n2;
_cOverN2 = _c * invN2;
var a = _c - Math.Sin(latitude0Rad) * _n2;
if (a < 0)
{
throw new ArgumentOutOfRangeException();
}
_ro0 = Math.Sqrt(a) * _invN;
}
protected internal override void Unproject(double x, double y, out double latitude, out double longitude)
{
var ro = Math.Sign(_n) * Math.Sqrt(x * x + MathX.Square(_ro0 - y));
// If ro is zero or very small 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, _ro0 - y) * _nInv);
}
