private static (double longitude, double obliquity) swi_nutation(JulianDayNumber tjd, SweData swed)
{
// from interpolation, with three data points in 1-day steps;
// maximum error is about 3 mas
if (swed.InterpolateNutation)
{
// precalculated data points available
if (swed.InterpolatedNutation != null && tjd < swed.InterpolatedNutation.Time2 && tjd > swed.InterpolatedNutation.Time0)
{
var dx = (tjd - swed.InterpolatedNutation.Time0).Raw - 1.0;
var longitude = quadratic_intp(swed.InterpolatedNutation.DPsi0, swed.InterpolatedNutation.DPsi1, swed.InterpolatedNutation.DPsi2, dx);
var obliquity = quadratic_intp(swed.InterpolatedNutation.DEps0, swed.InterpolatedNutation.DEps1, swed.InterpolatedNutation.DEps2, dx);
return(longitude, obliquity);
}
else
{
var interpol = new InterpolatedNutation
{
Time0 = tjd.AddDays(-1.0), // one day earlier
Time2 = tjd.AddDays(1.0) // one day later
};
(interpol.DPsi0, interpol.DEps0) = calc_nutation(interpol.Time0, swed);
(interpol.DPsi2, interpol.DEps2) = calc_nutation(interpol.Time2, swed);
(interpol.DPsi1, interpol.DEps1) = calc_nutation(tjd, swed);
swed.InterpolatedNutation = interpol;
return(interpol.DPsi1, interpol.DEps1);
}
}
return(calc_nutation(tjd, swed));
}
internal static Nutation CalculateForSpeed(JulianDayNumber tjd, SweData swed) => Calculate(tjd.AddDays(-NUT_SPEED_INTV), swed);