/// <summary>
/// Gets the standard zone.
/// </summary>
/// <param name="lat">latitude (degrees).</param>
/// <param name="lon">longitude (degrees).</param>
/// <param name="setzone">
/// zone override (optional). If omitted, use the standard rules for picking the zone.
/// If setzone is given then use that zone if it is non-negative, otherwise apply the rules given in <see cref="ZoneSpec"/>.
/// </param>
/// <returns></returns>
/// <remarks>
/// This is exact.
/// </remarks>
public static int StandardZone(double lat, double lon, int setzone = (int)ZoneSpec.Standard)
{
if (!(setzone >= (int)ZoneSpec.MinPseudoZone && setzone <= (int)ZoneSpec.MaxZone))
{
throw new GeographicException($"Illegal zone requested {setzone}");
}
if (setzone >= (int)ZoneSpec.MinZone || setzone == (int)ZoneSpec.Invalid)
{
return(setzone);
}
if (double.IsNaN(lat) || double.IsNaN(lon)) // Check if lat or lon is a NaN
{
return((int)ZoneSpec.Invalid);
}
if (setzone == (int)ZoneSpec.UTM || (lat >= -80 && lat < 84))
{
int ilon = (int)Floor(AngNormalize(lon));
if (ilon == 180)
{
ilon = -180; // ilon now in [-180,180)
}
int zone = (ilon + 186) / 6;
int band = MGRS.LatitudeBand(lat);
if (band == 7 && zone == 31 && ilon >= 3) // The Norway exception
{
zone = 32;
}
else if (band == 9 && ilon >= 0 && ilon < 42) // The Svalbard exception
{
zone = 2 * ((ilon + 183) / 12) + 1;
}
return(zone);
}
else
{
return((int)ZoneSpec.UPS);
}
}
