/// <summary>
/// Returns Gps Outages times for a time interval or a prn, or a prn within a time interval.
/// </summary>
/// <param name="fromTime">The start time to look for outages.</param>
/// <param name="toTime">The end time to look for outages.</param>
/// <param name="prn">The prn whose outages are desired.</param>
/// <remarks>Note that either a from/to time or a prn (or both) must be supplied</remarks>
/// <returns>A string containing Gps outages.</returns>
public static async Task <string> GetGpsOutages(DateTime?fromTime = null,
DateTime?toTime = null,
int?prn = null)
{
if (fromTime == null && toTime == null && prn == null)
{
throw new ArgumentNullException("fromTime",
"You must specify either a from and to date or a prn number.");
}
var uri = Networking.GetFullUri(ServiceUris.NavigationGpsOutagesUri);
return(await Networking.HttpGetCall(Networking.AppendDateTimeAndPrnToUri(uri, fromTime, toTime, prn)));
}