private string DecodeAirbornePositionMsg(ModeSReply msg, DateTime timestamp)
{
// Airborne position message --> we need subsequent messages to decode
AirbornePositionMsg pos = (AirbornePositionMsg)msg;
if (msg.ICAO24 == null)
{
return("AirbornePositionMsg: No ICAO24 found.");
}
string icao24 = BitConverter.ToString(msg.ICAO24).Replace("-", String.Empty);
// check if ICAO is already stored in lookup table
ADSBInfo info = null;
if (!adsbinfos.TryGetValue(icao24, out info))
{
// no --> add new entry
info = new ADSBInfo();
info.ICAO24 = icao24;
adsbinfos.Add(icao24, info);
}
// adsbinfo found --> update information and calculate position
// contains valid position?
if (!pos.HasValidPosition)
{
// no --> return error meesage
return("[" + info.ICAO24 + "] AirbornePositionMsg: No valid position found.");
}
info.ICAO24 = icao24;
info.NICSupplementA = pos.NICSupplementA;
// position calculated before
if (!double.IsNaN(info.Lat) & !double.IsNaN(info.Lon))
{
try
{
// use local CPR
double[] localpos = pos.getLocalPosition(info.Lat, info.Lon);
// we have a pos --> store in info and update timestamp
info.Lat = localpos[0];
info.Lon = localpos[1];
if (pos.HasValidAltitude)
{
info.Alt = pos.Altitude;
}
info.Timestamp = timestamp;
return("[" + info.ICAO24 + "] AirbornePositionMsg: Lat= " + info.Lat.ToString("F8") + ", Lon=" + info.Lon.ToString("F8") + ", Alt= " + info.Alt.ToString() + ", Time= " + info.Timestamp.ToString("HH:mm:ss.fff"));
}
catch (Exception ex)
{
}
}
// no position calculated before
if (pos.IsOddFormat)
{
try
{
// odd message
info.LastOddAirborne = pos;
info.LastOddTimestamp = DateTime.UtcNow;
// check if even message was received before and not older than 10secs--> calculate global CPR
if ((info.LastEvenAirborne != null) && ((info.LastOddTimestamp - info.LastOddTimestamp).TotalSeconds <= 10))
{
try
{
double[] globalpos = pos.getGlobalPosition(info.LastEvenAirborne);
// we have a position --> store in info and update timestamp
info.Lat = globalpos[0];
info.Lon = globalpos[1];
if (pos.HasValidAltitude)
{
info.Alt = pos.Altitude;
}
// info.Timestamp = timestamp;
return("[" + info.ICAO24 + "] AirbornePositionMsg: Lat= " + info.Lat.ToString("F8") + ", Lon=" + info.Lon.ToString("F8") + ", Alt= " + info.Alt.ToString() + ", Time= " + info.Timestamp.ToString("HH:mm:ss.fff"));
}
catch
{
return("[" + info.ICAO24 + "] AirbornePositionMsg: Error while decoding position");
}
}
return("[" + info.ICAO24 + "] AirbornePositionMsg: No decoding possible yet");
}
catch (Exception ex)
{
}
}
// even message
info.LastEvenAirborne = pos;
info.LastEvenTimestamp = DateTime.UtcNow;
// check if odd message was received before and not older than 10secs --> calculate global CPR
if ((info.LastOddAirborne != null) && ((info.LastEvenTimestamp - info.LastOddTimestamp).TotalSeconds <= 10))
{
try
{
double[] globalpos = pos.getGlobalPosition(info.LastOddAirborne);
// we have a position --> store in info and update timestamp
info.Lat = globalpos[0];
info.Lon = globalpos[1];
if (pos.HasValidAltitude)
{
info.Alt = pos.Altitude;
}
// info.Timestamp = timestamp;
return("[" + info.ICAO24 + "] AirbornePositionMsg: Lat= " + info.Lat.ToString("F8") + ", Lon=" + info.Lon.ToString("F8") + ", Alt= " + info.Alt.ToString() + ", Time= " + info.Timestamp.ToString("HH:mm:ss.fff"));
}
catch
{
return("[" + info.ICAO24 + "] AirbornePositionMsg: Error while decoding position");
}
}
else
{
return("[" + info.ICAO24 + "] AirbornePositionMsg:No decoding possible yet");
}
}
/**
* This method can only be used if another position report with a different format (even/odd) is available
* and set with msg.setOtherFormatMsg(other).
* @param other airborne position message of the other format (even/odd). Note that the time between
* both messages should be not longer than 10 seconds!
* @return globally unambiguously decoded position tuple (latitude, longitude). The positional
* accuracy maintained by the Airborne CPR encoding will be approximately 5.1 meters.
* A message of the other format is needed for global decoding.
* @throws MissingInformationException if no position information is available in one of the messages
* @throws IllegalArgumentException if input message was emitted from a different transmitter
* @throws PositionStraddleError if position messages straddle latitude transition
* @throws BadFormatException other has the same format (even/odd)
*/
public double[] getGlobalPosition(AirbornePositionMsg other)
{
if (!other.ICAO24.SequenceEqual(ICAO24))
{
throw new IllegalArgumentException(
string.Format("Transmitter of other message (%s) not equal to this (%s):",
BitConverter.ToString(other.ICAO24).Replace("-", String.Empty), BitConverter.ToString(ICAO24).Replace("-", String.Empty)));
}
if (other.IsOddFormat == IsOddFormat)
{
throw new BadFormatException("Expected " + (IsOddFormat? "even":"odd") + " message format:" + other.ToString());
}
if (!horizontal_position_available)
{
throw new MissingInformationException("No position information available!");
}
if (!other.HasValidPosition)
{
throw new MissingInformationException("Other message has no position information.");
}
AirbornePositionMsg even = IsOddFormat?other:this;
AirbornePositionMsg odd = IsOddFormat?this:other;
// Helper for latitude single(Number of zones NZ is set to 15)
double Dlat0 = 360.0 / 60.0;
double Dlat1 = 360.0 / 59.0;
// latitude index
double j = Math.Floor((59.0 * even.CPREncodedLat - 60.0 * odd.CPREncodedLat) / ((double)(1 << 17)) + 0.5);
// global latitudes
double Rlat0 = Dlat0 * (mod(j, 60) + even.CPREncodedLat / ((double)(1 << 17)));
double Rlat1 = Dlat1 * (mod(j, 59) + odd.CPREncodedLat / ((double)(1 << 17)));
// Southern hemisphere?
if (Rlat0 >= 270 && Rlat0 <= 360)
{
Rlat0 -= 360;
}
if (Rlat1 >= 270 && Rlat1 <= 360)
{
Rlat1 -= 360;
}
// Northern hemisphere?
if (Rlat0 <= -270 && Rlat0 >= -360)
{
Rlat0 += 360;
}
if (Rlat1 <= -270 && Rlat1 >= -360)
{
Rlat1 += 360;
}
// ensure that the number of even longitude zones are equal
if (NL(Rlat0) != NL(Rlat1))
{
throw new PositionStraddleException(
"The two given position straddle a transition latitude " +
"and cannot be decoded. Wait for positions where they are equal.");
}
// Helper for longitude
double Dlon0 = 360.0 / Math.Max(1.0, NL(Rlat0));
double Dlon1 = 360.0 / Math.Max(1.0, NL(Rlat1) - 1);
// longitude index
double NL_helper = NL(IsOddFormat?Rlat1:Rlat0); // assuming that this is the newer message
double m = Math.Floor((even.CPREncodedLon * (NL_helper - 1) - odd.CPREncodedLon * NL_helper) / ((double)(1 << 17)) + 0.5);
// global longitude
double Rlon0 = Dlon0 * (mod(m, Math.Max(1.0, NL(Rlat0))) + even.CPREncodedLon / ((double)(1 << 17)));
double Rlon1 = Dlon1 * (mod(m, Math.Max(1.0, NL(Rlat1) - 1)) + odd.CPREncodedLon / ((double)(1 << 17)));
// correct longitude
if (Rlon0 < -180 && Rlon0 > -360)
{
Rlon0 += 360;
}
if (Rlon1 < -180 && Rlon1 > -360)
{
Rlon1 += 360;
}
if (Rlon0 > 180 && Rlon0 < 360)
{
Rlon0 -= 360;
}
if (Rlon1 > 180 && Rlon1 < 360)
{
Rlon1 -= 360;
}
return(new double[] { IsOddFormat?Rlat1 : Rlat0, IsOddFormat?Rlon1 : Rlon0 });
}
