/// <summary>
/// Decodes a coarse format TIS-B airborne position message.
/// </summary>
/// <param name="message"></param>
private void DecodeCoarseTisbAirbornePosition(AdsbMessage message)
{
message.MessageFormat = MessageFormat.CoarseTisbAirbornePosition;
var subMessage = message.CoarseTisbAirbornePosition = new CoarseTisbAirbornePosition();
message.TisbIcaoModeAFlag = _BitStream.ReadByte(1);
subMessage.SurveillanceStatus = (SurveillanceStatus)_BitStream.ReadByte(2);
subMessage.ServiceVolumeID = _BitStream.ReadByte(4);
var rawAltitude = _BitStream.ReadUInt16(12);
var acCode = ((rawAltitude & 0xfe0) >> 1) | (rawAltitude & 0x0f);
if ((rawAltitude & 0x10) != 0)
{
subMessage.BarometricAltitude = ModeSAltitudeConversion.CalculateBinaryAltitude(acCode);
}
else
{
subMessage.BarometricAltitude = ModeSAltitudeConversion.LookupGillhamAltitude(acCode);
}
var groundTrackValid = _BitStream.ReadBit();
var groundTrack = _BitStream.ReadByte(5);
var groundSpeed = _BitStream.ReadByte(6);
if (groundTrackValid)
{
subMessage.GroundTrack = (double)groundTrack * 11.25;
}
subMessage.GroundSpeed = (double)groundSpeed * 16.0;
subMessage.CompactPosition = ExtractCprCoordinate(message, 12, ignoreMessageType: true);
}
/// <summary>
/// Decodes an airborne position message.
/// </summary>
/// <param name="message"></param>
private void DecodeAirbornePosition(AdsbMessage message)
{
message.MessageFormat = message.Type == 0 ? MessageFormat.NoPositionInformation : MessageFormat.AirbornePosition;
var subMessage = message.AirbornePosition = new AirbornePositionMessage();
subMessage.SurveillanceStatus = (SurveillanceStatus)_BitStream.ReadByte(2);
if (IsFineFormatTisb(message))
{
message.TisbIcaoModeAFlag = _BitStream.ReadByte(1);
}
else
{
if (message.Type == 0)
{
_BitStream.Skip(1);
}
else
{
subMessage.NicB = (byte)(_BitStream.ReadBit() ? 2 : 0);
}
}
var rawAltitude = _BitStream.ReadUInt16(12);
var acCode = ((rawAltitude & 0xfe0) >> 1) | (rawAltitude & 0x0f);
int?altitude = null;
if ((rawAltitude & 0x10) != 0)
{
altitude = ModeSAltitudeConversion.CalculateBinaryAltitude(acCode);
}
else
{
altitude = ModeSAltitudeConversion.LookupGillhamAltitude(acCode);
}
if (message.Type < 20)
{
subMessage.BarometricAltitude = altitude;
}
else
{
subMessage.GeometricAltitude = altitude;
}
subMessage.PositionTimeIsExact = _BitStream.ReadBit();
subMessage.CompactPosition = ExtractCprCoordinate(message, 17);
}
private void ExtractAltitudeCode(ModeSMessage reply)
{
reply.Altitude = _BitStream.ReadUInt16(13);
reply.AltitudeIsMetric = (reply.Altitude & 0x40) != 0;
if (!reply.AltitudeIsMetric.Value)
{
int?decodedAltitude = ((reply.Altitude & 0x1F80) >> 2) | ((reply.Altitude & 0x20) >> 1) | (reply.Altitude & 0x0f);
if ((reply.Altitude & 0x10) != 0)
{
decodedAltitude = ModeSAltitudeConversion.CalculateBinaryAltitude(decodedAltitude.Value);
}
else
{
decodedAltitude = ModeSAltitudeConversion.LookupGillhamAltitude(decodedAltitude.Value);
}
reply.Altitude = decodedAltitude;
}
}
/// <summary>
/// Decodes an aircraft status message.
/// </summary>
/// <param name="message"></param>
private void DecodeAircraftStatus(AdsbMessage message)
{
message.MessageFormat = MessageFormat.AircraftStatus;
var subMessage = message.AircraftStatus = new AircraftStatusMessage();
subMessage.AircraftStatusType = (AircraftStatusType)_BitStream.ReadByte(3);
switch (subMessage.AircraftStatusType)
{
case AircraftStatusType.EmergencyStatus:
var emergency = subMessage.EmergencyStatus = new EmergencyStatus();
emergency.EmergencyState = (EmergencyState)_BitStream.ReadByte(3);
var modeA = (short)_BitStream.ReadUInt16(13);
if (modeA != 0)
{
emergency.Squawk = ModeS.ModeATranslator.DecodeModeA(modeA);
}
break;
case AircraftStatusType.TcasResolutionAdvisoryBroadcast:
var tcas = subMessage.TcasResolutionAdvisory = new TcasResolutionAdvisory();
var araCoding = _BitStream.ReadBit();
var araValue = (short)_BitStream.ReadUInt16(13);
tcas.ResolutionAdvisoryComplement = (ResolutionAdvisoryComplement)_BitStream.ReadByte(4);
tcas.ResolutionAdvisoryTerminated = _BitStream.ReadBit();
tcas.MultipleThreatEncounter = _BitStream.ReadBit();
if (araCoding)
{
tcas.SingleThreatResolutionAdvisory = (SingleThreatResolutionAdvisory)araValue;
}
else if (tcas.MultipleThreatEncounter)
{
tcas.MultipleThreatResolutionAdvisory = (MultipleThreatResolutionAdvisory)araValue;
}
switch (_BitStream.ReadByte(2))
{
case 1:
tcas.ThreatIcao24 = (int)_BitStream.ReadUInt32(24);
break;
case 2:
var threatAltitude = _BitStream.ReadUInt16(13);
var threatRange = _BitStream.ReadByte(7);
var threatBearing = _BitStream.ReadByte(6);
var strippedAltitude = ((threatAltitude & 0x1F80) >> 2) | ((threatAltitude & 0x20) >> 1) | (threatAltitude & 0x0f);
tcas.ThreatAltitude = ModeSAltitudeConversion.LookupGillhamAltitude(strippedAltitude);
if (threatRange > 0)
{
tcas.ThreatRange = ((float)(threatRange - 1) / 10F) + 0.05F;
tcas.ThreatRangeExceeded = threatRange == 127;
}
if (threatBearing > 0 && threatBearing < 61)
{
tcas.ThreatBearing = (short)((threatBearing - 1) * 6);
}
break;
}
break;
}
}
