/// <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);
}
/// <summary>
/// See interface docs.
/// </summary>
/// <param name="rawMessage"></param>
/// <param name="start"></param>
/// <param name="signalLevel"></param>
/// <param name="isMlat"></param>
/// <returns></returns>
public ModeSMessage Translate(byte[] rawMessage, int start, int?signalLevel, bool isMlat)
{
if (Statistics == null)
{
throw new InvalidOperationException("Statistics must be provided before Translate can do any work");
}
ModeSMessage result = null;
var messageLength = rawMessage == null ? 0 : rawMessage.Length - start;
if (messageLength > 6)
{
_BitStream.Initialise(rawMessage);
_BitStream.Skip(start * 8);
var downlinkFormatValue = _BitStream.ReadByte(5);
if (downlinkFormatValue >= 24)
{
downlinkFormatValue = 24;
_BitStream.Skip(-3);
}
bool isLongFrame = true;
switch (downlinkFormatValue)
{
case 16:
case 17:
case 18:
case 19:
case 20:
case 21:
case 24: if (messageLength > 13)
{
result = new ModeSMessage();
}
break;
default: isLongFrame = false; result = new ModeSMessage(); break;
}
if (result != null)
{
result.SignalLevel = signalLevel;
result.IsMlat = isMlat;
result.DownlinkFormat = (DownlinkFormat)downlinkFormatValue;
switch (result.DownlinkFormat)
{
case DownlinkFormat.ShortAirToAirSurveillance: DecodeShortAirToAirSurveillance(result); break; // DF0
case DownlinkFormat.SurveillanceAltitudeReply: DecodeSurveillanceAltitudeReply(result); break; // DF4
case DownlinkFormat.SurveillanceIdentityReply: DecodeSurveillanceIdentityReply(result); break; // DF5
case DownlinkFormat.AllCallReply: DecodeAllCallReply(result); break; // DF11
case DownlinkFormat.LongAirToAirSurveillance: DecodeLongAirToAirSurveillance(result); break; // DF16
case DownlinkFormat.ExtendedSquitter: DecodeExtendedSquitter(result); break; // DF17
case DownlinkFormat.ExtendedSquitterNonTransponder: DecodeExtendedSquitterNonTransponder(result); break; // DF18
case DownlinkFormat.MilitaryExtendedSquitter: DecodeMilitaryExtendedSquitter(result); break; // DF19
case DownlinkFormat.CommBAltitudeReply: DecodeCommBAltitudeReply(result); break; // DF20
case DownlinkFormat.CommBIdentityReply: DecodeCommBIdentityReply(result); break; // DF21
case DownlinkFormat.CommD: DecodeCommD(result); break; // DF24
}
if (Statistics != null)
{
Statistics.Lock(r => {
++r.ModeSMessagesReceived;
++r.ModeSDFStatistics[(int)result.DownlinkFormat].MessagesReceived;
if (isLongFrame)
{
++r.ModeSLongFrameMessagesReceived;
}
else
{
++r.ModeSShortFrameMessagesReceived;
}
});
}
}
}
return(result);
}
public void BitStream_Skip_Jumps_Over_Bits_In_The_Stream()
{
var binary = "11001010001101011101001111110000";
for (int i = 0; i < binary.Length; ++i)
{
var expectedBit = binary[i] == '1';
_BitStream.Initialise(ParseBinary(binary));
_BitStream.Skip(i);
Assert.AreEqual(expectedBit, _BitStream.ReadBit(), "Expected {0} after skipping {1} bits, ReadBit returned {2}", expectedBit, i, !expectedBit);
}
}
/// <summary>
/// See interface docs.
/// </summary>
/// <param name="rawMessage"></param>
/// <param name="start"></param>
/// <returns></returns>
public ModeSMessage Translate(byte[] rawMessage, int start)
{
ModeSMessage result = null;
var messageLength = rawMessage == null ? 0 : rawMessage.Length - start;
if (messageLength > 6)
{
_BitStream.Initialise(rawMessage);
_BitStream.Skip(start * 8);
var downlinkFormatValue = _BitStream.ReadByte(5);
if (downlinkFormatValue >= 24)
{
downlinkFormatValue = 24;
_BitStream.Skip(-3);
}
bool isLongFrame = true;
switch (downlinkFormatValue)
{
case 16:
case 17:
case 18:
case 19:
case 20:
case 21:
case 24: if (messageLength > 13)
{
result = new ModeSMessage();
}
break;
default: isLongFrame = false; result = new ModeSMessage(); break;
}
if (result != null)
{
result.DownlinkFormat = (DownlinkFormat)downlinkFormatValue;
switch (result.DownlinkFormat)
{
case DownlinkFormat.ShortAirToAirSurveillance: DecodeShortAirToAirSurveillance(result); break; // DF0
case DownlinkFormat.SurveillanceAltitudeReply: DecodeSurveillanceAltitudeReply(result); break; // DF4
case DownlinkFormat.SurveillanceIdentityReply: DecodeSurveillanceIdentityReply(result); break; // DF5
case DownlinkFormat.AllCallReply: DecodeAllCallReply(result); break; // DF11
case DownlinkFormat.LongAirToAirSurveillance: DecodeLongAirToAirSurveillance(result); break; // DF16
case DownlinkFormat.ExtendedSquitter: DecodeExtendedSquitter(result); break; // DF17
case DownlinkFormat.ExtendedSquitterNonTransponder: DecodeExtendedSquitterNonTransponder(result); break; // DF18
case DownlinkFormat.MilitaryExtendedSquitter: DecodeMilitaryExtendedSquitter(result); break; // DF19
case DownlinkFormat.CommBAltitudeReply: DecodeCommBAltitudeReply(result); break; // DF20
case DownlinkFormat.CommBIdentityReply: DecodeCommBIdentityReply(result); break; // DF21
case DownlinkFormat.CommD: DecodeCommD(result); break; // DF24
}
if (_Statistics.Lock != null)
{
lock (_Statistics.Lock) {
++_Statistics.ModeSMessagesReceived;
++_Statistics.ModeSDFCount[(int)result.DownlinkFormat];
if (isLongFrame)
{
++_Statistics.ModeSLongFrameMessagesReceived;
}
else
{
++_Statistics.ModeSShortFrameMessagesReceived;
}
}
}
}
}
return(result);
}