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;
}
}
public void BitStream_ReadUInt16_Throws_If_Reading_Less_Than_One_Or_More_Than_16_Bits()
{
for (int i = -2; i < 18; ++i)
{
_BitStream.Initialise(new byte[] { 0x00, 0x00 });
bool expectException = i < 1 || i > 16;
bool sawException = false;
try {
_BitStream.ReadUInt16(i);
} catch (ArgumentOutOfRangeException) {
sawException = true;
}
Assert.AreEqual(expectException, sawException, "ReadUInt16 did not behave correctly when asked to read {0} bits", i);
}
}
/// <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 (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>
/// 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);
}