/// <summary>
/// Reads a single trace from the file.
/// </summary>
/// <param name="traceIndex">The trace index as it appears in squence in the file</param>
/// <returns>The segy trace</returns>
public SegyTrace ReadTrace(long traceIndex)
{
CodeContract.Requires(traceIndex < TraceCount, "Trace index to read must be less than the number of traces in the file.");
CodeContract.Requires(traceIndex >= 0, "Trace index must be greater than or equal to 0");
var islilEndian = IsLittleEndian;
_stream.Seek(0, SeekOrigin.Begin);
var textFileHeadersCount = FileTextualHeaders.Length;
var binaryHeader = FileBinaryHeader;
var dataStartIndex = TextHeaderBytesCount + BinaryHeaderBytesCount + TextHeaderBytesCount * (textFileHeadersCount - 1);
var sampleFormat = (FormatCode)binaryHeader.DataSampleFormatCode;
int sampleSz = SizeFrom(sampleFormat);
// as per rev 1, all data values are assumed big endian
var ns = binaryHeader.SamplesPerTraceOfFile;
var initStreamPosition = dataStartIndex + (240 + ns * sampleSz) * traceIndex;
CodeContract.Assume(initStreamPosition <= _stream.Length, "initial trace index exceeds file length.");
_stream.Seek(initStreamPosition, SeekOrigin.Begin);
var traceHeaderByteArr = _reader.ReadBytes(TraceHeaderBytesCount);
var trHeader = SegyTraceHeader.From(traceHeaderByteArr, islilEndian);
var traceDataBytesSz = trHeader.SampleCount * sampleSz;
var traceDataBytes = _reader.ReadBytes(traceDataBytesSz);
var traceData = GetData(traceDataBytes, sampleFormat, trHeader.SampleCount);
var seismicTrace = new SegyTrace {
ComponentAxis = 0, Data = traceData, Header = trHeader
};
return(seismicTrace);
}
/// <summary>
/// Appends a single segy trace to the end of the file or trace series.
/// </summary>
/// <param name="sgyTrace">The trace to write.</param>
public void Write(SegyTrace sgyTrace)
{
CodeContract.Requires(sgyTrace.Data.Length != 0);
if (TraceCount == 0)
{
TraceSampleCount = sgyTrace.Data.Length;
}
CodeContract.Assume(sgyTrace.Data.Length == TraceSampleCount);
_writer.BaseStream.Position = _writer.BaseStream.Length;
_writer.Write(sgyTrace.GetBytes());
TraceCount++;
}
