Reader for SEGY files (SEG Y revision 1). The following data types are supported: unsigned or signed byte, short, int32, and float.

SEGY is a widely used format for storing seismic trace data, defined by the Society of Exploration Geophysicists publication "Digital Tape Standards" (http://www.seg.org). The VolumeViz reader supports all sizes of integer and float data, and can correctly determine the number of samples per trace in most cases.

The data will be mapped to the Open Inventor axes as follows:

• The trace length is mapped onto the Inventor X axis (time).

• The number of trace sensors per line is mapped onto the Inventor Y axis (inlines).

• Z is the number of lines (crosslines).

Although in most cases the SEGY reader can automatically detect if the number of traces per line in a SEGY file is not uniform, in some cases it cannot. However, be aware that the initialization for file reading will take longer when this environment variable is set. Missing data is assigned the value zero.

Although in most cases the SEGY reader can automatically detect if the length of traces in a SEGY data file is not uniform, in some cases it cannot. However, be aware that the initialization for file reading will take significantly longer when this environment variable is set. Missing data is assigned the value zero.

In most cases the SEGY reader can automatically detect if the values in the file need to be "byte swapped", for example if the data was written on a "big-endian" machine (e.g., SPARC) and is being read on a "little-endian" machine (e.g., Intel). If necessary you can force byte swapping on or off using the environment variable IVVR_SEGY_SWAPBYTES.

A value of 1 in the format field of the SEGY header normally means that the data values were written in IBM floating point format. But in some cases the values were actually written in IEEE floating point format (which should be indicated by format = 5). Normally the SEGY reader is able to detect this, but if necessary you can specify that float values are in IEEE format by setting environment variable IVVR_SEGY_FLOATISIEEE.

If the SEGY reader fails to read the file correctly, you can set the following environment variables:

• IVVR_SEGY_DEBUG=1 This outputs information of what the reader is actually doing.

• IVVR_SEGY_DUMP=filename This requests that some information of the file and trace headers be written to the specified file while processing the SEGY data file. All these information can be sent to the VSG support for assitance.

Limitations: In some circontances few first traces might be skipped, typically when the first line contains only one trace (this trace might be skipped). In such a case a message warns the application of how many traces are actually skipped (throught OIV.Inventor.Errors.SoDebugError).

See OIV.Inventor.SoPreferences for information on using environment variables.

In some cases information such as line numbers and crossline numbers will be stored in non-standard locations in the header. Applications can specify the byte position of values within the header using the OIV.VolumeViz.Readers.SoVRSegyFileReader.SetSegyTraceHeaderBytePosition(OIV.VolumeViz.Readers.SoVRSegyTraceHeaderBytePosition) method. Example :

SoVRSegyFileReader reader = new SoVRSegyFileReader();
SoVRSegyTraceHeaderBytePosition bytePos = new SoVRSegyTraceHeaderBytePosition();
bytePos.SetBytePosition(SoVRSegyTraceHeaderBytePosition.TraceAttributes.SEGY_INLINE   , 189);
bytePos.SetBytePosition(SoVRSegyTraceHeaderBytePosition.TraceAttributes.SEGY_CROSSLINE, 193);
reader.SetSegyTraceHeaderBytePosition(bytePos);
reader.SetFilename(theFilePath);

Information about the range of inline / crossline numbers and the range of time values can be queried using the OIV.VolumeViz.Readers.SoVRSegyFileReader.GetInlineRange(System.Int32@, System.Int32@, System.Int32@), OIV.VolumeViz.Readers.SoVRSegyFileReader.GetCrosslineRange(System.Int32@, System.Int32@, System.Int32@) and OIV.VolumeViz.Readers.SoVRSegyFileReader.GetZRange(System.Int32@, System.Int32@, System.Int32@) methods.

Applications can use this class to open a SEGY file and extract information from the file directly (in other words without necessarily creating a volume data node). To get the SEGY text file header call OIV.VolumeViz.Readers.SoVRSegyFileReader.GetSegyTextHeader(). To get the SEGY binary file header call OIV.VolumeViz.Readers.SoVRSegyFileReader.GetSegyFileHeader(OIV.VolumeViz.Readers.SoVRSegyFileHeader@, System.Boolean). To get the header of a specific trace call OIV.VolumeViz.Readers.SoVRSegyFileReader.GetSegyTraceHeader(System.Int32, OIV.VolumeViz.Readers.SoVRSegyTraceIdHeader@). To get the values in a specific trace call ().

Reference