2D SEG-Y Coordinate Mapping

Use the 2D SEG-Y Coordinate Mapping dialog to specify the CMP or Shotpoint field in the trace header and how that value will be mapped to real-world (X,Y) coordinates. If the (X,Y) coordinates are provided in the trace headers, specify which fields are to be used. If the (X,Y) coordinates are stored in an external navigation file, you may import that file and identify the appropriate fields within it.

In either case, you should also specify the coordinate system that the (X, Y) values represent, so that the survey is properly georeferenced.

For SEG-Y files that do not strictly conform to the standards, you have the option to select custom data types and non-standard trace-header locations; use the Trace Viewer to explore the trace headers and to determine the correct byte position and format for each of these fields.

2D SEG-Y Coordinate Mapping dialog options

Allow non-standard offsets

To properly interpret and georeference your seismic data, you might need to specify non-standard data type, size, and byte locations for key fields in the trace headers. Select "Yes" to enable selection of any odd byte position in the trace header. You may then specify the format of the 4-, 2-, or 1-byte value to be read, starting at that byte.

This selection is only necessary if both the position and data format of the trace header differ from the standard.

Select this option to view the trace-header values in standard locations; the file is scanned in this case using a standard set of formats and offsets.

Yes

Select this option if you need to select a non-standard position and data format for a trace header. Byte selection is now available from 1 to 239 – all the intermediate /odd offsets between the standard trace header locations are accessible.

If a non-standard position or format is specified for any of the trace headers, "N/A"will be displayed in the Minimum and Maximum fields. See the Application Notes below for further details.

CMP/Shotpoint coordinate

Specify the trace-header location of the CMP/Shotpoint coordinate. This is required to import 2D data.

Source of coordinates

Specify whether the X,Y coordinates are found in the trace headers, or they will be supplied by an external navigation file.

X,Y coordinates in trace headers

X coordinate

Specify the trace-header location of the X-coordinate of the trace location. In some cases, the X- & Y-coordinates may not be stored in the trace headers. In that case, the selections here will be ignored and overwritten.

Y coordinate

Specify the trace-header location of the Y-coordinate of the trace location. In some cases, the X- & Y-coordinates may not be stored in the trace headers. In that case, the selections here will be ignored and overwritten.

Coordinate scalar

This read-only field shows the coordinate scalar (scale factor) to be used for ground coordinates, which allows the integer values in the trace headers to be scaled by factors of 10. You may choose whether to apply this scalar to the selected X- and Y-coordinate fields.

X,Y coordinates in external file

Text file

Browse to find the file containing the navigation information for the seismic survey. This must be a delimited text file.

[Scan file]

Once you have identified the fields in this file, scan it to produce a list of available lines within the file.

Comment lines

Select the character that is used to identify comment lines in this file. Lines beginning with this character will be ignored.

X coordinate

Specify the field in the file containing the X coordinate.

Y coordinate

Specify the field in the file containing the Y coordinate.

CMP or Shot point

Specify the field in the file containing the CMP or Shot point. The equivalent value in the trace header will be used to match or interpolate coordinates in this file.

Line field

Specify the field in the file containing the Line names.

Selected line

Once the navigation file has been scanned, select from the list of lines in the file.

Coordinate system

Specify the coordinate system that the X- and Y-coordinate values represent. Output files will inherit this coordinate system.

To change the coordinate system information, use the Modify button located to the right of the field.

Coordinate system units

Read-only field that shows the horizontal units of the selected coordinate system.

If the vertical distance units differ from the horizontal units, they will be scaled to match the horizontal units before the output files are generated (grid, database, or voxel formats).

[More]

Click this button to display all of the non-zero trace headers that were detected in the file, including byte #, minimum value, maximum value, range, and step.

This can be useful when trying to determine the trace headers that store the coordinate fields specified in this dialog.

When using custom data types and/or non-standard trace-header locations, use the Trace Viewer to explore the trace headers and to determine the correct byte position and format.

[Text Header]

Click this button to view the Text Header in a separate, read-only window.

[Binary Header]

Click this button to view the Binary Header in a separate, read-only window.

[Trace Viewer]

Click this button to show the Trace Viewer in a separate, read-only window, which allows you to view the trace headers and trace data for any selected trace.

Application Notes

According to the SEG-Y standard(s), the Inline, Crossline, X-, and Y-coordinate fields are to be stored as 4-byte integers at predefined locations within the trace header. In non-compliant files, they may be stored at the correct location, but using formats such as 4-byte floating point values, or even 2-byte integers. You have the option to specify the format used to read the data at the selected position. In cases where both the position and data format of the trace header are non-standard, you may need to “Allow non-standard offsets” to allow selection of “in-between” (i.e., any odd byte index) positions.

The Trace Viewer has the same “Allow non-standard offsets” option. Use it to investigate the trace headers of any trace and find the correct fields; it interprets the bytes in each trace-header location in all supported formats.

Providing a new offset and format combination that is non-standard will set the Minimum and Maximum parameters to "N/A" (not available). To force recalculation of the minimum and maximum values, the trace headers will be rescanned, and the X ,Y coordinates will be recalculated based on your offset and format selection.