Navigation

Navigation refers to the ground coordinates assigned to the individual traces.

SEG-Y files may have navigation data associated with the traces in several ways: Group or source coordinates in the standard trace header locations, coordinates in non-standard trace header fields (e.g. byte offsets > 180 bytes), and/or external navigation files that map shot points to coordinates. For 2D SEG-Y files, the survey line may be projected onto a vertical cross-section plane if the trace coordinates are known.  Some SEG-Y files have no ground coordinate information available.

In this dialog, you may choose the source of the trace coordinates, or elect to display the traces sequentially with no coordinates or distances used – the data will not be projected.

Specify the how the X,Y locations of the individual traces are to be determined. By default, trace header bytes 81-84 (Group Coordinate X) are used for the trace X coordinate. You may select

  1. No coordinates - use along-line position. This option is used when the group coordinate location is unknown. The file can't be projected onto a section, but will be shown with equally-spaced traces, one trace per pixel or grid cell. The traces are assumed to be equally spaced along a straight line, ordered according to the specifications in Trace Order.

  2. Select trace header fields that contain the X and Y coordinates.

  3. Specify an external Navigation File  that maps a trace to coordinates.

Coordinate System

In order to properly georeference exported grids, databases, and Geosoft voxel files, you will need to associate a Coordinate System with the SEG-Y trace (navigation) coordinates.  By default, the Coordinate System is "unknown" and the horizontal units are "meters".  SEG-Y Reader will attempt to determine the correct horizontal units from several possible trace header fields and will display the units (feet or meters) here.  You may override these settings by clicking the [CoordSys] to bring up the Coordinate System Wizard.

The Coordinate System information is not used within SEG-Y Reader, but will be attached to any exported files.

See Also: