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The Recalculate 3D Offsets module recomputes the signed offset value stored in each trace header for a 3D prestack dataset. For each trace it calculates the absolute source-to-receiver distance and then assigns a positive or negative sign depending on which side of the inline direction the receiver falls relative to the source. This signed offset convention is essential for correctly sorting 3D prestack gathers into near/far and positive/negative offset classes, and for any process that requires offset sign information such as AVO analysis, offset-dependent NMO, or Radon demultiple.
Use this module when trace offset headers have been lost, incorrectly imported, or when you need to enforce a consistent signed offset convention across a 3D survey. The inline azimuth can be read directly from the project bin grid or entered manually. Processing is multi-threaded for efficiency on large datasets.
The input seismic gather or dataset whose trace headers carry source and receiver coordinate fields (X and Y). These coordinates are used to compute the source-receiver distance and to determine the sign of each offset. The input data must have valid source and receiver coordinates assigned through the geometry application step before running this module.
The trace header collection associated with the input dataset. The module reads source (X, Y) and receiver (X, Y) coordinate fields from these headers to perform the offset recalculation. All other header fields are preserved unchanged in the output.
The 3D survey bin grid containing the inline azimuth of the survey. When the Use inline angle from bin grid parameter is enabled, the module reads the inline direction from this bin grid automatically. The bin grid must be defined and loaded into the project prior to running this module. If the inline azimuth is specified manually, this input is still required to be connected but its azimuth value will not be used.
Controls whether the module modifies the input trace vector in place or works on a copy. By default (disabled) the module creates a new copy of the trace collection and writes recalculated offsets into the copy, leaving the original data untouched. When enabled, offset values are written directly into the existing trace headers without making a copy, which reduces memory usage and speeds up processing. Use the unsafe mode only when the original offset values are no longer needed and you are certain no other step in the workflow depends on the unmodified input offsets.
When enabled (default), the inline azimuth is read directly from the project bin grid. This is the recommended setting for most workflows because it ensures the offset sign convention is consistent with the survey geometry as defined during binning. When disabled, the Inline azimuth field becomes available for manual entry. Disable this option only if the bin grid is not available or if you need to override the survey azimuth with a custom value.
Inline azimuth — visible only when Use inline angle from bin grid is disabled. Specifies the azimuth angle of the inline direction in degrees, measured clockwise from north. The sign of each recalculated offset is determined relative to this inline direction: receivers on one side of the line through the source parallel to the inline direction receive a positive offset, receivers on the other side receive a negative offset. Enter the correct survey inline azimuth to match the acquisition geometry.
When enabled, the calculated sign of each offset is flipped before being written to the trace header, effectively reversing the positive/negative offset convention. By default (disabled), the sign follows the natural convention determined by the inline azimuth. Use this option if downstream processing steps or displays show an inverted offset polarity compared to what is expected, or if the project sign convention differs from the default.