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The Create Stack Line module automatically derives a 2D stack line (also called a crooked line or slalom line) from the source and receiver coordinates stored in the trace headers. This is essential for processing 2D land seismic surveys acquired along irregular or winding field routes, where a straight stacking line would cause significant CMP smearing and degraded stack quality.
The module works in several stages. First, it filters traces to retain only those with source-receiver offsets within the specified maximum offset, then derives a slalom line by fitting a smooth curve through the midpoint distribution. The resulting line is divided into regularly spaced bins of the chosen size, and the bin geometry (position, azimuth, and elevation) is computed for each point along the line. The output stack line can be used directly by subsequent binning and stacking steps.
Use this module at the geometry QC stage, before 2D binning, whenever the acquisition line deviates significantly from a straight path. The module requires that trace headers already contain valid source and receiver coordinates. If no sources or receivers are found in the headers, the module will report an error and will not produce a result.
The set of seismic trace headers from which source and receiver coordinates are read. These coordinates drive the entire stack line computation: the module uses midpoint positions (the average of each source-receiver pair) to determine the path of the line, and offset values to filter which traces contribute to the slalom fitting step. Ensure that X/Y coordinates and offsets are correctly populated in the headers before running this module.
The maximum source-receiver offset (in meters) of traces used to compute the shape of the slalom line. Only traces with an absolute offset smaller than this value are included when fitting the line path. Default: 2000 m. Restricting to near-offset traces produces a more accurate representation of the true CMP distribution along the line, because near-offset midpoints cluster tightly around the acquisition path. If your survey uses very short cables, reduce this value accordingly; if you need to include far-offset midpoints (for example, when near-offset coverage is sparse), increase it. Setting this value too large may cause the slalom line to wander away from the true acquisition path.
The spacing between consecutive bin centre points along the stack line, in meters. Default: 50 m. This value determines the CMP interval of the output 2D line and should match the nominal CMP spacing of your survey. Choosing a value that is too coarse will under-sample the line geometry and lead to poor bin shape definition on curved segments. Choosing a value that is too fine will produce a larger number of bins but will not add meaningful resolution beyond what the data density supports.
The spatial length of the smoothing window (in meters) applied to the raw midpoint distribution when fitting the slalom line path. Default: 500 m. A larger smoothing distance removes short-wavelength irregularities from the line path and produces a more gradual, geologically realistic stack line. A smaller value allows the line to follow tighter bends in the acquisition route. Set this value to a distance that preserves genuine bends while suppressing noise introduced by source/receiver positioning scatter. As a practical starting point, use a value of 3 to 5 times the station spacing.
The internal grid cell size (in meters) used when computing the midpoint density and line geometry during the slalom fitting process. Default: 50 m. This controls the resolution of the intermediate grid used to accumulate midpoints into spatial cells before the smoothing step. Smaller values give finer spatial detail but increase computation time. For most surveys this parameter can be left at its default, matching the Bin Step Out value. Only change it if you need to resolve very small-scale deviations in the acquisition path.
The spatial length of the smoothing window (in meters) applied to the elevation profile assigned to the stack line. Default: 0 m (no smoothing). After the stack line is computed, the module assigns an elevation (topography) value to each bin point derived from the source and receiver elevations. If the elevation values are noisy or exhibit high-frequency fluctuations due to GPS measurement errors, set this parameter to a positive distance value to apply a moving-average smooth over the elevation profile. Setting it to zero leaves the raw topography unchanged. The internal smoothing window length in number of bins is computed as this distance divided by the Bin Step Out value.
An optional path to a DAT text file where the computed stack line geometry will be saved. If a valid file path is provided, the module writes the bin point coordinates and picket numbers to this file, which can be inspected externally or reloaded by the Import Stack Line module. Leave this field empty if you do not need to export the stack line to a file.
The computed stack line, represented as an ordered sequence of bin centre points. Each point carries X/Y coordinates, an elevation value, a picket number, and an azimuth angle that describes the local direction of the line. This output is passed directly to the 2D binning module, which uses it to assign each trace to a bin along the crooked line. The map view of the stack line is also displayed in the interactive vista window after the module completes.
The total number of bin centre points in the computed stack line. This is a diagnostic output that you can check to confirm the line was successfully constructed and that the number of bins is consistent with the survey length divided by the Bin Step Out value.
The picket number (shotpoint-equivalent index) of the first bin point along the stack line. Together with the Last picket value, this defines the full picket range of the output line and can be used to verify that the line spans the expected portion of the survey.
The picket number of the last bin point along the stack line. Compare this with the First picket value to determine the total number of CMPs and to confirm the line reaches the end of the survey.