reSync

Description

reSync is a utility designed to re-synchronize sidescan data (specifically centre_no, no_samples, and offset fields) with corresponding depth detections within OMG-HDCS merged files. This tool is particularly useful when the sidescan information has become desynchronized or lost for certain beams, but is still present in adjacent pings.

It identifies sequences of pings where sidescan data is missing for beams that have depth detections, and then attempts to restore this information by copying it from the previous ping’s beams. This process can lead to some loss of specific sidescan data if there are no common beams with sidescan.

Usage 

reSync <mergefile(s)> [-v] [-testonly]

Arguments

Option Description
<mergefile(s)> Required. One or more paths to OMG-HDCS merged files to be processed. These files are modified in place unless -testonly is used.
-v Enable verbose output.
-testonly Runs the synchronization logic but does not write any changes back to the merged file. Useful for previewing potential synchronizations.

How It Works

  1. File Processing: The tool iterates through each provided merged file.
  2. Summary Header Reading: Reads the summary header for basic file information.
  3. Initial Beam State: Reads the raw beams from the first profile (ping 0) and stores them as before_beams.
  4. Profile Iteration: For each subsequent profile (ping k from 1 to summary.numProfiles - 1):
    • Detect Desynchronization: It checks if any beam in the current ping (beams[i]) has an observedDepth but no_samples == 0 (indicating missing sidescan data for a detected depth). If such a condition is found, it sets a dosync flag.
    • Synchronization (dosync and not -testonly): If dosync is active and not in testonly mode:
      • It iterates through all beams in the current ping.
      • For each beam i, if both beams[i].observedDepth (current ping’s depth detection) and before_beams[i].observedDepth (previous ping’s depth detection) are valid, it copies the centre_no, no_samples, and offset (sidescan data pointers) from before_beams[i] to after_beams[i].
      • If beams[i].observedDepth is valid but before_beams[i].observedDepth is not, the sidescan info for after_beams[i] is zeroed out, and a lost counter is incremented.
      • The after_beams (with restored sidescan info) are then written back to the current profile k in the merged file.
    • Update before_beams: Before processing the next ping, the beams from the current ping k are copied to before_beams to be used as a reference for ping k+1.
  5. In-Place Update: The merged file is modified in place, updating the sidescan data pointers for desynchronized beams.

Output Files

The input merged files are modified in-place (unless -testonly is used).

Dependencies

  • OMG_HDCS_jversion.h: For OMG-HDCS data structures.
  • support.h: For general utility functions and error handling.

Notes

Sidescan data can become desynchronized from bathymetry due to various reasons, including data acquisition issues or processing errors. This tool provides a heuristic approach to recover missing sidescan data pointers by assuming continuity from adjacent pings. This can be critical for generating complete sidescan mosaics. The tool modifies merged files in place, so backups are recommended. The -testonly option is useful for evaluating the effect of the synchronization before applying permanent changes.