smthTimeOMG

Description

smthTimeOMG is a utility designed to smooth the timeOffset values stored in the profile headers of OMG-HDCS merged files. This is particularly useful for data derived from sources like SEGY, where time information might only be accurate to the integer second, but fractional second precision is needed for blending with other data (like heave).

The tool applies a moving average filter to the timeOffset values and can also apply a constant time shift.

Usage 

smthTimeOMG <OMG_HDCS_datafile(s)> [-v] [-test] [-filtlen <value>] [-Tshift <value>]

Arguments

Option Description  
<OMG_HDCS_datafile(s)> Required. One or more paths to OMG-HDCS merged files to be processed. These files are modified in place unless -test is used.  
-v Enable verbose output.  
-test Runs the smoothing operation but does not write any changes back to the merged file. Useful for previewing potential changes.  
-filtlen <value> Specifies the half-width of the moving average filter (number of pings on each side to average over). The total window size will be filtlen * 2. 3
-Tshift <value> Applies a constant time shift (in seconds) to the smoothed timeOffset values. 0

How It Works

  1. File Processing: The tool iterates through each specified merged file.
  2. Summary Header Reading & Time Scale Adjustment: Reads the summary header to get summary.numProfiles and summary.timeScale. The Tshift value is rescaled internally to match the units of timeOffset (microseconds * timeScale).
  3. Time Offset Extraction:
    • Allocates memory for two double arrays: timeOffset (to store original profile.timeOffset values) and low_timeOffset (for smoothed values).
    • Iterates through all profiles in the merged file, extracting and storing each profile.timeOffset into the timeOffset array.
  4. Moving Average Smoothing:
    • Copies the timeOffset array to low_timeOffset.
    • Iterates through profiles from filtlen to summary.numProfiles - filtlen - 1 (to ensure a full window is available).
    • For each profile i, it calculates the average of timeOffset values within the window [i - filtlen, i + filtlen - 1].
    • This average is then stored in low_timeOffset[i].
    • The Tshift (rescaled) is added to low_timeOffset[i].
  5. Writing Changes:
    • If -test is not used, the tool iterates through all profiles again.
    • For each profile i, it reads the original profile, updates its profile.timeOffset with the (integer cast of) low_timeOffset[i], and writes the modified profile back to the merged file.
  6. Cleanup: Closes files and frees dynamically allocated memory.

Output Files

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

Dependencies

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

Notes

Smoothing time offsets in merged files can significantly improve the accuracy of time-critical correlations with other data streams (e.g., heave, navigation). This is particularly important for raw data formats that may only provide coarse timestamping. The tool modifies merged files in-place, so backups are recommended. The -test option allows for previewing changes before committing.